From 4b91355e9dc9ac1eb3d69e56de093899ff2677ef Mon Sep 17 00:00:00 2001 From: KAMEZAWA Hiroyuki Date: Tue, 29 May 2012 15:06:51 -0700 Subject: memcg: fix/change behavior of shared anon at moving task This patch changes memcg's behavior at task_move(). At task_move(), the kernel scans a task's page table and move the changes for mapped pages from source cgroup to target cgroup. There has been a bug at handling shared anonymous pages for a long time. Before patch: - The spec says 'shared anonymous pages are not moved.' - The implementation was 'shared anonymoys pages may be moved'. If page_mapcount <=2, shared anonymous pages's charge were moved. After patch: - The spec says 'all anonymous pages are moved'. - The implementation is 'all anonymous pages are moved'. Considering usage of memcg, this will not affect user's experience. 'shared anonymous' pages only exists between a tree of processes which don't do exec(). Moving one of process without exec() seems not sane. For example, libcgroup will not be affected by this change. (Anyway, no one noticed the implementation for a long time...) Below is a discussion log: - current spec/implementation are complex - Now, shared file caches are moved - It adds unclear check as page_mapcount(). To do correct check, we should check swap users, etc. - No one notice this implementation behavior. So, no one get benefit from the design. - In general, once task is moved to a cgroup for running, it will not be moved.... - Finally, we have control knob as memory.move_charge_at_immigrate. Here is a patch to allow moving shared pages, completely. This makes memcg simpler and fix current broken code. Suggested-by: Hugh Dickins Signed-off-by: KAMEZAWA Hiroyuki Acked-by: Michal Hocko Cc: Johannes Weiner Cc: Naoya Horiguchi Cc: Glauber Costa Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- mm/memcontrol.c | 22 ++++++++++++++-------- 1 file changed, 14 insertions(+), 8 deletions(-) (limited to 'mm/memcontrol.c') diff --git a/mm/memcontrol.c b/mm/memcontrol.c index d7ce417cae7..e7db70f3d2d 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -5154,7 +5154,7 @@ static struct page *mc_handle_present_pte(struct vm_area_struct *vma, return NULL; if (PageAnon(page)) { /* we don't move shared anon */ - if (!move_anon() || page_mapcount(page) > 2) + if (!move_anon()) return NULL; } else if (!move_file()) /* we ignore mapcount for file pages */ @@ -5165,26 +5165,32 @@ static struct page *mc_handle_present_pte(struct vm_area_struct *vma, return page; } +#ifdef CONFIG_SWAP static struct page *mc_handle_swap_pte(struct vm_area_struct *vma, unsigned long addr, pte_t ptent, swp_entry_t *entry) { - int usage_count; struct page *page = NULL; swp_entry_t ent = pte_to_swp_entry(ptent); if (!move_anon() || non_swap_entry(ent)) return NULL; - usage_count = mem_cgroup_count_swap_user(ent, &page); - if (usage_count > 1) { /* we don't move shared anon */ - if (page) - put_page(page); - return NULL; - } + /* + * Because lookup_swap_cache() updates some statistics counter, + * we call find_get_page() with swapper_space directly. + */ + page = find_get_page(&swapper_space, ent.val); if (do_swap_account) entry->val = ent.val; return page; } +#else +static struct page *mc_handle_swap_pte(struct vm_area_struct *vma, + unsigned long addr, pte_t ptent, swp_entry_t *entry) +{ + return NULL; +} +#endif static struct page *mc_handle_file_pte(struct vm_area_struct *vma, unsigned long addr, pte_t ptent, swp_entry_t *entry) -- cgit v1.2.3-18-g5258