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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The -mm tree is included into linux-next and is updated
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------------------------------------------------------
From: Yang Shi <shy828301@xxxxxxxxx>
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/bb27e3fe-6036-b637-5086-272befbfe3da@xxxxxxxxxx
Suggested-by: Hugh Dickins <hughd@xxxxxxxxxx>
Signed-off-by: Yang Shi <shy828301@xxxxxxxxx>
Acked-by: Minchan Kim <minchan@xxxxxxxxxx>
Reviewed-by: Shakeel Butt <shakeelb@xxxxxxxxxx>
Acked-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
Signed-off-by: Hugh Dickins <hughd@xxxxxxxxxx>
Acked-by: Naoya Horiguchi <naoya.horiguchi@xxxxxxx>
Cc: Alistair Popple <apopple@xxxxxxxxxx>
Cc: Jan Kara <jack@xxxxxxx>
Cc: Jue Wang <juew@xxxxxxxxxx>
Cc: "Matthew Wilcox (Oracle)" <willy@xxxxxxxxxxxxx>
Cc: Miaohe Lin <linmiaohe@xxxxxxxxxx>
Cc: Oscar Salvador <osalvador@xxxxxxx>
Cc: Peter Xu <peterx@xxxxxxxxxx>
Cc: Ralph Campbell <rcampbell@xxxxxxxxxx>
Cc: Wang Yugui <wangyugui@xxxxxxxxxxxx>
Cc: Zi Yan <ziy@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
include/linux/rmap.h | 2 +-
mm/memory-failure.c | 15 +++++++--------
mm/rmap.c | 15 ++++-----------
mm/vmscan.c | 3 ++-
4 files changed, 14 insertions(+), 21 deletions(-)
--- a/include/linux/rmap.h~mm-rmap-make-try_to_unmap-void-function
+++ a/include/linux/rmap.h
@@ -195,7 +195,7 @@ static inline void page_dup_rmap(struct
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)
--- a/mm/memory-failure.c~mm-rmap-make-try_to_unmap-void-function
+++ a/mm/memory-failure.c
@@ -1242,7 +1242,7 @@ 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);
@@ -1305,7 +1305,7 @@ 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)) {
/*
@@ -1317,17 +1317,16 @@ 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
@@ -1405,7 +1405,7 @@ static bool try_to_unmap_one(struct page
/*
* When racing against e.g. zap_pte_range() on another cpu,
* in between its ptep_get_and_clear_full() and page_remove_rmap(),
- * try_to_unmap() may return false when it is about to become true,
+ * try_to_unmap() may return before page_mapped() has become false,
* if page table locking is skipped: use TTU_SYNC to wait for that.
*/
if (flags & TTU_SYNC)
@@ -1756,9 +1756,10 @@ static int page_not_mapped(struct 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 caller's responsibility to check if the page is still
+ * mapped when needed (use TTU_SYNC to prevent accounting races).
*/
-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,
@@ -1783,14 +1784,6 @@ bool try_to_unmap(struct page *page, enu
rmap_walk_locked(page, &rwc);
else
rmap_walk(page, &rwc);
-
- /*
- * When racing against e.g. zap_pte_range() on another cpu,
- * in between its ptep_get_and_clear_full() and page_remove_rmap(),
- * try_to_unmap() may return false when it is about to become true,
- * if page table locking is skipped: use TTU_SYNC to wait for that.
- */
- return !page_mapcount(page);
}
/**
--- 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@xxxxxxxxx are
mm-thp-replace-debug_vm-bug-with-vm_warn-when-unmap-fails-for-split.patch
mm-mempolicy-dont-have-to-split-pmd-for-huge-zero-page.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
