The patch titled
Subject: mm: migrate dirty page without clear_page_dirty_for_io etc
has been added to the -mm tree. Its filename is
mm-migrate-dirty-page-without-clear_page_dirty_for_io-etc.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/mm-migrate-dirty-page-without-clear_page_dirty_for_io-etc.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/mm-migrate-dirty-page-without-clear_page_dirty_for_io-etc.patch
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------------------------------------------------------
From: Hugh Dickins <hughd@xxxxxxxxxx>
Subject: mm: migrate dirty page without clear_page_dirty_for_io etc
clear_page_dirty_for_io() has accumulated writeback and memcg subtleties
since v2.6.16 first introduced page migration; and the set_page_dirty()
which completed its migration of PageDirty, later had to be moderated to
__set_page_dirty_nobuffers(); then PageSwapBacked had to skip that too.
No actual problems seen with this procedure recently, but if you look into
what the clear_page_dirty_for_io(page)+set_page_dirty(newpage) is actually
achieving, it turns out to be nothing more than moving the PageDirty flag,
and its NR_FILE_DIRTY stat from one zone to another.
It would be good to avoid a pile of irrelevant decrementations and
incrementations, and improper event counting, and unnecessary descent of
the radix_tree under tree_lock (to set the PAGECACHE_TAG_DIRTY which
radix_tree_replace_slot() left in place anyway).
Do the NR_FILE_DIRTY movement, like the other stats movements, while
interrupts still disabled in migrate_page_move_mapping(); and don't even
bother if the zone is the same. Do the PageDirty movement there under
tree_lock too, where old page is frozen and newpage not yet visible:
bearing in mind that as soon as newpage becomes visible in radix_tree, an
un-page-locked set_page_dirty() might interfere (or perhaps that's just
not possible: anything doing so should already hold an additional
reference to the old page, preventing its migration; but play safe).
But we do still need to transfer PageDirty in migrate_page_copy(), for
those who don't go the mapping route through migrate_page_move_mapping().
Signed-off-by: Hugh Dickins <hughd@xxxxxxxxxx>
Cc: Christoph Lameter <cl@xxxxxxxxx>
Cc: "Kirill A. Shutemov" <kirill.shutemov@xxxxxxxxxxxxxxx>
Cc: Rik van Riel <riel@xxxxxxxxxx>
Cc: Vlastimil Babka <vbabka@xxxxxxx>
Cc: Davidlohr Bueso <dave@xxxxxxxxxxxx>
Cc: Oleg Nesterov <oleg@xxxxxxxxxx>
Cc: Sasha Levin <sasha.levin@xxxxxxxxxx>
Cc: Andrey Konovalov <andreyknvl@xxxxxxxxxx>
Cc: Dmitry Vyukov <dvyukov@xxxxxxxxxx>
Cc: KOSAKI Motohiro <kosaki.motohiro@xxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/migrate.c | 51 +++++++++++++++++++++++++++++--------------------
1 file changed, 31 insertions(+), 20 deletions(-)
diff -puN mm/migrate.c~mm-migrate-dirty-page-without-clear_page_dirty_for_io-etc mm/migrate.c
--- a/mm/migrate.c~mm-migrate-dirty-page-without-clear_page_dirty_for_io-etc
+++ a/mm/migrate.c
@@ -30,6 +30,7 @@
#include <linux/mempolicy.h>
#include <linux/vmalloc.h>
#include <linux/security.h>
+#include <linux/backing-dev.h>
#include <linux/syscalls.h>
#include <linux/hugetlb.h>
#include <linux/hugetlb_cgroup.h>
@@ -313,6 +314,8 @@ int migrate_page_move_mapping(struct add
struct buffer_head *head, enum migrate_mode mode,
int extra_count)
{
+ struct zone *oldzone, *newzone;
+ int dirty;
int expected_count = 1 + extra_count;
void **pslot;
@@ -331,6 +334,9 @@ int migrate_page_move_mapping(struct add
return MIGRATEPAGE_SUCCESS;
}
+ oldzone = page_zone(page);
+ newzone = page_zone(newpage);
+
spin_lock_irq(&mapping->tree_lock);
pslot = radix_tree_lookup_slot(&mapping->page_tree,
@@ -378,6 +384,13 @@ int migrate_page_move_mapping(struct add
set_page_private(newpage, page_private(page));
}
+ /* Move dirty while page refs frozen and newpage not yet exposed */
+ dirty = PageDirty(page);
+ if (dirty) {
+ ClearPageDirty(page);
+ SetPageDirty(newpage);
+ }
+
radix_tree_replace_slot(pslot, newpage);
/*
@@ -387,6 +400,9 @@ int migrate_page_move_mapping(struct add
*/
page_unfreeze_refs(page, expected_count - 1);
+ spin_unlock(&mapping->tree_lock);
+ /* Leave irq disabled to prevent preemption while updating stats */
+
/*
* If moved to a different zone then also account
* the page for that zone. Other VM counters will be
@@ -397,13 +413,19 @@ int migrate_page_move_mapping(struct add
* via NR_FILE_PAGES and NR_ANON_PAGES if they
* are mapped to swap space.
