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khugepaged: optimize __collapse_huge_page_copy_succeeded() by PTE batching

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Use PTE batching to batch process PTEs mapping the same large folio. An
improvement is expected due to batching refcount-mapcount manipulation on
the folios, and for arm64 which supports contig mappings, the number of
TLB flushes is also reduced.

Link: https://lkml.kernel.org/r/20250724052301.23844-3-dev.jain@arm.com
Signed-off-by: Dev Jain <dev.jain@arm.com>
Acked-by: David Hildenbrand <david@redhat.com>
Reviewed-by: Baolin Wang <baolin.wang@linux.alibaba.com>
Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Cc: Barry Song <baohua@kernel.org>
Cc: Liam Howlett <liam.howlett@oracle.com>
Cc: Mariano Pache <npache@redhat.com>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: Zi Yan <ziy@nvidia.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Dev Jain
2025-07-24 10:53:00 +05:30
committed by Andrew Morton
parent 3dfde97800
commit 4ea3594a47
1 changed files with 18 additions and 7 deletions
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25
mm/khugepaged.c
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@@ -700,12 +700,15 @@ static void __collapse_huge_page_copy_succeeded(pte_t *pte,
spinlock_t *ptl,
struct list_head *compound_pagelist)
{
unsigned long end = address + HPAGE_PMD_SIZE;
struct folio *src, *tmp;
pte_t *_pte;
pte_t pteval;
pte_t *_pte;
unsigned int nr_ptes;
for (_pte = pte; _pte < pte + HPAGE_PMD_NR;
_pte++, address += PAGE_SIZE) {
for (_pte = pte; _pte < pte + HPAGE_PMD_NR; _pte += nr_ptes,
address += nr_ptes * PAGE_SIZE) {
nr_ptes = 1;
pteval = ptep_get(_pte);
if (pte_none(pteval) || is_zero_pfn(pte_pfn(pteval))) {
add_mm_counter(vma->vm_mm, MM_ANONPAGES, 1);
@@ -722,18 +725,26 @@ static void __collapse_huge_page_copy_succeeded(pte_t *pte,
struct page *src_page = pte_page(pteval);
src = page_folio(src_page);
if (!folio_test_large(src))
if (folio_test_large(src)) {
unsigned int max_nr_ptes = (end - address) >> PAGE_SHIFT;
nr_ptes = folio_pte_batch(src, _pte, pteval, max_nr_ptes);
} else {
release_pte_folio(src);
}
/*
* ptl mostly unnecessary, but preempt has to
* be disabled to update the per-cpu stats
* inside folio_remove_rmap_pte().
*/
spin_lock(ptl);
ptep_clear(vma->vm_mm, address, _pte);
folio_remove_rmap_pte(src, src_page, vma);
clear_ptes(vma->vm_mm, address, _pte, nr_ptes);
folio_remove_rmap_ptes(src, src_page, nr_ptes, vma);
spin_unlock(ptl);
free_folio_and_swap_cache(src);
free_swap_cache(src);
folio_put_refs(src, nr_ptes);
}
}