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

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Date:	Wed, 17 Sep 2008 22:43:58 -0700
From:	Balbir Singh <balbir@...ux.vnet.ibm.com>
To:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
CC:	Andrew Morton <akpm@...ux-foundation.org>,
	Daisuke Nishimura <nishimura@....nes.nec.co.jp>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org, xemul@...nvz.org
Subject: Re: [PATCH -mm] memcg: fix handling of shmem migration(v2)

KAMEZAWA Hiroyuki wrote:
> On Wed, 17 Sep 2008 15:51:12 -0700
> Andrew Morton <akpm@...ux-foundation.org> wrote:
> 
>> 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.
>>
> I think this bug depends on split-lru patch set.
> Mayne not in mainline yet...?

Yes, that sounds correct to me, this should be a -mm only patch.

-- 
	Balbir
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