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

[nishimura@mxp.nes.nec.co.jp]

> On Mon, 27 Apr 2009 21:08:56 +0900
> Daisuke Nishimura <d-nishimura@mtf.biglobe.ne.jp> wrote:
> 
>> > 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.
>> 
> Hmm. maybe adding congestion_wait() ?
> 
I don't think no hook before add_to_swap() is needed.

>> Do you dislike the patch I attached in the above mail ?
>> 
> I doubt whether the patch covers all type-2 case.
> 
hmm, I didn't see any leak anymore when I tested the patch.

But because of machine time limit, I could only test for about 3 hours.
(I had seen some leak at that point before applying my patch)
I'll test for longer time if possible.

>> 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)
>> 
>> 
> I'll consider again and post v3.
> But I'll go into a series of holidays, so, may not come back until May/6.
> 
It's the same for me :)


Thanks,
Daisuke Nishimura.

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