linux-kernel - Re: swapping when there's a free memory

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] [day] [month] [year] [list]

Message-ID: <alpine.DEB.1.10.1004300543290.13905@artax.karlin.mff.cuni.cz>
Date:	Fri, 30 Apr 2010 05:52:38 +0200 (CEST)
From:	Mikulas Patocka <mikulas@...ax.karlin.mff.cuni.cz>
To:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Pavel Machek <pavel@....cz>, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org
Subject: Re: swapping when there's a free memory



On Tue, 27 Apr 2010, KAMEZAWA Hiroyuki wrote:

> On Mon, 26 Apr 2010 15:33:33 -0700
> Andrew Morton <akpm@...ux-foundation.org> wrote:
> 
> > On Sun, 25 Apr 2010 09:13:49 +0200
> > Pavel Machek <pavel@....cz> wrote:
> > 
> > > Hi!
> > > 
> > > > I captured this output of vmstat. The machine was freeing cache and 
> > > > swapping out pages even when there was a plenty of free memory.
> > > > 
> > > > The machine is sparc64 with 1GB RAM with 2.6.34-rc4. This abnormal 
> > > > swapping happened during running spadfsck --- a fsck program for a custom 
> > > > filesystem that caches most reads in its internal cache --- so it reads 
> > > > buffers and allocates memory at the same time.
> > > > 
> > > > Note that sparc64 doesn't have any low/high memory zones, so it couldn't 
> > > > be explained by filling one zone and needing to allocate pages in it.
> > > 
> > > Fragmented memory + high-order allocation?
> > 
> > Yeah, could be.  I wonder which slab/slub/slob implementation you're
> > using, and what page sizes it uses for dentries, inodes, etc.  Can you
> > have a poke in /prob/slabinfo?

It uses one page-per-slab for dentries and two for inodes. But there was 
certainly no dentry or inode-based load --- the machine runs without X 
with minimum daemons, there is no major background work. There was just a 
process reading 128-kbyte blocks from a raw device and caching them in its 
userspace that triggered this. Can it be that kernel uses high-order 
allocations for reading from a buffer cache?

> And please /proc/buddyinfo and /proc/zoneinfo when the system is swappy.

It happens rarely, I don't know if I catch it at the right time. The 
report I sent, was what I found in a scrollback of vmstat. I didn't catch 
it in real time.

> Thanks,
> -Kame

Mikulas
--
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/