Gigantic bootmem HugeTLB pages are currently initialized from
hugetlb_init(), but page_alloc_init_late() runs earlier and walks
pageblocks to determine zone contiguity.
If a bootmem HugeTLB region is marked noinit, set_zone_contiguous() can
observe still-uninitialized struct pages through
__pageblock_pfn_to_page(). This may not trigger an immediate failure, but
it can make set_zone_contiguous() compute the wrong zone contiguity state.
If extra poisoned-page checks are added in this path, such as
PF_POISONED_CHECK() in page_zone_id(), it can also trigger an early boot
panic.
Initialize gigantic bootmem HugeTLB struct pages from
page_alloc_init_late(), before zone contiguity is evaluated, so later page
allocator setup only sees valid struct page state. This also makes the
initialization order more natural, as struct pages should be initialized
before later code inspects them.
Link: https://lore.kernel.org/20260612035903.2468601-5-songmuchun@bytedance.com
Fixes: fde1c4ecf9 ("mm: hugetlb: skip initialization of gigantic tail struct pages if freed by HVO")
Signed-off-by: Muchun Song <songmuchun@bytedance.com>
Acked-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
Acked-by: Oscar Salvador <osalvador@suse.de>
Cc: "Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com>
Cc: David Hildenbrand <david@kernel.org>
Cc: Frank van der Linden <fvdl@google.com>
Cc: Liam R. Howlett <liam@infradead.org>
Cc: Lorenzo Stoakes <ljs@kernel.org>
Cc: Madhavan Srinivasan <maddy@linux.ibm.com>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Nicholas Piggin <npiggin@gmail.com>
Cc: Oscar Salvador (SUSE) <osalvador@kernel.org>
Cc: "Ritesh Harjani (IBM)" <ritesh.list@gmail.com>
Cc: Usama Arif <usama.arif@linux.dev>
Cc: Vlastimil Babka <vbabka@kernel.org>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
vmemmap_populate_compound_pages() uses addr_pfn to determine the PFN
offset within a compound page and to decide whether the current vmemmap
slot should be populated as a head page mapping or should reuse a tail
page mapping.
However, addr_pfn is advanced manually in parallel with addr. The loop
itself progresses in vmemmap address space, so each PAGE_SIZE step in addr
covers PAGE_SIZE / sizeof(struct page) struct page slots. Since addr_pfn
is compared against nr_pages in data-PFN units, it should advance by the
same number of PFNs. The existing manual increments do not match that and
therefore do not reliably track the PFN corresponding to the current addr.
As a result, pfn_offset can be computed from the wrong PFN and the code
can make the head/tail decision for the wrong compound-page position.
Fix this by deriving addr_pfn directly from the current vmemmap address
instead of carrying it as loop state.
Link: https://lore.kernel.org/20260612035903.2468601-4-songmuchun@bytedance.com
Fixes: f2b79c0d79 ("powerpc/book3s64/radix: add support for vmemmap optimization for radix")
Signed-off-by: Muchun Song <songmuchun@bytedance.com>
Acked-by: Oscar Salvador <osalvador@suse.de>
Reviewed-by: Ritesh Harjani (IBM) <ritesh.list@gmail.com>
Cc: "Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com>
Cc: David Hildenbrand <david@kernel.org>
Cc: Frank van der Linden <fvdl@google.com>
Cc: Liam R. Howlett <liam@infradead.org>
Cc: Lorenzo Stoakes <ljs@kernel.org>
Cc: Madhavan Srinivasan <maddy@linux.ibm.com>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Mike Rapoport (Microsoft) <rppt@kernel.org>
Cc: Nicholas Piggin <npiggin@gmail.com>
Cc: Oscar Salvador (SUSE) <osalvador@kernel.org>
Cc: Usama Arif <usama.arif@linux.dev>
Cc: Vlastimil Babka <vbabka@kernel.org>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
__hugetlb_vmemmap_optimize_folios() uses incorrect arguments when handling
bootmem HugeTLB folios.
The section number passed to register_page_bootmem_memmap() is derived
from the vmemmap virtual address of folio->page instead of the folio PFN,
so the bootmem memmap metadata can be registered against the wrong
section. The helper is also given HUGETLB_VMEMMAP_RESERVE_SIZE even
though it expects a page count, not a size in bytes. In addition, the
write-protect range is based on pages_per_huge_page(h), which does not
cover the full HugeTLB vmemmap area and can leave part of the shared tail
vmemmap mapping writable.
Fix the section lookup to use folio_pfn(folio), use
HUGETLB_VMEMMAP_RESERVE_PAGES when registering the reserved memmap pages,
and use hugetlb_vmemmap_size(h) for the write-protect range.
Link: https://lore.kernel.org/20260612035903.2468601-3-songmuchun@bytedance.com
Fixes: 752fe17af6 ("mm/hugetlb: add pre-HVO framework")
Signed-off-by: Muchun Song <songmuchun@bytedance.com>
Acked-by: Oscar Salvador <osalvador@suse.de>
Reviewed-by: Frank van der Linden <fvdl@google.com>
Cc: "Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com>
Cc: David Hildenbrand <david@kernel.org>
Cc: Liam R. Howlett <liam@infradead.org>
Cc: Lorenzo Stoakes <ljs@kernel.org>
Cc: Madhavan Srinivasan <maddy@linux.ibm.com>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Mike Rapoport (Microsoft) <rppt@kernel.org>
Cc: Nicholas Piggin <npiggin@gmail.com>
Cc: Oscar Salvador (SUSE) <osalvador@kernel.org>
Cc: "Ritesh Harjani (IBM)" <ritesh.list@gmail.com>
Cc: Usama Arif <usama.arif@linux.dev>
Cc: Vlastimil Babka <vbabka@kernel.org>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Patch series "mm: Refactor bootmem gigantic hugepage allocation", v4.
This series is split out from the earlier larger series "mm: Generalize
HVO for HugeTLB and device DAX" [1]. It collects the first 19 patches of
that series as a standalone set of fixes and preparatory cleanups around
bootmem HugeTLB handling, sparse initialization ordering, and related
vmemmap setup.
