On Thu 28-06-12 19:23:11, KAMEZAWA Hiroyuki wrote:
> For handling many kinds of races, memcg adds an extra charge to
> page's memcg at page migration. But this affects the page compaction
> and make it fail if the memcg is under OOM.
>
> This patch uses res_counter_charge_nofail() in page migration path
> and remove -ENOMEM. By this, page migration will not fail by the
> status of memcg.
Maybe we could add something like below to the changelog as well.
"
Even though res_counter_charge_nofail can silently go over the memcg
limit mem_cgroup_usage compensates that and it doesn't tell the real truth
to the userspace.
Excessive charges are only temporal and done on a single page per-CPU in
the worst case. This sounds tolerable and actually consumes less charges
than the current per-cpu memcg_stock.
"
> Reported-by: David Rientjes <rientjes@xxxxxxxxxx>
> Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx>
Acked-by: Michal Hocko <mhocko@xxxxxxx>
Thanks!
> ---
> mm/memcontrol.c | 26 +++++++-------------------
> 1 files changed, 7 insertions(+), 19 deletions(-)
>
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index a2677e0..7424fab 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -3168,6 +3168,7 @@ int mem_cgroup_prepare_migration(struct page *page,
> struct page *newpage, struct mem_cgroup **memcgp, gfp_t gfp_mask)
> {
> struct mem_cgroup *memcg = NULL;
> + struct res_counter *dummy;
> struct page_cgroup *pc;
> enum charge_type ctype;
> int ret = 0;
> @@ -3222,29 +3223,16 @@ int mem_cgroup_prepare_migration(struct page *page,
> */
> if (!memcg)
> return 0;
> -
> - *memcgp = memcg;
> - ret = __mem_cgroup_try_charge(NULL, gfp_mask, 1, memcgp, false);
> - css_put(&memcg->css);/* drop extra refcnt */
> - if (ret) {
> - if (PageAnon(page)) {
> - lock_page_cgroup(pc);
> - ClearPageCgroupMigration(pc);
> - unlock_page_cgroup(pc);
> - /*
> - * The old page may be fully unmapped while we kept it.
> - */
> - mem_cgroup_uncharge_page(page);
> - }
> - /* we'll need to revisit this error code (we have -EINTR) */
> - return -ENOMEM;
> - }
> /*
> * We charge new page before it's used/mapped. So, even if unlock_page()
> * is called before end_migration, we can catch all events on this new
> * page. In the case new page is migrated but not remapped, new page's
> * mapcount will be finally 0 and we call uncharge in end_migration().
> */
> + res_counter_charge_nofail(&memcg->res, PAGE_SIZE, &dummy);
> + if (do_swap_account)
> + res_counter_charge_nofail(&memcg->memsw, PAGE_SIZE, &dummy);
> +
> if (PageAnon(page))
> ctype = MEM_CGROUP_CHARGE_TYPE_ANON;
> else if (page_is_file_cache(page))
> @@ -3807,9 +3795,9 @@ static inline u64 mem_cgroup_usage(struct mem_cgroup *memcg, bool swap)
>
> if (!mem_cgroup_is_root(memcg)) {
> if (!swap)
> - return res_counter_read_u64(&memcg->res, RES_USAGE);
> + return res_counter_usage_safe(&memcg->res);
> else
> - return res_counter_read_u64(&memcg->memsw, RES_USAGE);
> + return res_counter_usage_safe(&memcg->memsw);
> }
>
> val = mem_cgroup_recursive_stat(memcg, MEM_CGROUP_STAT_CACHE);
> --
> 1.7.4.1
>
>
--
Michal Hocko
SUSE Labs
SUSE LINUX s.r.o.
Lihovarska 1060/12
190 00 Praha 9
Czech Republic
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