linux-kernel - Re: [patch 00/12] mm: page_alloc: improve OOM mechanism and policy

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20150413124924.GB21790@dhcp22.suse.cz>
Date:	Mon, 13 Apr 2015 14:49:24 +0200
From:	Michal Hocko <mhocko@...e.cz>
To:	Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
Cc:	hannes@...xchg.org, david@...morbit.com, linux-mm@...ck.org,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
	torvalds@...ux-foundation.org, akpm@...ux-foundation.org,
	ying.huang@...el.com, aarcange@...hat.com, tytso@....edu
Subject: Re: [patch 00/12] mm: page_alloc: improve OOM mechanism and policy

On Sat 11-04-15 16:29:26, Tetsuo Handa wrote:
> Johannes Weiner wrote:
> > The argument here was always that NOFS allocations are very limited in
> > their reclaim powers and will trigger OOM prematurely.  However, the
> > way we limit dirty memory these days forces most cache to be clean at
> > all times, and direct reclaim in general hasn't been allowed to issue
> > page writeback for quite some time.  So these days, NOFS reclaim isn't
> > really weaker than regular direct reclaim.  The only exception is that
> > it might block writeback, so we'd go OOM if the only reclaimables left
> > were dirty pages against that filesystem.  That should be acceptable.
> > 
> > diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> > index 47981c5e54c3..fe3cb2b0b85b 100644
> > --- a/mm/page_alloc.c
> > +++ b/mm/page_alloc.c
> > @@ -2367,16 +2367,6 @@ __alloc_pages_may_oom(gfp_t gfp_mask, unsigned int order, int alloc_flags,
> >  		/* The OOM killer does not needlessly kill tasks for lowmem */
> >  		if (ac->high_zoneidx < ZONE_NORMAL)
> >  			goto out;
> > -		/* The OOM killer does not compensate for IO-less reclaim */
> > -		if (!(gfp_mask & __GFP_FS)) {
> > -			/*
> > -			 * XXX: Page reclaim didn't yield anything,
> > -			 * and the OOM killer can't be invoked, but
> > -			 * keep looping as per tradition.
> > -			 */
> > -			*did_some_progress = 1;
> > -			goto out;
> > -		}
> >  		if (pm_suspended_storage())
> >  			goto out;
> >  		/* The OOM killer may not free memory on a specific node */
> > 
> 
> I think this change will allow calling out_of_memory() which results in
> "oom_kill_process() is trivially called via pagefault_out_of_memory()"
> problem described in https://lkml.org/lkml/2015/3/18/219 .
> 
> I myself think that we should trigger OOM killer for !__GFP_FS allocation
> in order to make forward progress in case the OOM victim is blocked.
> So, my question about this change is whether we can accept involving OOM
> killer from page fault, no matter how trivially OOM killer will kill some
> process?

We trigger OOM killer from the page fault path for ages. In fact the memcg
will trigger memcg OOM killer _only_ from the page fault path because
this context is safe as we do not sit on any locks at the time.
-- 
Michal Hocko
SUSE Labs
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/