mm-khugepaged-remove-reuse_swap_page-usage.patch removed from -mm tree

The patch titled
Subject: mm/khugepaged: remove reuse_swap_page() usage
has been removed from the -mm tree. Its filename was
mm-khugepaged-remove-reuse_swap_page-usage.patch

This patch was dropped because it was merged into mainline or a subsystem tree

------------------------------------------------------
From: David Hildenbrand <[email protected]>
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().

---

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

@@ -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")	\

@@ -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 [email protected] are