linux-kernel - Re: [PATCH -mm] memcg: fix handling of shmem migration(v2)

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Date:	Wed, 17 Sep 2008 15:51:12 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Daisuke Nishimura <nishimura@....nes.nec.co.jp>
Cc:	kamezawa.hiroyu@...fujitsu.com, nishimura@....nes.nec.co.jp,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	balbir@...ux.vnet.ibm.com, xemul@...nvz.org
Subject: Re: [PATCH -mm] memcg: fix handling of shmem migration(v2)

On Wed, 17 Sep 2008 16:55:44 +0900
Daisuke Nishimura <nishimura@....nes.nec.co.jp> wrote:

> 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 added MEM_CGROUP_CHARGE_TYPE_SHMEM for precharge
> at shmem's page migration.
> 
> 
> ChangeLog: v1->v2
> - instead of modifying migrate.c, modify memcontrol.c only.
> - add MEM_CGROUP_CHARGE_TYPE_SHMEM.
> 
> 
> Signed-off-by: Daisuke Nishimura <nishimura@....nes.nec.co.jp>
> ---
>  mm/memcontrol.c |   13 ++++++++++---
>  1 files changed, 10 insertions(+), 3 deletions(-)
> 
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index 2979d22..ef8812d 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -179,6 +179,7 @@ enum charge_type {
>  	MEM_CGROUP_CHARGE_TYPE_CACHE = 0,
>  	MEM_CGROUP_CHARGE_TYPE_MAPPED,
>  	MEM_CGROUP_CHARGE_TYPE_FORCE,	/* used by force_empty */
> +	MEM_CGROUP_CHARGE_TYPE_SHMEM,	/* used by page migration of shmem */
>  };
>  
>  /*
> @@ -579,8 +580,10 @@ static int mem_cgroup_charge_common(struct page *page, struct mm_struct *mm,
>  			pc->flags |= PAGE_CGROUP_FLAG_FILE;
>  		else
>  			pc->flags |= PAGE_CGROUP_FLAG_ACTIVE;
> -	} else
> +	} else if (ctype == MEM_CGROUP_CHARGE_TYPE_MAPPED)
>  		pc->flags = PAGE_CGROUP_FLAG_ACTIVE;
> +	else /* MEM_CGROUP_CHARGE_TYPE_SHMEM */
> +		pc->flags = PAGE_CGROUP_FLAG_CACHE | PAGE_CGROUP_FLAG_ACTIVE;
>  
>  	lock_page_cgroup(page);
>  	if (unlikely(page_get_page_cgroup(page))) {
> @@ -739,8 +742,12 @@ int mem_cgroup_prepare_migration(struct page *page, struct page *newpage)
>  	if (pc) {
>  		mem = pc->mem_cgroup;
>  		css_get(&mem->css);
> -		if (pc->flags & PAGE_CGROUP_FLAG_CACHE)
> -			ctype = MEM_CGROUP_CHARGE_TYPE_CACHE;
> +		if (pc->flags & PAGE_CGROUP_FLAG_CACHE) {
> +			if (page_is_file_cache(page))
> +				ctype = MEM_CGROUP_CHARGE_TYPE_CACHE;
> +			else
> +				ctype = MEM_CGROUP_CHARGE_TYPE_SHMEM;
> +		}
>  	}
>  	unlock_page_cgroup(page);
>  	if (mem) {

I queued this as a fix against
vmscan-split-lru-lists-into-anon-file-sets.patch.  Was that appropriate?

If the bug you're fixing here is also present in mainline then I'll
need to ask for a tested patch against mainline, please.



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