The first patches fix a few bugs found while reviewing the existing code,
including incorrect bootmem HVO handling, wrong vmemmap registration
arguments, a powerpc compound-vmemmap tracking bug, and too-late
initialization of gigantic bootmem HugeTLB struct pages.
The rest of the series reorders early memory initialization so the
relevant zone state is available before sparse and HugeTLB boot-time setup
runs, then simplifies the remaining bootmem gigantic hugepage allocation
path and removes code made obsolete by that rework.
At a high level:
- patches [1-4] fix boot-time and arch-specific bugs
- patches [5-12] reorder and simplify sparse/mm/hugetlb early init
- patches [13-19] refactor bootmem gigantic hugepage allocation and
remove obsolete helpers and state
This patch (of 19):
Commit 622026e87c ("mm/hugetlb: remove fake head pages") switched
HVO to reuse per-zone shared tail pages from zone->vmemmap_tails[].
Those shared tail pages were initialized in hugetlb_vmemmap_init(), but
bootmem HugeTLB folios are prepared earlier from
gather_bootmem_prealloc(). With hugetlb_free_vmemmap=on,
prep_and_add_bootmem_folios() can access pageblock flags on bootmem
HugeTLB pages whose mirrored tail struct pages already point to the shared
tail page. On CONFIG_DEBUG_VM kernels, get_pfnblock_bitmap_bitidx() then
dereferences the still-uninitialized shared tail page and can panic during
boot.
Initialize zone->vmemmap_tails[] from gather_bootmem_prealloc(), before
bootmem HugeTLB folios are processed, and drop the later initialization
from hugetlb_vmemmap_init().
This bug only affects CONFIG_DEBUG_VM kernels, where the relevant
assertion is evaluated.
Link: https://lore.kernel.org/20260612035903.2468601-1-songmuchun@bytedance.com
Link: https://lore.kernel.org/20260612035903.2468601-2-songmuchun@bytedance.com
Fixes: 622026e87c ("mm/hugetlb: remove fake head pages")
Signed-off-by: Muchun Song <songmuchun@bytedance.com>
Acked-by: Oscar Salvador <osalvador@suse.de>
Tested-by: Michal Clapinski <mclapinski@google.com>
Reviewed-by: Michal Clapinski <mclapinski@google.com>
Cc: "Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com>
Cc: David Hildenbrand <david@kernel.org>
Cc: Liam R. Howlett <liam@infradead.org>
Cc: Lorenzo Stoakes <ljs@kernel.org>
Cc: Madhavan Srinivasan <maddy@linux.ibm.com>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Nicholas Piggin <npiggin@gmail.com>
Cc: "Ritesh Harjani (IBM)" <ritesh.list@gmail.com>
Cc: Vlastimil Babka <vbabka@kernel.org>
Cc: Frank van der Linden <fvdl@google.com>
Cc: Oscar Salvador (SUSE) <osalvador@kernel.org>
Cc: Usama Arif <usama.arif@linux.dev>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This code uses flag equivalences to try to optimise conversion from GFP_
to ALLOC_ but there's no clear reason to believe it makes things faster.
Even if it gets rid of conditional branches, it just trades them for a
data dependency.
CPUs are pretty good at conditional branches. But, in my GCC x86 build it
doesn't look like there are any branches anyway, the compiler found some
conditional instruction tricks. (Caveat: This was extracted & annotated
by Gemini AI, I did not actually read the disasm myself)
Old code:
ae50: 8b 04 24 mov (%rsp),%eax # Load gfp_mask
...
ae5d: 41 89 c4 mov %eax,%r12d
ae64: 41 81 e4 20 08 00 00 and $0x820,%r12d # Mask both flags at once
...
ae6f: 44 89 e1 mov %r12d,%ecx
ae77: 83 c9 40 or $0x40,%ecx # OR with ALLOC_CPUSET (0x40)
ae7a: 89 4c 24 60 mov %ecx,0x60(%rsp) # Store to alloc_flags
New code:
For __GFP_HIGH ( 0x20 ):
It uses the Carry Flag (via sbb ) to conditionally add 0x20 to the base 0x40 ( ALLOC_CPUSET ) flag:
ae63: 83 e0 20 and $0x20,%eax # Test __GFP_HIGH
...
ae6a: 83 f8 01 cmp $0x1,%eax # Set carry flag if 0
ae6f: 45 19 e4 sbb %r12d,%r12d # %r12d = (gfp & 0x20) ? 0 : -1
ae80: 41 83 e4 e0 and $0xffffffe0,%r12d # %r12d = (gfp & 0x20) ? 0 : -32
ae87: 41 83 c4 60 add $0x60,%r12d # %r12d = (gfp & 0x20) ? 0x60 : 0x40
For __GFP_KSWAPD_RECLAIM ( 0x800 ):
It uses a conditional move ( cmov ) later in the function to set the ALLOC_KSWAPD ( 0x800 ) bit:
ae72: 25 00 08 00 00 and $0x800,%eax # Test __GFP_KSWAPD_RECLAIM
ae77: 89 44 24 30 mov %eax,0x30(%rsp) # Store result
...
af2c: 80 cf 08 or $0x8,%bh # Set ALLOC_KSWAPD (0x800) in temp reg
af2f: 45 85 c9 test %r9d,%r9d # Check if __GFP_KSWAPD_RECLAIM was set
af32: 0f 44 d8 cmove %eax,%ebx # If not, revert to flags without it
Testing with a modified version[0] of lib/free_pages_test.c (adding
printks with timing)...
Old results from a Sapphire Rapids consumer CPU:
[ 67.157118] page_alloc_test: Testing with GFP_KERNEL
[ 67.157122] page_alloc_test: Starting 1,000,000 allocations...
[ 70.704446] page_alloc_test: Completed. Time: 3543002 us (Avg: 3543.00 ns per alloc+free loop)
[ 70.704456] page_alloc_test: Testing with GFP_KERNEL | __GFP_COMP
[ 70.704460] page_alloc_test: Starting 1,000,000 allocations...
