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SubjectRe: [PATCH v5] memcg: remove PCG_CACHE page_cgroup flag
On Wed 25-01-12 14:41:00, KAMEZAWA Hiroyuki wrote:
[...]
> Subject: [PATCH v5] memcg: remove PCG_CACHE
>
> We record 'the page is cache' by PCG_CACHE bit to page_cgroup.
> Here, "CACHE" means anonymous user pages (and SwapCache). This
> doesn't include shmem.
>
> Consdering callers, at charge/uncharge, the caller should know
> what the page is and we don't need to record it by using 1bit
> per page.
>
> This patch removes PCG_CACHE bit and make callers of
> mem_cgroup_charge_statistics() to specify what the page is.
>
> About page migration:
> Mapping of the used page is not touched during migration (see
> page_remove_rmap) so we can rely on it and push the correct charge type
> down to __mem_cgroup_uncharge_common from end_migration for unused page.
> The force flag was misleading was abused for skipping the needless
> page_mapped() / PageCgroupMigration() check, as we know the unused page
> is no longer mapped and cleared the migration flag just a few lines
> up. But doing the checks is no biggie and it's not worth adding another
> flag just to skip them.
>
> Changelog since v4
> - fixed a bug at page migration by Michal Hokko.

Would be more fair:
- fixed a bug at page migration by Johannes Weiner

> Changelog since v3
> - renamed a variable 'rss' to 'anon'
>
> Changelog since v2
> - removed 'not_rss', added 'anon'
> - changed a meaning of arguments to mem_cgroup_charge_statisitcs()
> - removed a patch to mem_cgroup_uncharge_cache
> - simplified comment.
>
> Changelog since RFC.
> - rebased onto memcg-devel
> - rename 'file' to 'not_rss'
> - some cleanup and added comment.
>
> Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>

Anyway it looks good now (unless I missed something ;)).

