linux-kernel - Re: Kernel falls apart under light memory pressure (i.e. linking vmlinux)

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: <20110517055204.GB24069@localhost>
Date:	Tue, 17 May 2011 13:52:04 +0800
From:	Wu Fengguang <fengguang.wu@...el.com>
To:	Minchan Kim <minchan.kim@...il.com>
Cc:	Andi Kleen <andi@...stfloor.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	Andrew Lutomirski <luto@....edu>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: Kernel falls apart under light memory pressure (i.e. linking
 vmlinux)

On Mon, May 16, 2011 at 07:40:42AM +0900, Minchan Kim wrote:
> On Mon, May 16, 2011 at 12:27 AM, Wu Fengguang <fengguang.wu@...el.com> wrote:
> > On Sun, May 15, 2011 at 09:37:58AM +0800, Minchan Kim wrote:
> >> On Sun, May 15, 2011 at 2:43 AM, Andi Kleen <andi@...stfloor.org> wrote:
> >> > Copying back linux-mm.
> >> >
> >> >> Recently, we added following patch.
> >> >> https://lkml.org/lkml/2011/4/26/129
> >> >> If it's a culprit, the patch should solve the problem.
> >> >
> >> > It would be probably better to not do the allocations at all under
> >> > memory pressure.  Even if the RA allocation doesn't go into reclaim
> >>
> >> Fair enough.
> >> I think we can do it easily now.
> >> If page_cache_alloc_readahead(ie, GFP_NORETRY) is fail, we can adjust
> >> RA window size or turn off a while. The point is that we can use the
> >> fail of __do_page_cache_readahead as sign of memory pressure.
> >> Wu, What do you think?
> >
> > No, disabling readahead can hardly help.
> 
> I don't mean we have to disable RA.
> As I said, the point is that we can use __GFP_NORETRY alloc fail as
> _sign_ of memory pressure.

I see.

> >
> > The sequential readahead memory consumption can be estimated by
> >
> >                2 * (number of concurrent read streams) * (readahead window size)
> >
> > And you can double that when there are two level of readaheads.
> >
> > Since there are hardly any concurrent read streams in Andy's case,
> > the readahead memory consumption will be ignorable.
> >
> > Typically readahead thrashing will happen long before excessive
> > GFP_NORETRY failures, so the reasonable solutions are to
> 
> If it is, RA thrashing could be better sign than failure of __GFP_NORETRY.
> If we can do it easily, I don't object it. :)

Yeah, the RA thrashing is much better sign because it not only happens
long before normal __GFP_NORETRY failures, but also offers hint on how
tight memory pressure it is. We can then shrink the readahead window
adaptively to the available page cache memory :)

> >
> > - shrink readahead window on readahead thrashing
> >  (current readahead heuristic can somehow do this, and I have patches
> >  to further improve it)
> 
> Good to hear. :)
> I don't want RA steals high order page in memory pressure.

More often than not it won't be RA's fault :)  When you see RA page
allocations stealing high order pages, it may actually be reflecting
some more general order-0 steal order-N problem..

> My patch and shrinking RA window helps this case.

Thanks,
Fengguang
--
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/