[ 70.944672] page_alloc_test: Completed. Time: 239980 us (Avg: 239.98 ns per alloc+free loop)
[ 70.944675] page_alloc_test: Test completed
New results:
[ 70.079015] page_alloc_test: Testing with GFP_KERNEL
[ 70.079020] page_alloc_test: Starting 1,000,000 allocations...
[ 73.669396] page_alloc_test: Completed. Time: 3586954 us (Avg: 3586.95 ns per alloc+free loop)
[ 73.669402] page_alloc_test: Testing with GFP_KERNEL | __GFP_COMP
[ 73.669405] page_alloc_test: Starting 1,000,000 allocations...
[ 73.905084] page_alloc_test: Completed. Time: 235496 us (Avg: 235.49 ns per alloc+free loop)
[ 73.905086] page_alloc_test: Test completed
Seems like a wash.
So, drop the flag value coupling here and let the compiler and CPU do
their job. Superscalar CPUs are pretty neat after all.
(Used AI for the disasm but the rest is all manual).
Link: https://lore.kernel.org/20260629-gfp-pessimisation-v2-1-311ece6a8637@google.com
Link: https://lore.kernel.org/20260615-gfp-pessimisation-v2-1-65f1319e6818@google.com
Link: 2ccdc84ef0/page-alloc-test/page-alloc-test.c [1]
Signed-off-by: Brendan Jackman <jackmanb@google.com>
Reviewed-by: Zi Yan <ziy@nvidia.com>
Reviewed-by: Vlastimil Babka (SUSE) <vbabka@kernel.org>
Reviewed-by: Gregory Price <gourry@gourry.net>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Acked-by: Harry Yoo (Oracle) <harry@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Add a userspace filtering tool for page_owner that supports per-fd
filtering with print_mode and NUMA node filters.
Features:
- Three print modes: stack (default), handle, stack_handle
- NUMA node filtering with flexible formats (single: 0, multiple: 0,1,2,
range: 0-3, mixed: 0,2-3)
- Per-file-descriptor filter state for independent filtering
Usage examples:
# Filter by print mode
./page_owner_filter -m handle
./page_owner_filter -m stack_handle
# Filter by NUMA node
./page_owner_filter -n 0
./page_owner_filter -n 0-3
# Combined filters
./page_owner_filter -m stack -n 0,1,2
./page_owner_filter -m handle -n 0,2-3
The tool validates inputs before sending commands to the kernel and
provides clear error messages when the kernel does not support
per-fd filtering.
Link: https://lore.kernel.org/20260707115411.1714314-4-zhen.ni@easystack.cn
Signed-off-by: Zhen Ni <zhen.ni@easystack.cn>
Tested-by: Zi Yan <ziy@nvidia.com>
Acked-by: Vlastimil Babka (SUSE) <vbabka@kernel.org>
Acked-by: Zi Yan <ziy@nvidia.com>
Cc: Brendan Jackman <jackmanb@google.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Suren Baghdasaryan <surenb@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Add NUMA node filtering functionality to page_owner to allow filtering
pages by specific NUMA node(s). This is useful for NUMA-aware memory
allocation analysis and debugging.
The filter supports flexible input formats:
- Single node: nid=0
- Multiple nodes: nid=0,2,3
- Node range: nid=0-3
- Mixed format: nid=0,2-4,7
Example usage:
# Using the page_owner_filter tool (recommended)
./page_owner_filter -n 0-3
./page_owner_filter -m stack_handle -n 0,2-4,7
The implementation uses per-file-descriptor filter state stored in
file->private_data, allowing each opener to have independent filter
configuration. It uses nodemask_t for efficient multi-node filtering and
nodelist_parse() for flexible input parsing. Node validity is verified
using nodes_subset() to reject nodes without memory.
Link: https://lore.kernel.org/20260707115411.1714314-3-zhen.ni@easystack.cn
Signed-off-by: Zhen Ni <zhen.ni@easystack.cn>
Tested-by: Zi Yan <ziy@nvidia.com>
Acked-by: Zi Yan <ziy@nvidia.com>
Reviewed-by: Vlastimil Babka (SUSE) <vbabka@kernel.org>
Cc: Brendan Jackman <jackmanb@google.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Suren Baghdasaryan <surenb@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Patch series "mm/page_owner: add per-fd filter infrastructure for
print_mode and NUMA filtering", v12.
This patch series introduces per-file-descriptor filtering capabilities to the
page_owner feature.
Problem Statement
=================
In production environments with large memory configurations (e.g.,
250GB+), collecting page_owner information often results in files ranging
from several gigabytes to over 10GB. This creates significant challenges:
1. Storage pressure on production systems
2. Difficulty transferring large files from production environments
3. Post-processing overhead with tools/mm/page_owner_sort.c
The primary contributor to file size is redundant stack trace information.
While the kernel already deduplicates stacks via stackdepot, page_owner
retrieves and stores full stack traces for each page, only to deduplicate
them again during post-processing.
Additionally, in NUMA-aware environments (e.g., DPDK-based cloud
deployments where QEMU processes are bound to specific NUMA nodes), OOM
events are often node-specific rather than system-wide. Previously,
page_owner could not filter by NUMA node, forcing users to collect and
analyze data for all nodes.
Solution
========
This patch series introduces a per-file-descriptor filter infrastructure
with two initial filters:
1. **Print Mode Filter**: Outputs only stack handles instead of
full stack traces. The handle-to-stack mapping can be retrieved
from the existing show_stacks_handles interface. This dramatically
reduces output size while preserving all allocation metadata.
2. **NUMA Node Filter**: Allows filtering pages by specific NUMA node(s)
using flexible nodelist format, enabling targeted analysis of memory
issues in NUMA-aware deployments.
The per-fd design allows multiple concurrent page_owner reads with
different filters, solving coordination issues in multi-user production
environments.
