From 363106c4cefe7d08ca67cc77f3d38d4213190f31 Mon Sep 17 00:00:00 2001 From: David Hildenbrand Date: Thu, 24 Mar 2022 18:13:46 -0700 Subject: [PATCH] mm/khugepaged: remove reuse_swap_page() usage reuse_swap_page() currently indicates if we can write to an anon page without COW. A COW is required if the page is shared by multiple processes (either already mapped or via swap entries) or if there is concurrent writeback that cannot tolerate concurrent page modifications. However, in the context of khugepaged we're not actually going to write to a read-only mapped page, we'll copy the page content to our newly allocated THP and map that THP writable. All we have to make sure is that the read-only mapped page we're about to copy won't get reused by another process sharing the page, otherwise, page content would get modified. But that is already guaranteed via multiple mechanisms (e.g., holding a reference, holding the page lock, removing the rmap after copying the page). The swapcache handling was introduced in commit 10359213d05a ("mm: incorporate read-only pages into transparent huge pages") and it sounds like it merely wanted to mimic what do_swap_page() would do when trying to map a page obtained via the swapcache writable. As that logic is unnecessary, let's just remove it, removing the last user of reuse_swap_page(). Link: https://lkml.kernel.org/r/20220131162940.210846-7-david@redhat.com Signed-off-by: David Hildenbrand Reviewed-by: Yang Shi Acked-by: Vlastimil Babka Cc: Andrea Arcangeli Cc: Christoph Hellwig Cc: David Rientjes Cc: Don Dutile Cc: Hugh Dickins Cc: Jan Kara Cc: Jann Horn Cc: Jason Gunthorpe Cc: John Hubbard Cc: Kirill A. Shutemov Cc: Liang Zhang Cc: Matthew Wilcox (Oracle) Cc: Michal Hocko Cc: Mike Kravetz Cc: Mike Rapoport Cc: Nadav Amit Cc: Oleg Nesterov Cc: Peter Xu Cc: Rik van Riel Cc: Roman Gushchin Cc: Shakeel Butt Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- include/trace/events/huge_memory.h | 1 - mm/khugepaged.c | 11 ----------- 2 files changed, 12 deletions(-) diff --git a/include/trace/events/huge_memory.h b/include/trace/events/huge_memory.h index 4fdb14a..d651f34 100644 --- a/include/trace/events/huge_memory.h +++ b/include/trace/events/huge_memory.h @@ -29,7 +29,6 @@ EM( SCAN_VMA_NULL, "vma_null") \ EM( SCAN_VMA_CHECK, "vma_check_failed") \ EM( SCAN_ADDRESS_RANGE, "not_suitable_address_range") \ - EM( SCAN_SWAP_CACHE_PAGE, "page_swap_cache") \ EM( SCAN_DEL_PAGE_LRU, "could_not_delete_page_from_lru")\ EM( SCAN_ALLOC_HUGE_PAGE_FAIL, "alloc_huge_page_failed") \ EM( SCAN_CGROUP_CHARGE_FAIL, "ccgroup_charge_failed") \ diff --git a/mm/khugepaged.c b/mm/khugepaged.c index 1cdf7c3..a4e5eaf 100644 --- a/mm/khugepaged.c +++ b/mm/khugepaged.c @@ -46,7 +46,6 @@ enum scan_result { SCAN_VMA_NULL, SCAN_VMA_CHECK, SCAN_ADDRESS_RANGE, - SCAN_SWAP_CACHE_PAGE, SCAN_DEL_PAGE_LRU, SCAN_ALLOC_HUGE_PAGE_FAIL, SCAN_CGROUP_CHARGE_FAIL, @@ -683,16 +682,6 @@ static int __collapse_huge_page_isolate(struct vm_area_struct *vma, result = SCAN_PAGE_COUNT; goto out; } - if (!pte_write(pteval) && PageSwapCache(page) && - !reuse_swap_page(page)) { - /* - * Page is in the swap cache and cannot be re-used. - * It cannot be collapsed into a THP. - */ - unlock_page(page); - result = SCAN_SWAP_CACHE_PAGE; - goto out; - } /* * Isolate the page to avoid collapsing an hugepage -- 2.7.4