linux-kernel - Re: [PATCH] remove throttle_vm

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: <20071007235433.GW995458@sgi.com>
Date:	Mon, 8 Oct 2007 09:54:33 +1000
From:	David Chinner <dgc@....com>
To:	Fengguang Wu <wfg@...l.ustc.edu.cn>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Miklos Szeredi <miklos@...redi.hu>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] remove throttle_vm_writeout()

On Fri, Oct 05, 2007 at 08:30:28PM +0800, Fengguang Wu wrote:
> The improvement could be:
> - kswapd is now explicitly preferred to do the writeout;

Careful. kswapd is much less efficient at writeout than pdflush
because it does not do low->high offset writeback per address space.
It just flushes the pages in LRU order and that turns writeback into
a non-sequential mess. I/O sizes decrease substantially and
throughput falls through the floor.

So if you want kswapd to take over all the writeback, it needs to do
writeback in the same manner as the background flushes. i.e.  by
grabbing page->mapping and flushing that in sequential order rather
than just the page on the end of the LRU....

I documented the effect of kswapd taking over writeback in this
paper (section 5.3):

http://oss.sgi.com/projects/xfs/papers/ols2006/ols-2006-paper.pdf

Cheers,

Dave.
-- 
Dave Chinner
Principal Engineer
SGI Australian Software Group
-
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/