+ mm-khugepaged-remove-reuse_swap_page-usage.patch added to -mm tree

+ mm-khugepaged-remove-reuse_swap_page-usage.patch added to -mm tree

[akpm]

The patch titled
     Subject: mm/khugepaged: remove reuse_swap_page() usage
has been added to the -mm tree.  Its filename is
     mm-khugepaged-remove-reuse_swap_page-usage.patch

This patch should soon appear at
    https://ozlabs.org/~akpm/mmots/broken-out/mm-khugepaged-remove-reuse_swap_page-usage.patch
and later at
    https://ozlabs.org/~akpm/mmotm/broken-out/mm-khugepaged-remove-reuse_swap_page-usage.patch

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------------------------------------------------------
From: David Hildenbrand <david@redhat.com>
Subject: 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 <david@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: David Rientjes <rientjes@google.com>
Cc: Don Dutile <ddutile@redhat.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Jan Kara <jack@suse.cz>
Cc: Jann Horn <jannh@google.com>
Cc: Jason Gunthorpe <jgg@nvidia.com>
Cc: John Hubbard <jhubbard@nvidia.com>
Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Liang Zhang <zhangliang5@huawei.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Mike Rapoport <rppt@linux.ibm.com>
Cc: Nadav Amit <nadav.amit@gmail.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Peter Xu <peterx@redhat.com>
Cc: Rik van Riel <riel@surriel.com>
Cc: Roman Gushchin <guro@fb.com>
Cc: Shakeel Butt <shakeelb@google.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Yang Shi <shy828301@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 include/trace/events/huge_memory.h |    1 -
 mm/khugepaged.c                    |   11 -----------
 2 files changed, 12 deletions(-)

--- a/include/trace/events/huge_memory.h~mm-khugepaged-remove-reuse_swap_page-usage
+++ a/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")	\
--- a/mm/khugepaged.c~mm-khugepaged-remove-reuse_swap_page-usage
+++ a/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(
 			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
_

Patches currently in -mm which might be from david@redhat.com are

mm-optimize-do_wp_page-for-exclusive-pages-in-the-swapcache.patch
mm-optimize-do_wp_page-for-fresh-pages-in-local-lru-pagevecs.patch
mm-slightly-clarify-ksm-logic-in-do_swap_page.patch
mm-streamline-cow-logic-in-do_swap_page.patch
mm-huge_memory-streamline-cow-logic-in-do_huge_pmd_wp_page.patch
mm-khugepaged-remove-reuse_swap_page-usage.patch
mm-swapfile-remove-stale-reuse_swap_page.patch
mm-huge_memory-remove-stale-page_trans_huge_mapcount.patch
mm-huge_memory-remove-stale-locking-logic-from-__split_huge_pmd.patch
proc-vmcore-fix-possible-deadlock-on-concurrent-mmap-and-read.patch