Implementation
==============
The series is structured as follows:
- Patch 1: Implement print_mode filter infrastructure
* Add file->private_data to store per-fd filter state
* Add .open, .release, and .write file operations
* Support "stack", "handle", and "stack_handle" modes via "mode=" write commands
- Patch 2: Implement NUMA node filter infrastructure
* Add nid_filter field to per-fd state
* Support flexible nodelist format via "nid=" write commands (single, multiple, ranges)
* Validate nodes and reject non-existent nodes using nodes_subset()
- Patch 3: Add page_owner_filter userspace tool
* Manages per-fd filters via write() interface
* Provides user-friendly command-line interface
* Includes comprehensive input validation
- Patch 4: Document filter features and usage
Usage Example
=============
Using the page_owner_filter tool with per-fd filters:
# ./page_owner_filter -m stack_handle -n "0,2-3" -o page_owner.txt
The tool opens /sys/kernel/debug/page_owner, sets filters via write(),
then reads the filtered output to the specified file (or stdout).
Sample print_mode output (showing handles only):
Page allocated via order 0, mask 0x0(), pid 0, tgid 0 (swapper),
ts 0 ns PFN 0x40000 type Unmovable Block 512 type Unmovable
Flags 0x3fffe0000000000(node=0|zone=0|lastcpupid=0x1ffff)
handle: 1048577
Page allocated via order 0, mask 0x252000(__GFP_NOWARN|
__GFP_NORETRY|__GFP_COMP|__GFP_THISNODE), pid 0, tgid 0 (swapper),
ts 0 ns PFN 0x40002 type Unmovable Block 512 type Unmovable
Flags 0x23fffe0000000200(workingset|node=0|zone=0|lastcpupid=0x1ffff)
handle: 1048577
This patch (of 4):
Add a print_mode filter to page_owner that allows users to choose between
printing stack traces, stack handles, or both, providing flexibility for
different debugging and analysis scenarios.
The filter provides three modes via page_owner:
- Writing "mode=stack" prints stack traces for each page (default)
- Writing "mode=handle" prints only the handle number
- Writing "mode=stack_handle" prints both stack traces and handles
The default stack mode maintains backward compatibility with existing
usage, displaying complete stack traces for each page allocation.
The handle mode dramatically reduces log size and improves performance by
showing only the handle number instead of the full stack trace. Testing
shows handle mode reduces output size by ~66% (84MB vs 244MB) and improves
read performance by ~4.4x compared to full stack output. The mapping from
handles to actual stack traces can be obtained via the show_stacks_handles
interface.
The stack_handle mode prints both stack traces and handles, making it
easier to identify pages with the same allocation pattern by comparing
handle numbers instead of comparing large stack traces.
Example usage:
# Using the page_owner_filter tool (recommended)
./page_owner_filter -m stack # Print only stack traces (default)
./page_owner_filter -m handle # Print only handles
./page_owner_filter -m stack_handle # Print both stack and handles
Sample output (handle mode):
Page allocated via order 0, migratetype Unmovable, gfp_mask 0x1100ca,
pid 1, tgid 1 (systemd), ts 123456789 ns
PFN 0x1000 type Unmovable Block 1 type Unmovable
Flags 0x3fffe800000084(referenced|lru|active|private|node=0|zone=1)
handle: 17432583
...
This implementation uses per-file-descriptor filter state stored in
file->private_data, allowing each opener to have independent filter
configuration.
Link: https://lore.kernel.org/20260707115411.1714314-1-zhen.ni@easystack.cn
Link: https://lore.kernel.org/20260707115411.1714314-2-zhen.ni@easystack.cn
Signed-off-by: Zhen Ni <zhen.ni@easystack.cn>
Tested-by: Zi Yan <ziy@nvidia.com>
Acked-by: Zi Yan <ziy@nvidia.com>
Reviewed-by: Vlastimil Babka (SUSE) <vbabka@kernel.org>
Cc: Brendan Jackman <jackmanb@google.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Suren Baghdasaryan <surenb@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
print_page_owner_memcg() reads page->memcg_data via READ_ONCE() at the
start to guard against tail pages and NULL data. However, it later
re-reads page->memcg_data locklessly in two places:
1: page_memcg_check(page)
2: PageMemcgKmem(page) (via folio_memcg_kmem(), which includes
VM_BUG_ON assertions for tail pages and MEMCG_DATA_OBJEXTS)
If the page is concurrently freed and reallocated as a THP tail page or
slab page between these calls, the VM_BUG_ON assertions can trigger on
CONFIG_DEBUG_VM=y builds, crashing the kernel.
Fix both TOCTOU issues by using the memcg_data snapshot throughout.
Link: https://lore.kernel.org/20260714015117.78351-10-ye.liu@linux.dev
Fixes: fcf8935832 ("mm/page_owner: print memcg information")
Signed-off-by: Ye Liu <ye.liu@linux.dev>
Reported-by: Sashiko <sashiko-bot@kernel.org>
Reviewed-by: Zi Yan <ziy@nvidia.com>
Reviewed-by: Vlastimil Babka (SUSE) <vbabka@kernel.org>
Cc: Brendan Jackman <jackmanb@google.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Lorenzo Stoakes <ljs@kernel.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: David Hildenbrand (Arm) <david@kernel.org>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
The lockless buddy_order_unsafe() read can return a garbage order value if
the page is concurrently allocated between the PageBuddy check and the
private read. If this bogus order is <= MAX_PAGE_ORDER,
skip_buddy_pages() would arbitrarily advance the PFN, potentially jumping
past a MAX_ORDER_NR_PAGES boundary whose pfn_valid() check would have
caught an offline memory section.
In read_page_owner(), which relies solely on boundary-aligned pfn_valid()
to guard pfn_to_page(), skipping the boundary could cause pfn_to_page() to
access an unmapped mem_section.
Clamp the advance so it never crosses the next MAX_ORDER_NR_PAGES
boundary. This is safe for all three callers: the pageblock-iterating
ones already handle boundary transitions in their outer loops, and for
read_page_owner() the worst case is one extra PageBuddy check per 1024
pages when a bogus order would otherwise push past the boundary.
