+ mm-rmap-make-try_to_unmap-void-function.patch added to -mm tree

* + mm-rmap-make-try_to_unmap-void-function.patch added to -mm tree
@ 2021-05-26 20:28 akpm
  0 siblings, 0 replies; 2+ messages in thread
From: akpm @ 2021-05-26 20:28 UTC (permalink / raw)
  To: hughd, mm-commits, shy828301


The patch titled
     Subject: mm: rmap: make try_to_unmap() void function
has been added to the -mm tree.  Its filename is
     mm-rmap-make-try_to_unmap-void-function.patch

This patch should soon appear at
    https://ozlabs.org/~akpm/mmots/broken-out/mm-rmap-make-try_to_unmap-void-function.patch
and later at
    https://ozlabs.org/~akpm/mmotm/broken-out/mm-rmap-make-try_to_unmap-void-function.patch

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*** Remember to use Documentation/process/submit-checklist.rst when testing your code ***

The -mm tree is included into linux-next and is updated
there every 3-4 working days

------------------------------------------------------
From: Yang Shi <shy828301@gmail.com>
Subject: mm: rmap: make try_to_unmap() void function

Currently try_to_unmap() return bool value by checking page_mapcount(),
however this may return false positive since page_mapcount() doesn't
check all subpages of compound page.  The total_mapcount() could be used
instead, but its cost is higher since it traverses all subpages.

Actually the most callers of try_to_unmap() don't care about the
return value at all.  So just need check if page is still mapped by
page_mapped() when necessary.  And page_mapped() does bail out early
when it finds mapped subpage.

Link: https://lkml.kernel.org/r/20210526201239.3351-2-shy828301@gmail.com
Suggested-by: Hugh Dickins <hughd@google.com>
Acked-by: Hugh Dickins <hughd@google.com>
Signed-off-by: Yang Shi <shy828301@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 include/linux/rmap.h |    2 +-
 mm/memory-failure.c  |   15 +++++++--------
 mm/rmap.c            |    7 +++----
 mm/vmscan.c          |    3 ++-
 4 files changed, 13 insertions(+), 14 deletions(-)

--- a/include/linux/rmap.h~mm-rmap-make-try_to_unmap-void-function
+++ a/include/linux/rmap.h
@@ -191,7 +191,7 @@ int page_referenced(struct page *, int i
 			struct mem_cgroup *memcg, unsigned long *vm_flags);
 
 bool try_to_migrate(struct page *page, enum ttu_flags flags);
-bool try_to_unmap(struct page *, enum ttu_flags flags);
+void try_to_unmap(struct page *, enum ttu_flags flags);
 
 int make_device_exclusive_range(struct mm_struct *mm, unsigned long start,
 				unsigned long end, struct page **pages,
--- a/mm/memory-failure.c~mm-rmap-make-try_to_unmap-void-function
+++ a/mm/memory-failure.c
@@ -1206,7 +1206,7 @@ static bool hwpoison_user_mappings(struc
 	enum ttu_flags ttu = TTU_IGNORE_MLOCK;
 	struct address_space *mapping;
 	LIST_HEAD(tokill);
-	bool unmap_success = true;
+	bool unmap_success;
 	int kill = 1, forcekill;
 	struct page *hpage = *hpagep;
 	bool mlocked = PageMlocked(hpage);
@@ -1269,7 +1269,7 @@ static bool hwpoison_user_mappings(struc
 		collect_procs(hpage, &tokill, flags & MF_ACTION_REQUIRED);
 
 	if (!PageHuge(hpage)) {
-		unmap_success = try_to_unmap(hpage, ttu);
+		try_to_unmap(hpage, ttu);
 	} else {
 		if (!PageAnon(hpage)) {
 			/*
@@ -1281,17 +1281,16 @@ static bool hwpoison_user_mappings(struc
 			 */
 			mapping = hugetlb_page_mapping_lock_write(hpage);
 			if (mapping) {
-				unmap_success = try_to_unmap(hpage,
-						     ttu|TTU_RMAP_LOCKED);
+				try_to_unmap(hpage, ttu|TTU_RMAP_LOCKED);
 				i_mmap_unlock_write(mapping);
-			} else {
+			} else
 				pr_info("Memory failure: %#lx: could not lock mapping for mapped huge page\n", pfn);
-				unmap_success = false;
-			}
 		} else {
-			unmap_success = try_to_unmap(hpage, ttu);
+			try_to_unmap(hpage, ttu);
 		}
 	}
+
+	unmap_success = !page_mapped(hpage);
 	if (!unmap_success)
 		pr_err("Memory failure: %#lx: failed to unmap page (mapcount=%d)\n",
 		       pfn, page_mapcount(hpage));
--- a/mm/rmap.c~mm-rmap-make-try_to_unmap-void-function
+++ a/mm/rmap.c
@@ -1660,9 +1660,10 @@ static int page_not_mapped(struct page *
  * page and the compound page it belongs to, used in the pageout path.
  * Caller must hold the page lock.
  *
- * If unmap is successful, return true. Otherwise, false.
+ * It is the callers' responsibility to check if the page is still
+ * mapped when needed.
  */
-bool try_to_unmap(struct page *page, enum ttu_flags flags)
+void try_to_unmap(struct page *page, enum ttu_flags flags)
 {
 	struct rmap_walk_control rwc = {
 		.rmap_one = try_to_unmap_one,
@@ -1948,8 +1949,6 @@ bool try_to_migrate(struct page *page, e
 		rmap_walk_locked(page, &rwc);
 	else
 		rmap_walk(page, &rwc);
-
-	return !page_mapcount(page) ? true : false;
 }
 
 /*
--- a/mm/vmscan.c~mm-rmap-make-try_to_unmap-void-function
+++ a/mm/vmscan.c
@@ -1499,7 +1499,8 @@ static unsigned int shrink_page_list(str
 			if (unlikely(PageTransHuge(page)))
 				flags |= TTU_SPLIT_HUGE_PMD;
 
-			if (!try_to_unmap(page, flags)) {
+			try_to_unmap(page, flags);
+			if (page_mapped(page)) {
 				stat->nr_unmap_fail += nr_pages;
 				if (!was_swapbacked && PageSwapBacked(page))
 					stat->nr_lazyfree_fail += nr_pages;
_

Patches currently in -mm which might be from shy828301@gmail.com are

mm-thp-check-total_mapcount-instead-of-page_mapcount.patch
mm-memory-add-orig_pmd-to-struct-vm_fault.patch
mm-memory-make-numa_migrate_prep-non-static.patch
mm-thp-refactor-numa-fault-handling.patch
mm-migrate-account-thp-numa-migration-counters-correctly.patch
mm-migrate-dont-split-thp-for-misplaced-numa-page.patch
mm-migrate-check-mapcount-for-thp-instead-of-refcount.patch
mm-thp-skip-make-pmd-prot_none-if-thp-migration-is-not-supported.patch
mm-rmap-make-try_to_unmap-void-function.patch


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