linux-kernel - Re: [PATCH] fix leak of swap accounting as stale swap cache under memcg

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Message-Id: <20090427210856.d5f4109e.d-nishimura@mtf.biglobe.ne.jp>
Date:	Mon, 27 Apr 2009 21:08:56 +0900
From:	Daisuke Nishimura <d-nishimura@....biglobe.ne.jp>
To:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Cc:	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	"balbir@...ux.vnet.ibm.com" <balbir@...ux.vnet.ibm.com>,
	"nishimura@....nes.nec.co.jp" <nishimura@....nes.nec.co.jp>,
	"hugh@...itas.com" <hugh@...itas.com>,
	"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] fix leak of swap accounting as stale swap cache under
 memcg

> Index: mmotm-2.6.30-Apr24/mm/vmscan.c
> ===================================================================
> --- mmotm-2.6.30-Apr24.orig/mm/vmscan.c
> +++ mmotm-2.6.30-Apr24/mm/vmscan.c
> @@ -661,6 +661,9 @@ static unsigned long shrink_page_list(st
>  		if (PageAnon(page) && !PageSwapCache(page)) {
>  			if (!(sc->gfp_mask & __GFP_IO))
>  				goto keep_locked;
> +			/* avoid making more stale swap caches */
> +			if (memcg_stale_swap_congestion())
> +				goto keep_locked;
>  			if (!add_to_swap(page))
>  				goto activate_locked;
>  			may_enter_fs = 1;
> 
Well, as I mentioned before(http://marc.info/?l=linux-kernel&m=124066623510867&w=2),
this cannot avoid type-2(set !PageCgroupUsed by the owner process via
page_remove_rmap()->mem_cgroup_uncharge_page() before being added to swap cache).
If these swap caches go through shrink_page_list() without beeing freed
for some reason, these swap caches doesn't go back to memcg's LRU.

Type-2 doesn't pressure memsw.usage, but you can see it by plotting
"grep SwapCached /proc/meminfo".

And I don't think it's a good idea to add memcg_stale_swap_congestion() here.
This means less possibility to reclaim pages.

Do you dislike the patch I attached in the above mail ?

If not, please merge it(I tested your prvious version with some fixes and
my patch, and it worked well). Or shall I send is as a separate patch
to fix type-2 after your patch(yours looks good to me for type-1)?
(to tell the truth, I want reuse memcg_free_unused_swapcache() in another patch)


Thanks,
Daisuke Nishimura.
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