Acked-by: Michal Hocko <mhocko@suse.cz>

> ---
> include/linux/page_cgroup.h | 8 +-----
> mm/memcontrol.c | 57 ++++++++++++++++++++++++-------------------
> 2 files changed, 33 insertions(+), 32 deletions(-)
>
> diff --git a/include/linux/page_cgroup.h b/include/linux/page_cgroup.h
> index a2d1177..1060292 100644
> --- a/include/linux/page_cgroup.h
> +++ b/include/linux/page_cgroup.h
> @@ -4,7 +4,6 @@
> enum {
> /* flags for mem_cgroup */
> PCG_LOCK, /* Lock for pc->mem_cgroup and following bits. */
> - PCG_CACHE, /* charged as cache */
> PCG_USED, /* this object is in use. */
> PCG_MIGRATION, /* under page migration */
> /* flags for mem_cgroup and file and I/O status */
> @@ -64,11 +63,6 @@ static inline void ClearPageCgroup##uname(struct page_cgroup *pc) \
> static inline int TestClearPageCgroup##uname(struct page_cgroup *pc) \
> { return test_and_clear_bit(PCG_##lname, &pc->flags); }
>
> -/* Cache flag is set only once (at allocation) */
> -TESTPCGFLAG(Cache, CACHE)
> -CLEARPCGFLAG(Cache, CACHE)
> -SETPCGFLAG(Cache, CACHE)
> -
> TESTPCGFLAG(Used, USED)
> CLEARPCGFLAG(Used, USED)
> SETPCGFLAG(Used, USED)
> @@ -85,7 +79,7 @@ static inline void lock_page_cgroup(struct page_cgroup *pc)
> {
> /*
> * Don't take this lock in IRQ context.
> - * This lock is for pc->mem_cgroup, USED, CACHE, MIGRATION
> + * This lock is for pc->mem_cgroup, USED, MIGRATION
> */
> bit_spin_lock(PCG_LOCK, &pc->flags);
> }
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index 1c56c5f..45dab06 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -670,15 +670,19 @@ static unsigned long mem_cgroup_read_events(struct mem_cgroup *memcg,
> }
>
> static void mem_cgroup_charge_statistics(struct mem_cgroup *memcg,
> - bool file, int nr_pages)
> + bool anon, int nr_pages)
> {
> preempt_disable();
>
> - if (file)
> - __this_cpu_add(memcg->stat->count[MEM_CGROUP_STAT_CACHE],
> + /*
> + * Here, RSS means 'mapped anon' and anon's SwapCache. Shmem/tmpfs is
> + * counted as CACHE even if it's on ANON LRU.
> + */
> + if (anon)
> + __this_cpu_add(memcg->stat->count[MEM_CGROUP_STAT_RSS],
> nr_pages);
> else
> - __this_cpu_add(memcg->stat->count[MEM_CGROUP_STAT_RSS],
> + __this_cpu_add(memcg->stat->count[MEM_CGROUP_STAT_CACHE],
> nr_pages);
>
> /* pagein of a big page is an event. So, ignore page size */
> @@ -2405,6 +2409,8 @@ static void __mem_cgroup_commit_charge(struct mem_cgroup *memcg,
> struct page_cgroup *pc,
> enum charge_type ctype)
> {
> + bool anon;
> +
> lock_page_cgroup(pc);
> if (unlikely(PageCgroupUsed(pc))) {
> unlock_page_cgroup(pc);
> @@ -2424,21 +2430,14 @@ static void __mem_cgroup_commit_charge(struct mem_cgroup *memcg,
> * See mem_cgroup_add_lru_list(), etc.
> */
> smp_wmb();
> - switch (ctype) {
> - case MEM_CGROUP_CHARGE_TYPE_CACHE:
> - case MEM_CGROUP_CHARGE_TYPE_SHMEM:
> - SetPageCgroupCache(pc);
> - SetPageCgroupUsed(pc);
> - break;
> - case MEM_CGROUP_CHARGE_TYPE_MAPPED:
> - ClearPageCgroupCache(pc);
> - SetPageCgroupUsed(pc);
> - break;
> - default:
> - break;
> - }
>
> - mem_cgroup_charge_statistics(memcg, PageCgroupCache(pc), nr_pages);
> + SetPageCgroupUsed(pc);
> + if (ctype == MEM_CGROUP_CHARGE_TYPE_MAPPED)
> + anon = true;
> + else
> + anon = false;
> +
> + mem_cgroup_charge_statistics(memcg, anon, nr_pages);
> unlock_page_cgroup(pc);
> WARN_ON_ONCE(PageLRU(page));
> /*
> @@ -2503,6 +2502,7 @@ static int mem_cgroup_move_account(struct page *page,
> {
> unsigned long flags;
> int ret;
> + bool anon = PageAnon(page);
>
> VM_BUG_ON(from == to);
> VM_BUG_ON(PageLRU(page));
> @@ -2531,14 +2531,14 @@ static int mem_cgroup_move_account(struct page *page,
> __this_cpu_inc(to->stat->count[MEM_CGROUP_STAT_FILE_MAPPED]);
> preempt_enable();
> }
> - mem_cgroup_charge_statistics(from, PageCgroupCache(pc), -nr_pages);
> + mem_cgroup_charge_statistics(from, anon, -nr_pages);
> if (uncharge)
> /* This is not "cancel", but cancel_charge does all we need. */
> __mem_cgroup_cancel_charge(from, nr_pages);
>
> /* caller should have done css_get */
> pc->mem_cgroup = to;
> - mem_cgroup_charge_statistics(to, PageCgroupCache(pc), nr_pages);
> + mem_cgroup_charge_statistics(to, anon, nr_pages);
> /*
> * We charges against "to" which may not have any tasks. Then, "to"
> * can be under rmdir(). But in current implementation, caller of
> @@ -2884,6 +2884,7 @@ __mem_cgroup_uncharge_common(struct page *page, enum charge_type ctype)
> struct mem_cgroup *memcg = NULL;
> unsigned int nr_pages = 1;
> struct page_cgroup *pc;
> + bool anon;
>
> if (mem_cgroup_disabled())
> return NULL;
> @@ -2915,6 +2916,7 @@ __mem_cgroup_uncharge_common(struct page *page, enum charge_type ctype)
> /* See mem_cgroup_prepare_migration() */
> if (page_mapped(page) || PageCgroupMigration(pc))
> goto unlock_out;
> + anon = true;
> break;
> case MEM_CGROUP_CHARGE_TYPE_SWAPOUT:
> if (!PageAnon(page)) { /* Shared memory */
> @@ -2922,12 +2924,14 @@ __mem_cgroup_uncharge_common(struct page *page, enum charge_type ctype)
> goto unlock_out;
> } else if (page_mapped(page)) /* Anon */
> goto unlock_out;
> + anon = true;
> break;
> default:
> + anon = false;
> break;
> }
>
> - mem_cgroup_charge_statistics(memcg, PageCgroupCache(pc), -nr_pages);
> + mem_cgroup_charge_statistics(memcg, anon, -nr_pages);
>
> ClearPageCgroupUsed(pc);
> /*
> @@ -3251,6 +3255,7 @@ void mem_cgroup_end_migration(struct mem_cgroup *memcg,
> {
> struct page *used, *unused;
> struct page_cgroup *pc;
> + bool anon;
>
> if (!memcg)
> return;
> @@ -3272,8 +3277,10 @@ void mem_cgroup_end_migration(struct mem_cgroup *memcg,
> lock_page_cgroup(pc);
> ClearPageCgroupMigration(pc);
> unlock_page_cgroup(pc);
> -
> - __mem_cgroup_uncharge_common(unused, MEM_CGROUP_CHARGE_TYPE_FORCE);
> + anon = PageAnon(used);
> + __mem_cgroup_uncharge_common(unused,
> + anon ? MEM_CGROUP_CHARGE_TYPE_MAPPED
> + : MEM_CGROUP_CHARGE_TYPE_CACHE);
>
> /*
> * If a page is a file cache, radix-tree replacement is very atomic
> @@ -3283,7 +3290,7 @@ void mem_cgroup_end_migration(struct mem_cgroup *memcg,
> * and USED bit check in mem_cgroup_uncharge_page() will do enough
> * check. (see prepare_charge() also)
> */
> - if (PageAnon(used))
> + if (anon)
> mem_cgroup_uncharge_page(used);
> /*
> * At migration, we may charge account against cgroup which has no
> @@ -3313,7 +3320,7 @@ void mem_cgroup_replace_page_cache(struct page *oldpage,
> /* fix accounting on old pages */
> lock_page_cgroup(pc);
> memcg = pc->mem_cgroup;
> - mem_cgroup_charge_statistics(memcg, PageCgroupCache(pc), -1);
> + mem_cgroup_charge_statistics(memcg, false, -1);
> ClearPageCgroupUsed(pc);
> unlock_page_cgroup(pc);
>
> --
> 1.7.4.1
>
>
>
> --
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--
Michal Hocko
SUSE Labs
SUSE LINUX s.r.o.
Lihovarska 1060/12
190 00 Praha 9
Czech Republic


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