Link: https://lore.kernel.org/20260714015117.78351-9-ye.liu@linux.dev
Signed-off-by: Ye Liu <ye.liu@linux.dev>
Reviewed-by: Zi Yan <ziy@nvidia.com>
Reviewed-by: Vlastimil Babka (SUSE) <vbabka@kernel.org>
Cc: Brendan Jackman <jackmanb@google.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Lorenzo Stoakes <ljs@kernel.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: David Hildenbrand (Arm) <david@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
All of these symbols are file-scoped (static) in page_owner.c, so the
page_owner_ prefix is pure noise. Rename them to shorter, still-clear
names:
page_owner_stack_op -> stack_op
page_owner_stack_open -> stack_open
page_owner_stack_fops -> stack_fops
page_owner_pages_threshold -> pages_threshold
page_owner_threshold_get -> threshold_get
page_owner_threshold_set -> threshold_set
page_owner_threshold_fops -> threshold_fops
No functional change.
Link: https://lore.kernel.org/20260714015117.78351-8-ye.liu@linux.dev
Signed-off-by: Ye Liu <ye.liu@linux.dev>
Acked-by: Zi Yan <ziy@nvidia.com>
Reviewed-by: Vlastimil Babka (SUSE) <vbabka@kernel.org>
Cc: Brendan Jackman <jackmanb@google.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Lorenzo Stoakes <ljs@kernel.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: David Hildenbrand (Arm) <david@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
The free_ts_nsec field is a free-event timestamp, but it was printed in
the allocation summary line alongside ts_nsec (allocation time). Move it
to the free section where it logically belongs, together with free_pid and
free_tgid. This also makes __dump_page_owner() consistent with
print_page_owner(), which only prints ts_nsec in the allocation summary.
The output now groups all free-related information (pid, tgid, timestamp,
stack trace) in one place.
No functional change except output formatting.
Link: https://lore.kernel.org/20260714015117.78351-7-ye.liu@linux.dev
Signed-off-by: Ye Liu <ye.liu@linux.dev>
Acked-by: Zi Yan <ziy@nvidia.com>
Reviewed-by: Vlastimil Babka (SUSE) <vbabka@kernel.org>
Cc: Brendan Jackman <jackmanb@google.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Lorenzo Stoakes <ljs@kernel.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: David Hildenbrand (Arm) <david@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Replace all 'int reason' function parameters that carry migrate_reason
values with the proper 'enum migrate_reason' type. This makes the intent
explicit and leverages compiler type checking. The affected subsystems
are:
- page_owner: __folio_set_owner_migrate_reason(),
folio_set_owner_migrate_reason()
- migrate: migrate_pages(), migrate_pages_sync(),
migrate_pages_batch(), migrate_folios_move(),
migrate_hugetlbs(), unmap_and_move_huge_page()
- hugetlb: move_hugetlb_state(), htlb_allow_alloc_fallback()
- trace: mm_migrate_pages and mm_migrate_pages_start events
The 'short last_migrate_reason' struct field and internal helper parameter
in page_owner are intentionally left as 'short' since they store per-page
metadata where size matters.
No functional change.
Link: https://lore.kernel.org/20260714015117.78351-4-ye.liu@linux.dev
Signed-off-by: Ye Liu <ye.liu@linux.dev>
Reviewed-by: Zi Yan <ziy@nvidia.com>
Reviewed-by: Vlastimil Babka (SUSE) <vbabka@kernel.org>
Reviewed-by: Lorenzo Stoakes <ljs@kernel.org>
Acked-by: David Hildenbrand (Arm) <david@kernel.org>
Cc: Brendan Jackman <jackmanb@google.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Suren Baghdasaryan <surenb@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
The last_migrate_reason field uses -1 as a sentinel value to mean "no
migration has happened". Replace the four bare -1 occurrences by adding a
proper MR_NEVER member to enum migrate_reason, defining a corresponding
"never_migrated" string in the MIGRATE_REASON trace macro, and updating
the GDB page_owner script to use MR_NEVER instead of the hardcoded -1 so
that lx-dump-page-owner does not incorrectly report unmigrated pages as
migrated.
No functional change.
Link: https://lore.kernel.org/20260714015117.78351-3-ye.liu@linux.dev
Signed-off-by: Ye Liu <ye.liu@linux.dev>
Reviewed-by: Zi Yan <ziy@nvidia.com>
Reviewed-by: Vlastimil Babka (SUSE) <vbabka@kernel.org>
Cc: Brendan Jackman <jackmanb@google.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Lorenzo Stoakes <ljs@kernel.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: David Hildenbrand (Arm) <david@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Patch series "mm/page_owner: misc cleanups", v6.
This series collects a few cleanups for mm/page_owner.c that have been
accumulated while reading through the file. There is no functional change
-- the goal is to make the code easier to read and maintain.
Patch 1 consolidates three identical PageBuddy skip blocks into a single
skip_buddy_pages() helper, eliminating the duplication and keeping the
lockless-read comment in one place.
Patch 2 replaces the -1 magic number used for "never migrated" with a
proper MR_NEVER member in enum migrate_reason, adds the corresponding
"never_migrated" string in the MIGRATE_REASON trace macro, and updates the
GDB page_owner script to use MR_NEVER so that lx-dump-page-owner correctly
detects unmigrated pages.
Patch 3 follows up by converting the remaining 'int reason' parameters
throughout the migration and hugetlb callchains to 'enum migrate_reason',
making the type explicit and gaining compiler checking. The 'short
last_migrate_reason' struct field in page_owner is intentionally left as
'short' since it is per-page metadata where size matters.
Patch 4 hoists the CONFIG_MEMCG guard out of print_page_owner_memcg()'s
body so that the real implementation and the empty stub are two clearly
separate definitions, the common kernel idiom.
Patch 5 adds a missing \n to the count_threshold debugfs attribute format
string so that cat(1) output is properly terminated.
Patch 6 moves free_ts_nsec from the allocation summary line to the free
section in __dump_page_owner(), grouping it with free_pid and free_tgid
where it logically belongs. This also makes the dump output consistent
with print_page_owner().
