Re: [PATCH v5] memcg: remove PCG_CACHE page_cgroup flag

[Michal Hocko]

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@xxxxxxxxxxxxxx>

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

Acked-by: Michal Hocko <mhocko@xxxxxxx>

> ---
>  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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