From: Kiryl Shutsemau Date: Tue, 23 Sep 2025 11:07:09 +0000 (+0100) Subject: mm/fault: try to map the entire file folio in finish_fault() X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=19773df031bcc67d5caa06bf0ddbbff40174be7a;p=thirdparty%2Fkernel%2Fstable.git mm/fault: try to map the entire file folio in finish_fault() finish_fault() uses per-page fault for file folios. This only occurs for file folios smaller than PMD_SIZE. The comment suggests that this approach prevents RSS inflation. However, it only prevents RSS accounting. The folio is still mapped to the process, and the fact that it is mapped by a single PTE does not affect memory pressure. Additionally, the kernel's ability to map large folios as PMD if they are large enough does not support this argument. When possible, map large folios in one shot. This reduces the number of minor page faults and allows for TLB coalescing. Mapping large folios at once will allow the rmap code to mlock it on add, as it will recognize that it is fully mapped and mlocking is safe. Link: https://lkml.kernel.org/r/20250923110711.690639-5-kirill@shutemov.name Signed-off-by: Kiryl Shutsemau Reviewed-by: Shakeel Butt Reviewed-by: Baolin Wang Cc: David Hildenbrand Cc: Johannes Weiner Cc: Lorenzo Stoakes Signed-off-by: Andrew Morton --- diff --git a/mm/memory.c b/mm/memory.c index 17cebb97beaea..74b45e258323e 100644 --- a/mm/memory.c +++ b/mm/memory.c @@ -5516,13 +5516,8 @@ fallback: nr_pages = folio_nr_pages(folio); - /* - * Using per-page fault to maintain the uffd semantics, and same - * approach also applies to non shmem/tmpfs faults to avoid - * inflating the RSS of the process. - */ - if (!vma_is_shmem(vma) || unlikely(userfaultfd_armed(vma)) || - unlikely(needs_fallback)) { + /* Using per-page fault to maintain the uffd semantics */ + if (unlikely(userfaultfd_armed(vma)) || unlikely(needs_fallback)) { nr_pages = 1; } else if (nr_pages > 1) { pgoff_t idx = folio_page_idx(folio, page);