linux-kernel - Re: [PATCH] mm: make VM_MAX

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]

Date:	Mon, 12 Oct 2009 17:39:21 +0800
From:	Wu Fengguang <fengguang.wu@...el.com>
To:	Christian Ehrhardt <ehrhardt@...ux.vnet.ibm.com>
Cc:	Martin Schwidefsky <schwidefsky@...ibm.com>,
	Jens Axboe <jens.axboe@...cle.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH] mm: make VM_MAX_READAHEAD configurable

On Mon, Oct 12, 2009 at 05:29:48PM +0800, Christian Ehrhardt wrote:
> Wu Fengguang wrote:
> > [SNIP]
> >>> May I ask for more details about your performance regression and why
> >>> it is related to readahead size? (we didn't change VM_MAX_READAHEAD..)
> >>>   
> >>>       
> >> Sure, the performance regression appeared when comparing Novell SLES10 
> >> vs. SLES11.
> >> While you are right Wu that the upstream default never changed so far, 
> >> SLES10 had a
> >> patch applied that set 512.
> >>     
> >
> > I see. I'm curious why SLES11 removed that patch. Did it experienced
> > some regressions with the larger readahead size?
> >
> >   
> 
> Only the obvious expected one with very low free/cacheable
> memory and a lot of parallel processes that do sequential I/O.
> The RA size scales up for all of them but 64xMaxRA then
> doesn't fit.
> 
> For example iozone with 64 threads (each on one disk for its own),
> sequential access pattern read with I guess 10 M free for cache
> suffered by ~15% due to trashing.

FYI, I just finished with a patch for dealing with readahead
thrashing.  Will do some tests and post the result :)

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/