Patch 7 drops the redundant page_owner_ prefix from file-scoped static
symbols (stack_fops, threshold_fops, etc.). Since they cannot collide
across translation units, the prefix carries no information.
Patch 8 clamps the PFN advance in skip_buddy_pages() at the next
MAX_ORDER_NR_PAGES boundary. The lockless buddy_order_unsafe() read can
return a garbage order value if the page is concurrently allocated between
the PageBuddy check and the private read, potentially causing the PFN to
advance past the next bounadry whose pfn_valid() check would have caught
an offline memory section. In read_page_owner(), which relies solely on
boundary-aligned pfn_valid() to guard pfn_to_page(), this could lead to an
unmapped mem_section access.
Patch 9 avoids two TOCTOU issues in print_page_owner_memcg() by reusing
the page->memcg_data snapshot already taken via READ_ONCE at the top of
the function throughout, instead of calling page_memcg_check() and
PageMemcgKmem() which re-read page->memcg_data locklessly with VM_BUG_ON
assertions. If the page is concurrently freed and reallocated as a THP
tail or slab page between the initial guards and these later calls, those
assertions can fire on CONFIG_DEBUG_VM=y builds. The OBJEXTS (slab) case
is also simplified with an early return since objcg != memcg for slabs.
This patch (of 6):
Three places in page_owner.c duplicate the same pattern: check if a page
is PageBuddy, read its order via buddy_order_unsafe(), advance the pfn
past the buddy block if the order is valid, and continue.
Consolidate them into a single inline helper skip_buddy_pages(). The
function returns true (skip) for any buddy page and advances @pfn past the
block when the order is valid; returns false if the page is not a buddy
page and should be processed normally.
The old init_pages_in_zone() variant used "order > 0" as an extra guard
before advancing pfn, but the continue was unconditional and (1UL << 0) -
1 == 0, so the behaviour is identical. The comment about zone->lock is
preserved in the helper's kernel-doc.
No functional change.
Link: https://lore.kernel.org/20260714015117.78351-1-ye.liu@linux.dev
Link: https://lore.kernel.org/20260714015117.78351-2-ye.liu@linux.dev
Signed-off-by: Ye Liu <ye.liu@linux.dev>
Reviewed-by: Zi Yan <ziy@nvidia.com>
Reviewed-by: Vlastimil Babka (SUSE) <vbabka@kernel.org>
Cc: Brendan Jackman <jackmanb@google.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Lorenzo Stoakes <ljs@kernel.org>
Cc: David Hildenbrand (Arm) <david@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Patch series "mm/kmemleak: avoid soft lockup when scanning task", v3.
kmemleak_scan() scans every task stack under one rcu_read_lock() with no
reschedule point, which can trip the soft lockup watchdog on hosts with
very many threads.
That prints the following message, depending on the workload+host
configuration:
watchdog: BUG: soft lockup - CPU#35 stuck for 22s! [kmemleak:537]
scan_block
kmemleak_scan
kmemleak_scan_thread
kthread
Patch 1 walks the tasks with find_ge_pid() so the scan reschedules between
tasks
Patches 2-3 let the scan loops stop early once a scan is interrupted.
This patch (of 3):
kmemleak_scan() walks every thread and scans its kernel stack under a
single rcu_read_lock() with no reschedule point. On a host with very many
threads -- amplified by KASAN/lockdep in debug builds -- this loop can hog
a CPU long enough to trip the soft lockup watchdog:
watchdog: BUG: soft lockup - CPU#35 stuck for 22s! [kmemleak:537]
scan_block
kmemleak_scan
kmemleak_scan_thread
kthread
A cond_resched() cannot be added directly: the loop runs inside an RCU
read-side critical section.
Walk the tasks one PID at a time with find_ge_pid(), taking the RCU read
lock only to look up and pin each task. The stack is then scanned with no
lock held, so cond_resched() runs between tasks and the scan stops early
on scan_should_stop(). This follows the next_tgid()/task_seq_get_next()
iteration pattern and keeps each RCU critical section short.
Link: https://lore.kernel.org/20260615-kmemleak-stack-resched-v3-0-acecd7d7fd92@debian.org
Link: https://lore.kernel.org/20260615-kmemleak-stack-resched-v3-1-acecd7d7fd92@debian.org
Fixes: c4b28963fd ("mm/kmemleak: rely on rcu for task stack scanning")
Signed-off-by: Breno Leitao <leitao@debian.org>
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Reviewed-by: Davidlohr Bueso <dave@stgolabs.net>
Reviewed-by: Lance Yang <lance.yang@linux.dev>
Reviewed-by: Oleg Nesterov <oleg@redhat.com>
Cc: Qian Cai <cai@lca.pw>
Cc: SeongJae Park <sj@kernel.org>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Commit 9a5b183941 ("mm, percpu: do not consider sleepable allocations
atomic") allows sleepable GFP_NOIO and GFP_NOFS percpu allocations to take
pcpu_alloc_mutex. This avoids premature allocation failures, but it also
makes the mutex visible to callers from constrained IO/FS contexts.
Thread A calls pcpu_alloc_noprof() with GFP_KERNEL and takes
pcpu_alloc_mutex. Since the internal allocation is not constrained by
NOFS, it may enter FS reclaim while still holding pcpu_alloc_mutex,
creating a dependency like: pcpu_alloc_mutex -> fs_reclaim -> FS lock
At the same time, Thread B may already hold an FS lock and then call
pcpu_alloc_noprof() with GFP_NOFS. It will try to acquire
pcpu_alloc_mutex and block, creating the reverse dependency: FS lock ->
pcpu_alloc_mutex
This can still form a potential deadlock cycle.
Avoid the dependency by restricting percpu backing allocations to
GFP_NOIO. The public allocation still uses the caller's GFP context to
decide whether it may block, but the internal memory allocations performed
while pcpu_alloc_mutex is held cannot recurse into IO or FS reclaim.