*/
- __dec_zone_page_state(page, NR_FILE_PAGES);
- __inc_zone_page_state(newpage, NR_FILE_PAGES);
- if (!PageSwapCache(page) && PageSwapBacked(page)) {
- __dec_zone_page_state(page, NR_SHMEM);
- __inc_zone_page_state(newpage, NR_SHMEM);
+ if (newzone != oldzone) {
+ __dec_zone_state(oldzone, NR_FILE_PAGES);
+ __inc_zone_state(newzone, NR_FILE_PAGES);
+ if (PageSwapBacked(page) && !PageSwapCache(page)) {
+ __dec_zone_state(oldzone, NR_SHMEM);
+ __inc_zone_state(newzone, NR_SHMEM);
+ }
+ if (dirty && mapping_cap_account_dirty(mapping)) {
+ __dec_zone_state(oldzone, NR_FILE_DIRTY);
+ __inc_zone_state(newzone, NR_FILE_DIRTY);
+ }
}
- spin_unlock_irq(&mapping->tree_lock);
+ local_irq_enable();
return MIGRATEPAGE_SUCCESS;
}
@@ -524,20 +546,9 @@ void migrate_page_copy(struct page *newp
if (PageMappedToDisk(page))
SetPageMappedToDisk(newpage);
- if (PageDirty(page)) {
- clear_page_dirty_for_io(page);
- /*
- * Want to mark the page and the radix tree as dirty, and
- * redo the accounting that clear_page_dirty_for_io undid,
- * but we can't use set_page_dirty because that function
- * is actually a signal that all of the page has become dirty.
- * Whereas only part of our page may be dirty.
- */
- if (PageSwapBacked(page))
- SetPageDirty(newpage);
- else
- __set_page_dirty_nobuffers(newpage);
- }
+ /* Move dirty on pages not done by migrate_page_move_mapping() */
+ if (PageDirty(page))
+ SetPageDirty(newpage);
if (page_is_young(page))
set_page_young(newpage);
_
Patches currently in -mm which might be from hughd@xxxxxxxxxx are
memcg-simplify-and-inline-__mem_cgroup_from_kmem-fix-2.patch
mm-documentation-undoc-non-linear-vmas.patch
mm-rmap-use-pte-lock-not-mmap_sem-to-set-pagemlocked.patch
mm-page-migration-fix-pagemlocked-on-migrated-pages.patch
mm-rename-mem_cgroup_migrate-to-mem_cgroup_replace_page.patch
mm-correct-a-couple-of-page-migration-comments.patch
mm-page-migration-use-the-put_new_page-whenever-necessary.patch
mm-page-migration-trylock-newpage-at-same-level-as-oldpage.patch
mm-page-migration-remove_migration_ptes-at-lockunlock-level.patch
mm-simplify-page-migrations-anon_vma-comment-and-flow.patch
mm-page-migration-use-migration-entry-for-swapcache-too.patch
mm-page-migration-avoid-touching-newpage-until-no-going-back.patch
mm-migrate-dirty-page-without-clear_page_dirty_for_io-etc.patch
mm-use-unsigned-int-for-page-order-fix-2.patch
mm-dont-split-thp-page-when-syscall-is-called-fix-4.patch
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