[v4 PATCH 2/2] mm: rmap: make try_to_unmap() void function
From: Yang Shi <hidden>
Date: 2021-05-26 20:12:51
Also in:
lkml
Subsystem:
hwpoison memory failure handling, memory management, memory management - mglru (multi-gen lru), memory management - reclaim, memory management - rmap (reverse mapping), the rest · Maintainers:
Miaohe Lin, Andrew Morton, Johannes Weiner, David Hildenbrand, Lorenzo Stoakes, Linus Torvalds
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.
Suggested-by: Hugh Dickins <hughd@google.com>
Acked-by: Hugh Dickins <hughd@google.com>
Signed-off-by: Yang Shi <redacted>
---
v4: Updated the comment of try_to_unmap() per Minchan.
Minor fix and patch reorder per Hugh.
Collected ack tag from Hugh.
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(-)
diff --git a/include/linux/rmap.h b/include/linux/rmap.h
index def5c62c93b3..116cb193110a 100644
--- a/include/linux/rmap.h
+++ b/include/linux/rmap.h@@ -194,7 +194,7 @@ static inline void page_dup_rmap(struct page *page, bool compound) int page_referenced(struct page *, int is_locked, struct mem_cgroup *memcg, unsigned long *vm_flags); -bool try_to_unmap(struct page *, enum ttu_flags flags); +void try_to_unmap(struct page *, enum ttu_flags flags); /* Avoid racy checks */ #define PVMW_SYNC (1 << 0)
diff --git a/mm/memory-failure.c b/mm/memory-failure.c
index 9dcc9bcea731..07e462588df9 100644
--- a/mm/memory-failure.c
+++ b/mm/memory-failure.c@@ -1063,7 +1063,7 @@ static bool hwpoison_user_mappings(struct page *p, unsigned long pfn, 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);
@@ -1126,7 +1126,7 @@ static bool hwpoison_user_mappings(struct page *p, unsigned long pfn, 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)) { /*
@@ -1138,17 +1138,16 @@ static bool hwpoison_user_mappings(struct page *p, unsigned long pfn, */ 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));
diff --git a/mm/rmap.c b/mm/rmap.c
index a35cbbbded0d..d4e0d89726b8 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c@@ -1749,9 +1749,10 @@ static int page_not_mapped(struct page *page) * Tries to remove all the page table entries which are mapping this * page, 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,
@@ -1776,8 +1777,6 @@ bool try_to_unmap(struct page *page, enum ttu_flags flags) rmap_walk_locked(page, &rwc); else rmap_walk(page, &rwc); - - return !page_mapcount(page) ? true : false; } /**
diff --git a/mm/vmscan.c b/mm/vmscan.c
index f96d62159720..fa5052ace415 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c@@ -1499,7 +1499,8 @@ static unsigned int shrink_page_list(struct list_head *page_list, 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;
--
2.26.2