Link: https://lore.kernel.org/20260618130414.96383-5-kaitao.cheng@linux.dev
Fixes: 9a5b183941 ("mm, percpu: do not consider sleepable allocations atomic")
Signed-off-by: Kaitao Cheng <chengkaitao@kylinos.cn>
Cc: Christoph Lameter <cl@gentwo.org>
Cc: Dennis Zhou <dennis@kernel.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Pedro Falcato <pfalcato@suse.de>
Cc: Shivam Kalra <shivamkalra98@zohomail.in>
Cc: Tejun Heo <tj@kernel.org>
Cc: Uladzislau Rezki (Sony) <urezki@gmail.com>
Cc: Vlastimil Babka <vbabka@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
pcpu_depopulate_chunk() only needs the temporary pages array that was
already allocated by an earlier successful population attempt. Passing
GFP_KERNEL to pcpu_get_pages() in this path is misleading because the
depopulation path is not expected to allocate the array.
Teach pcpu_get_pages() to treat a zero gfp mask as a cached-only lookup
and add pcpu_get_pages_cached() for that use case. This keeps allocation
on the populate path tied to the caller supplied GFP mask while making the
depopulate path's dependency on the cached array explicit.
Link: https://lore.kernel.org/20260618130414.96383-4-kaitao.cheng@linux.dev
Signed-off-by: Kaitao Cheng <chengkaitao@kylinos.cn>
Suggested-by: Dennis Zhou <dennis@kernel.org>
Acked-by: Michal Hocko <mhocko@suse.com>
Cc: Christoph Lameter <cl@gentwo.org>
Cc: Pedro Falcato <pfalcato@suse.de>
Cc: Shivam Kalra <shivamkalra98@zohomail.in>
Cc: Tejun Heo <tj@kernel.org>
Cc: Uladzislau Rezki (Sony) <urezki@gmail.com>
Cc: Vlastimil Babka <vbabka@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
pcpu_alloc_noprof() derives pcpu_gfp from the caller supplied GFP mask and
passes it down to pcpu_populate_chunk(). pcpu_alloc_pages() already uses
that mask for backing page allocation.
However, the populate slow path still has internal allocations and page
table allocations which can lose the caller's allocation context. The
temporary pages array is allocated by pcpu_get_pages() with GFP_KERNEL,
and pcpu_map_pages() maps the backing pages through
vmap_pages_range_noflush() using GFP_KERNEL. The latter can allocate
vmalloc page tables implicitly, so a caller which deliberately uses
GFP_NOFS or GFP_NOIO can still enter FS or IO reclaim while populating a
percpu chunk.
This has the same concern as chunk creation: callers such as blk-cgroup
may use GFP_NOIO because they hold locks which can be involved in queue
freeze or IO reclaim dependencies. If an allocation reaches the percpu
slow path and needs to populate previously unbacked pages, the internal
GFP_KERNEL allocations can defeat that context.
One possible case is blk-cgroup after commit 5d726c4dbe ("blk-cgroup:
fix possible deadlock while configuring policy"). blkg_conf_prep() now
serializes against blkcg_deactivate_policy() with q->blkcg_mutex, and
blkg_alloc() was changed to GFP_NOIO for that reason:
CPU0: blkg_conf_prep()
mutex_lock(q->blkcg_mutex)
blkg_alloc(..., GFP_NOIO)
alloc_percpu_gfp(..., GFP_NOIO)
pcpu_alloc_noprof(..., GFP_NOIO)
pcpu_populate_chunk(GFP_NOIO)
pcpu_get_pages()
pcpu_map_pages()
-> if the selected percpu chunk has unpopulated pages,
chunk population may do internal GFP_KERNEL allocations
-> direct reclaim / writeback can issue IO to this queue
-> IO waits because the queue is frozen
CPU1: blkcg_deactivate_policy()
blk_mq_freeze_queue(q)
mutex_lock(q->blkcg_mutex)
-> waits for CPU0
... unfreeze only happens after q->blkcg_mutex is acquired/released
So the concern is that the caller deliberately uses GFP_NOIO because it
may hold a lock which can be acquired after queue freeze, but the percpu
slow path can temporarily lose that allocation context.
Pass pcpu_gfp through pcpu_get_pages(), pcpu_map_pages() and
__pcpu_map_pages(). Apply the corresponding memalloc scope around
vmap_pages_range_noflush(), because vmalloc page table allocation does not
pass the GFP mask down explicitly. Keep the first chunk setup path using
GFP_KERNEL, matching the previous early-init behavior.
Link: https://lore.kernel.org/20260618130414.96383-3-kaitao.cheng@linux.dev
Fixes: 9a5b183941 ("mm, percpu: do not consider sleepable allocations atomic")
Signed-off-by: Kaitao Cheng <chengkaitao@kylinos.cn>
Acked-by: Dennis Zhou <dennis@kernel.org>
Acked-by: Michal Hocko <mhocko@suse.com>
Cc: Christoph Lameter <cl@gentwo.org>
Cc: Pedro Falcato <pfalcato@suse.de>
Cc: Shivam Kalra <shivamkalra98@zohomail.in>
Cc: Tejun Heo <tj@kernel.org>
Cc: Uladzislau Rezki (Sony) <urezki@gmail.com>
Cc: Vlastimil Babka <vbabka@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Patch series "mm/percpu: Fix possible NOFS/NOIO reclaim recursion", v4.
Commit 9a5b183941 ("mm, percpu: do not consider sleepable allocations
atomic") allowed GFP_NOFS and GFP_NOIO percpu allocations to use
pcpu_alloc_mutex and the chunk creation slow path. This restored the
allocation capability that was lost when those constrained allocations
were treated as atomic, but it also makes the percpu slow path visible to
callers from constrained reclaim contexts.
There are two related problems.
