Commit 42cb14b1 authored by Hugh Dickins's avatar Hugh Dickins Committed by Linus Torvalds

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: default avatarHugh Dickins <hughd@google.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Davidlohr Bueso <dave@stgolabs.net>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Sasha Levin <sasha.levin@oracle.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent cf4b769a
...@@ -30,6 +30,7 @@ ...@@ -30,6 +30,7 @@
#include <linux/mempolicy.h> #include <linux/mempolicy.h>
#include <linux/vmalloc.h> #include <linux/vmalloc.h>
#include <linux/security.h> #include <linux/security.h>
#include <linux/backing-dev.h>
#include <linux/syscalls.h> #include <linux/syscalls.h>
#include <linux/hugetlb.h> #include <linux/hugetlb.h>
#include <linux/hugetlb_cgroup.h> #include <linux/hugetlb_cgroup.h>
...@@ -313,6 +314,8 @@ int migrate_page_move_mapping(struct address_space *mapping, ...@@ -313,6 +314,8 @@ int migrate_page_move_mapping(struct address_space *mapping,
struct buffer_head *head, enum migrate_mode mode, struct buffer_head *head, enum migrate_mode mode,
int extra_count) int extra_count)
{ {
struct zone *oldzone, *newzone;
int dirty;
int expected_count = 1 + extra_count; int expected_count = 1 + extra_count;
void **pslot; void **pslot;
...@@ -331,6 +334,9 @@ int migrate_page_move_mapping(struct address_space *mapping, ...@@ -331,6 +334,9 @@ int migrate_page_move_mapping(struct address_space *mapping,
return MIGRATEPAGE_SUCCESS; return MIGRATEPAGE_SUCCESS;
} }
oldzone = page_zone(page);
newzone = page_zone(newpage);
spin_lock_irq(&mapping->tree_lock); spin_lock_irq(&mapping->tree_lock);
pslot = radix_tree_lookup_slot(&mapping->page_tree, pslot = radix_tree_lookup_slot(&mapping->page_tree,
...@@ -378,6 +384,13 @@ int migrate_page_move_mapping(struct address_space *mapping, ...@@ -378,6 +384,13 @@ int migrate_page_move_mapping(struct address_space *mapping,
set_page_private(newpage, page_private(page)); 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); radix_tree_replace_slot(pslot, newpage);
/* /*
...@@ -387,6 +400,9 @@ int migrate_page_move_mapping(struct address_space *mapping, ...@@ -387,6 +400,9 @@ int migrate_page_move_mapping(struct address_space *mapping,
*/ */
page_unfreeze_refs(page, expected_count - 1); 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 * If moved to a different zone then also account
* the page for that zone. Other VM counters will be * the page for that zone. Other VM counters will be
...@@ -397,13 +413,19 @@ int migrate_page_move_mapping(struct address_space *mapping, ...@@ -397,13 +413,19 @@ int migrate_page_move_mapping(struct address_space *mapping,
* via NR_FILE_PAGES and NR_ANON_PAGES if they * via NR_FILE_PAGES and NR_ANON_PAGES if they
* are mapped to swap space. * are mapped to swap space.
*/ */
__dec_zone_page_state(page, NR_FILE_PAGES); if (newzone != oldzone) {
__inc_zone_page_state(newpage, NR_FILE_PAGES); __dec_zone_state(oldzone, NR_FILE_PAGES);
if (!PageSwapCache(page) && PageSwapBacked(page)) { __inc_zone_state(newzone, NR_FILE_PAGES);
__dec_zone_page_state(page, NR_SHMEM); if (PageSwapBacked(page) && !PageSwapCache(page)) {
__inc_zone_page_state(newpage, NR_SHMEM); __dec_zone_state(oldzone, NR_SHMEM);
__inc_zone_state(newzone, NR_SHMEM);
} }
spin_unlock_irq(&mapping->tree_lock); if (dirty && mapping_cap_account_dirty(mapping)) {
__dec_zone_state(oldzone, NR_FILE_DIRTY);
__inc_zone_state(newzone, NR_FILE_DIRTY);
}
}
local_irq_enable();
return MIGRATEPAGE_SUCCESS; return MIGRATEPAGE_SUCCESS;
} }
...@@ -524,20 +546,9 @@ void migrate_page_copy(struct page *newpage, struct page *page) ...@@ -524,20 +546,9 @@ void migrate_page_copy(struct page *newpage, struct page *page)
if (PageMappedToDisk(page)) if (PageMappedToDisk(page))
SetPageMappedToDisk(newpage); SetPageMappedToDisk(newpage);
if (PageDirty(page)) { /* Move dirty on pages not done by migrate_page_move_mapping() */
clear_page_dirty_for_io(page); if (PageDirty(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); SetPageDirty(newpage);
else
__set_page_dirty_nobuffers(newpage);
}
if (page_is_young(page)) if (page_is_young(page))
set_page_young(newpage); set_page_young(newpage);
......
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