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mm: page migration avoid touching newpage until no going back

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We have had trouble in the past from the way in which page migration's
newpage is initialized in dribs and drabs - see commit 8bdd638091 ("mm:
fix direct reclaim writeback regression") which proposed a cleanup.

We have no actual problem now, but I think the procedure would be clearer
(and alternative get_new_page pools safer to implement) if we assert that
newpage is not touched until we are sure that it's going to be used -
except for taking the trylock on it in __unmap_and_move().

So shift the early initializations from move_to_new_page() into
migrate_page_move_mapping(), mapping and NULL-mapping paths.  Similarly
migrate_huge_page_move_mapping(), but its NULL-mapping path can just be
deleted: you cannot reach hugetlbfs_migrate_page() with a NULL mapping.

Adjust stages 3 to 8 in the Documentation file accordingly.

Signed-off-by: Hugh 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: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Hugh Dickins
2015-11-05 18:50:02 -08:00
committed by Linus Torvalds
parent 470f119f01
commit cf4b769abb
2 changed files with 30 additions and 38 deletions
Download Patch File Download Diff File Expand all files Collapse all files

49
mm/migrate.c
View File

@@ -320,6 +320,14 @@ int migrate_page_move_mapping(struct address_space *mapping,
/* Anonymous page without mapping */
if (page_count(page) != expected_count)
return -EAGAIN;
/* No turning back from here */
set_page_memcg(newpage, page_memcg(page));
newpage->index = page->index;
newpage->mapping = page->mapping;
if (PageSwapBacked(page))
SetPageSwapBacked(newpage);
return MIGRATEPAGE_SUCCESS;
}
@@ -355,8 +363,15 @@ int migrate_page_move_mapping(struct address_space *mapping,
}
/*
* Now we know that no one else is looking at the page.
* Now we know that no one else is looking at the page:
* no turning back from here.
*/
set_page_memcg(newpage, page_memcg(page));
newpage->index = page->index;
newpage->mapping = page->mapping;
if (PageSwapBacked(page))
SetPageSwapBacked(newpage);
get_page(newpage); /* add cache reference */
if (PageSwapCache(page)) {
SetPageSwapCache(newpage);
@@ -403,12 +418,6 @@ int migrate_huge_page_move_mapping(struct address_space *mapping,
int expected_count;
void **pslot;
if (!mapping) {
if (page_count(page) != 1)
return -EAGAIN;
return MIGRATEPAGE_SUCCESS;
}
spin_lock_irq(&mapping->tree_lock);
pslot = radix_tree_lookup_slot(&mapping->page_tree,
@@ -426,6 +435,9 @@ int migrate_huge_page_move_mapping(struct address_space *mapping,
return -EAGAIN;
}
set_page_memcg(newpage, page_memcg(page));
newpage->index = page->index;
newpage->mapping = page->mapping;
get_page(newpage);
radix_tree_replace_slot(pslot, newpage);
@@ -730,21 +742,6 @@ static int move_to_new_page(struct page *newpage, struct page *page,
VM_BUG_ON_PAGE(!PageLocked(page), page);
VM_BUG_ON_PAGE(!PageLocked(newpage), newpage);
/* Prepare mapping for the new page.*/
newpage->index = page->index;
newpage->mapping = page->mapping;
if (PageSwapBacked(page))
SetPageSwapBacked(newpage);
/*
* Indirectly called below, migrate_page_copy() copies PG_dirty and thus
* needs newpage's memcg set to transfer memcg dirty page accounting.
* So perform memcg migration in two steps:
* 1. set newpage->mem_cgroup (here)
* 2. clear page->mem_cgroup (below)
*/
set_page_memcg(newpage, page_memcg(page));
mapping = page_mapping(page);
if (!mapping)
rc = migrate_page(mapping, newpage, page, mode);
@@ -767,9 +764,6 @@ static int move_to_new_page(struct page *newpage, struct page *page,
set_page_memcg(page, NULL);
if (!PageAnon(page))
page->mapping = NULL;
} else {
set_page_memcg(newpage, NULL);
newpage->mapping = NULL;
}
return rc;
}
@@ -971,10 +965,9 @@ out:
* it. Otherwise, putback_lru_page() will drop the reference grabbed
* during isolation.
*/
if (put_new_page) {
ClearPageSwapBacked(newpage);
if (put_new_page)
put_new_page(newpage, private);
} else if (unlikely(__is_movable_balloon_page(newpage))) {
else if (unlikely(__is_movable_balloon_page(newpage))) {
/* drop our reference, page already in the balloon */
put_page(newpage);
} else