linux-kernel - Re: [PATCH 2.6.19-rc3] VFS: per-sb dentry lru list

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Message-ID: <454616BE.7040900@sw.ru>
Date:	Mon, 30 Oct 2006 18:14:06 +0300
From:	Kirill Korotaev <dev@...ru>
To:	Andrew Morton <akpm@...l.org>
CC:	Vasily Averin <vvs@...ru>, David Howells <dhowells@...hat.com>,
	Neil Brown <neilb@...e.de>, Jan Blunck <jblunck@...e.de>,
	Olaf Hering <olh@...e.de>, Balbir Singh <balbir@...ibm.com>,
	Kirill Korotaev <dev@...nvz.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	devel@...nvz.org
Subject: Re: [PATCH 2.6.19-rc3] VFS: per-sb dentry lru list

Andrew,

>>Virtuozzo/OpenVZ linux kernel team has discovered that umount/remount can last
>>for hours looping in shrink_dcache_sb() without much successes. Since during
>>shrinking s_umount semaphore is taken lots of other unrelated operations like
>>sync can stop working until shrink finished.
> 
> 
> Did you consider altering shrink_dcache_sb() so that it holds onto
> dcache_lock and moves all the to-be-pruned dentries onto a private list in
> a single pass, then prunes them all outside the lock?

moving dentries from global list to the local one can take arbitrary number
of milliseconds (with huge amount of memory), so nothing good here from latency
view point.

Thanks,
Kirill

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