First, the create and populate slow paths do not fully preserve the
caller's allocation constraints. pcpu_alloc_noprof() derives pcpu_gfp
from the caller supplied GFP mask and passes it down to the percpu backing
page allocator. However, chunk creation calls pcpu_get_vm_areas(), and
chunk population can allocate temporary metadata or vmalloc page tables
while mapping backing pages. Those internal allocations can still use
GFP_KERNEL, so a caller using GFP_NOFS or GFP_NOIO can enter unconstrained
FS or IO reclaim while holding pcpu_alloc_mutex.
One possible case is blk-cgroup after commit 5d726c4dbe ("blk-cgroup:
fix possible deadlock while configuring policy"). blkg_conf_prep() now
serializes against blkcg_deactivate_policy() with q->blkcg_mutex, and
blkg_alloc() uses GFP_NOIO because queue freeze and IO reclaim
dependencies can otherwise deadlock. If the percpu slow path loses that
GFP_NOIO context, direct reclaim or writeback can issue IO to a frozen
queue while q->blkcg_mutex is held.
Second, allowing sleepable GFP_NOFS/GFP_NOIO allocations to take
pcpu_alloc_mutex means that unconstrained backing allocations made under
the mutex can create an FS/IO reclaim dependency against a constrained
caller which already holds an FS or IO lock and then waits for
pcpu_alloc_mutex.
This series fixes those issues in three steps:
- pass the caller supplied GFP mask into pcpu_get_vm_areas() and use it
for vmalloc metadata and KASAN shadow allocations;
- pass the GFP mask through the chunk population path, including the
temporary pages array and vmalloc page table allocation scope;
- restrict percpu backing allocations performed while holding
pcpu_alloc_mutex to GFP_NOIO, so they cannot recurse into IO or FS
reclaim.
This keeps sleepable GFP_NOFS/GFP_NOIO percpu allocations working, while
avoiding the reclaim recursion risks introduced by making those
allocations eligible for the mutex-protected slow path.
This patch (of 4):
pcpu_alloc_noprof() derives pcpu_gfp from the caller supplied GFP mask and
passes it down to the backing percpu allocator. However, when the percpu
vmalloc allocator has to create a new chunk, pcpu_create_chunk() calls
pcpu_get_vm_areas() to allocate the corresponding vmalloc areas.
pcpu_get_vm_areas() currently performs its internal allocations with
GFP_KERNEL, including vmap area metadata, vm_struct metadata and KASAN
vmalloc shadow population. This means that a caller which deliberately
uses GFP_NOFS or GFP_NOIO can still enter FS or IO reclaim while creating
the vmalloc areas for a new percpu chunk.
One possible case is blk-cgroup after commit 5d726c4dbe ("blk-cgroup:
fix possible deadlock while configuring policy"). blkg_conf_prep() now
serializes against blkcg_deactivate_policy() with q->blkcg_mutex, and
blkg_alloc() was changed to GFP_NOIO for that reason:
CPU0: blkg_conf_prep()
mutex_lock(q->blkcg_mutex)
blkg_alloc(..., GFP_NOIO)
alloc_percpu_gfp(..., GFP_NOIO)
pcpu_alloc_noprof(..., GFP_NOIO)
pcpu_create_chunk(GFP_NOIO)
pcpu_get_vm_areas()
-> if percpu chunks are exhausted, chunk create may do
internal GFP_KERNEL allocations
-> direct reclaim / writeback can issue IO to this queue
-> IO waits because the queue is frozen
CPU1: blkcg_deactivate_policy()
blk_mq_freeze_queue(q)
mutex_lock(q->blkcg_mutex)
-> waits for CPU0
... unfreeze only happens after q->blkcg_mutex is acquired/released
So the concern is that the caller deliberately uses GFP_NOIO because it
may hold a lock which can be acquired after queue freeze, but the percpu
slow path can temporarily lose that allocation context.
Pass the caller supplied GFP mask from pcpu_create_chunk() to
pcpu_get_vm_areas(), and use it for the internal vmalloc metadata and
KASAN shadow allocations.
Link: https://lore.kernel.org/20260618130414.96383-1-kaitao.cheng@linux.dev
Link: https://lore.kernel.org/20260618130414.96383-2-kaitao.cheng@linux.dev
Fixes: 9a5b183941 ("mm, percpu: do not consider sleepable allocations atomic")
Signed-off-by: Kaitao Cheng <chengkaitao@kylinos.cn>
Reviewed-by: Uladzislau Rezki (Sony) <urezki@gmail.com>
Reviewed-by: Shivam Kalra <shivamkalra98@zohomail.in>
Acked-by: Dennis Zhou <dennis@kernel.org>
Acked-by: Michal Hocko <mhocko@suse.com>
Cc: Christoph Lameter <cl@gentwo.org>
Cc: Pedro Falcato <pfalcato@suse.de>
Cc: Tejun Heo <tj@kernel.org>
Cc: Vlastimil Babka <vbabka@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Patch series "mm/filemap: reduce unnecessary xarray lookups".
This series optimizes xarray lookups in filemap by avoiding redundant
iterations after obtaining the last needed folio. The boundary check is
moved to before advancing the xarray iterator, eliminating unnecessary
lookups and branches in the fast path. This reduces the overhead of
filemap_get_read_batch() from 2.91% to 2.53% in 4k read tests.
This patch (of 2):
When reading small amounts of data from the page cache, only a single
folio is typically returned from filemap_read_get_batch(). In this case,
calling xas_advance() or xas_next() after adding the folio to the batch is
unnecessary and only introduces extra branches.
The same issue exists for large reads, where one additional xarray walk is
always performed before termination.
Quit the loop once we get the last folio in the range, so the final
redundant xarray advancement can be avoided.
The xas_next() does not update xa_index when xas->xa_node is set to
XAS_RESTART, so the put and retry path would not update xa_index, hence
the warning should therefore never trigger.
During the 4k reads test, the overhead of this function dropped from 2.91%
to 2.53%.
Link: https://lore.kernel.org/20260620062446.351475-2-chizhiling@163.com
Signed-off-by: Chi Zhiling <chizhiling@kylinos.cn>
Suggested-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Reviewed-by: Jan Kara <jack@suse.cz>
Cc: Chi Zhiling <chizhiling@kylinos.cn>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
