The patch titled
Subject: mm: unmapped page migration avoid unmap+remap overhead
has been added to the -mm tree. Its filename is
mm-unmapped-page-migration-avoid-unmapremap-overhead.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/mm-unmapped-page-migration-avoid-unmapremap-overhead.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/mm-unmapped-page-migration-avoid-unmapremap-overhead.patch
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------------------------------------------------------
From: Hugh Dickins <hughd@xxxxxxxxxx>
Subject: mm: unmapped page migration avoid unmap+remap overhead
Page migration's __unmap_and_move(), and rmap's try_to_unmap(), were
created for use on pages almost certainly mapped into userspace. But
nowadays compaction often applies them to unmapped page cache pages: which
may exacerbate contention on i_mmap_rwsem quite unnecessarily, since
try_to_unmap_file() makes no preliminary page_mapped() check.
Now check page_mapped() in __unmap_and_move(); and avoid repeating the
same overhead in rmap_walk_file() - don't remove_migration_ptes() when we
never inserted any.
(The PageAnon(page) comment blocks now look even sillier than before, but
clean that up on some other occasion. And note in passing that
try_to_unmap_one() does not use a migration entry when PageSwapCache, so
remove_migration_ptes() will then not update that swap entry to newpage
pte: not a big deal, but something else to clean up later.)
Davidlohr remarked in "mm,fs: introduce helpers around the i_mmap_mutex"
conversion to i_mmap_rwsem, that "The biggest winner of these changes is
migration": a part of the reason might be all of that unnecessary taking
of i_mmap_mutex in page migration; and it's rather a shame that I didn't
get around to sending this patch in before his - this one is much less
useful after Davidlohr's conversion to rwsem, but still good.
Signed-off-by: Hugh Dickins <hughd@xxxxxxxxxx>
Cc: Davidlohr Bueso <dave@xxxxxxxxxxxx>
Cc: Rik van Riel <riel@xxxxxxxxxx>
Cc: Mel Gorman <mel@xxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/migrate.c | 28 ++++++++++++++++++----------
1 file changed, 18 insertions(+), 10 deletions(-)
diff -puN mm/migrate.c~mm-unmapped-page-migration-avoid-unmapremap-overhead mm/migrate.c
--- a/mm/migrate.c~mm-unmapped-page-migration-avoid-unmapremap-overhead
+++ a/mm/migrate.c
@@ -746,7 +746,7 @@ static int fallback_migrate_page(struct
* MIGRATEPAGE_SUCCESS - success
*/
static int move_to_new_page(struct page *newpage, struct page *page,
- int remap_swapcache, enum migrate_mode mode)
+ int page_was_mapped, enum migrate_mode mode)
{
struct address_space *mapping;
int rc;
@@ -784,7 +784,7 @@ static int move_to_new_page(struct page
newpage->mapping = NULL;
} else {
mem_cgroup_migrate(page, newpage, false);
- if (remap_swapcache)
+ if (page_was_mapped)
remove_migration_ptes(page, newpage);
page->mapping = NULL;
}
@@ -798,7 +798,7 @@ static int __unmap_and_move(struct page
int force, enum migrate_mode mode)
{
int rc = -EAGAIN;
- int remap_swapcache = 1;
+ int page_was_mapped = 0;
struct anon_vma *anon_vma = NULL;
if (!trylock_page(page)) {
@@ -870,7 +870,6 @@ static int __unmap_and_move(struct page
* migrated but are not remapped when migration
* completes
*/
- remap_swapcache = 0;
} else {
goto out_unlock;
}
@@ -910,13 +909,17 @@ static int __unmap_and_move(struct page
}
/* Establish migration ptes or remove ptes */
- try_to_unmap(page, TTU_MIGRATION|TTU_IGNORE_MLOCK|TTU_IGNORE_ACCESS);
+ if (page_mapped(page)) {
+ try_to_unmap(page,
+ TTU_MIGRATION|TTU_IGNORE_MLOCK|TTU_IGNORE_ACCESS);
+ page_was_mapped = 1;
+ }
skip_unmap:
if (!page_mapped(page))
- rc = move_to_new_page(newpage, page, remap_swapcache, mode);
+ rc = move_to_new_page(newpage, page, page_was_mapped, mode);
- if (rc && remap_swapcache)
+ if (rc && page_was_mapped)
remove_migration_ptes(page, page);
/* Drop an anon_vma reference if we took one */
@@ -1017,6 +1020,7 @@ static int unmap_and_move_huge_page(new_
{
int rc = 0;
int *result = NULL;
+ int page_was_mapped = 0;
struct page *new_hpage;
struct anon_vma *anon_vma = NULL;
@@ -1047,12 +1051,16 @@ static int unmap_and_move_huge_page(new_
if (PageAnon(hpage))
anon_vma = page_get_anon_vma(hpage);
- try_to_unmap(hpage, TTU_MIGRATION|TTU_IGNORE_MLOCK|TTU_IGNORE_ACCESS);
+ if (page_mapped(hpage)) {
+ try_to_unmap(hpage,
+ TTU_MIGRATION|TTU_IGNORE_MLOCK|TTU_IGNORE_ACCESS);
+ page_was_mapped = 1;
+ }
if (!page_mapped(hpage))
- rc = move_to_new_page(new_hpage, hpage, 1, mode);
+ rc = move_to_new_page(new_hpage, hpage, page_was_mapped, mode);
- if (rc != MIGRATEPAGE_SUCCESS)
+ if (rc != MIGRATEPAGE_SUCCESS && page_was_mapped)
remove_migration_ptes(hpage, hpage);
if (anon_vma)
_
Patches currently in -mm which might be from hughd@xxxxxxxxxx are
mm-vmscan-count-only-dirty-pages-as-congested.patch
mm-memcontrol-update-mem_cgroup_page_lruvec-documentation.patch
mm-memcontrol-clarify-migration-where-old-page-is-uncharged.patch
mm-memcontrol-uncharge-pages-on-swapout.patch
mm-memcontrol-uncharge-pages-on-swapout-fix.patch
mm-memcontrol-remove-unnecessary-pcg_memsw-memoryswap-charge-flag.patch
mm-memcontrol-remove-unnecessary-pcg_mem-memory-charge-flag.patch
mm-memcontrol-remove-unnecessary-pcg_used-pc-mem_cgroup-valid-flag.patch
mm-memcontrol-remove-unnecessary-pcg_used-pc-mem_cgroup-valid-flag-fix.patch
mmfs-introduce-helpers-around-the-i_mmap_mutex.patch
mm-use-new-helper-functions-around-the-i_mmap_mutex.patch
mm-convert-i_mmap_mutex-to-rwsem.patch
mm-rmap-share-the-i_mmap_rwsem.patch
uprobes-share-the-i_mmap_rwsem.patch
mm-xip-share-the-i_mmap_rwsem.patch
mm-memory-failure-share-the-i_mmap_rwsem.patch
mm-nommu-share-the-i_mmap_rwsem.patch
mm-memoryc-share-the-i_mmap_rwsem.patch
mm-mincore-add-hwpoison-page-handle.patch
ksm-replace-smp_read_barrier_depends-with-lockless_dereference.patch
mm-fix-anon_vma_clone-error-treatment.patch
mm-unmapped-page-migration-avoid-unmapremap-overhead.patch
linux-next.patch
mm-replace-remap_file_pages-syscall-with-emulation.patch
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