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After commitacd7ccb284("mm: shmem: add large folio support for tmpfs"), tmpfs can also support large folio allocation (not just PMD-sized large folios). However, when accessing tmpfs via mmap(), although tmpfs supports large folios, we still establish mappings at the base page granularity, which is unreasonable. We can map multiple consecutive pages of tmpfs folios at once according to the size of the large folio. On one hand, this can reduce the overhead of page faults; on the other hand, it can leverage hardware architecture optimizations to reduce TLB misses, such as contiguous PTEs on the ARM architecture. Moreover, tmpfs mount will use the 'huge=' option to control large folio allocation explicitly. So it can be understood that the process's RSS statistics might increase, and I think this will not cause any obvious effects for users. Performance test: I created a 1G tmpfs file, populated with 64K large folios, and write-accessed it sequentially via mmap(). I observed a significant performance improvement: Before the patch: real 0m0.158s user 0m0.008s sys 0m0.150s After the patch: real 0m0.021s user 0m0.004s sys 0m0.017s Link: https://lkml.kernel.org/r/440940e78aeb7430c5cc8b6d2088ae98265b9809.1751599072.git.baolin.wang@linux.alibaba.com Fixes:acd7ccb284("mm: shmem: add large folio support for tmpfs") Signed-off-by: Baolin Wang <baolin.wang@linux.alibaba.com> Acked-by: David Hildenbrand <david@redhat.com> Acked-by: Zi Yan <ziy@nvidia.com> Reviewed-by: Vishal Moola (Oracle) <vishal.moola@gmail.com> Reviewed-by: Barry Song <baohua@kernel.org> Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com> Cc: Baolin Wang <baolin.wang@linux.alibaba.com> Cc: Dev Jain <dev.jain@arm.com> Cc: Hugh Dickins <hughd@google.com> Cc: Liam Howlett <liam.howlett@oracle.com> Cc: Mariano Pache <npache@redhat.com> Cc: Michal Hocko <mhocko@suse.com> Cc: Mike Rapoport <rppt@kernel.org> Cc: Ryan Roberts <ryan.roberts@arm.com> Cc: Suren Baghdasaryan <surenb@google.com> Cc: Vlastimil Babka <vbabka@suse.cz> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the reStructuredText markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.