Messages in this thread Patch in this message | | | Date | Wed, 17 Sep 2008 13:31:49 +0900 | From | Daisuke Nishimura <> | Subject | [PATCH -mm] memcg: fix handling of shmem migration |
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PG_swapbacked flag of newpage should be set(if needed) before mem_cgroup_prepare_migration, because mem_cgroup_charge_common checks the flag and determines whether it sets PAGE_CGROUP_FLAG_FILE or not.
Before this patch, if migrating shmem/tmpfs pages, newpage would be charged with PAGE_CGROUP_FLAG_FILE set, while oldpage has been charged without the flag.
The problem here is mem_cgroup_move_lists doesn't clear(or set) the PAGE_CGROUP_FLAG_FILE flag, so pc->flags of the newpage remains PAGE_CGROUP_FLAG_FILE set even when the pc is moved to another lru(anon) by mem_cgroup_move_lists. And this leads to incorrect MEM_CGROUP_ZSTAT. (In my test, I see an underflow of MEM_CGROUP_ZSTAT(active_file). As a result, mem_cgroup_calc_reclaim returns very huge number and causes soft lockup on page reclaim.)
I'm not sure if mem_cgroup_move_lists should handle PAGE_CGROUP_FLAG_FILE or not(I suppose it should be used to move between active <-> inactive, not anon <-> file), I moved SetPageSwapBacked(newpage) before mem_cgroup_prepare_migration.
Signed-off-by: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp> --- mm/migrate.c | 4 ++-- 1 files changed, 2 insertions(+), 2 deletions(-)
diff --git a/mm/migrate.c b/mm/migrate.c index 577d481..7343463 100644 --- a/mm/migrate.c +++ b/mm/migrate.c @@ -586,8 +586,6 @@ static int move_to_new_page(struct page *newpage, struct page *page) /* Prepare mapping for the new page.*/ newpage->index = page->index; newpage->mapping = page->mapping; - if (PageSwapBacked(page)) - SetPageSwapBacked(newpage); mapping = page_mapping(page); if (!mapping) @@ -636,6 +634,8 @@ static int unmap_and_move(new_page_t get_new_page, unsigned long private, goto move_newpage; } + if (PageSwapBacked(page)) + SetPageSwapBacked(newpage); charge = mem_cgroup_prepare_migration(page, newpage); if (charge == -ENOMEM) { rc = -ENOMEM;
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