linux-kernel - Re: [RFC PATCH] shrink_dcache

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Date:	Mon, 9 Jan 2012 14:04:50 -0500
From:	Christoph Hellwig <hch@...radead.org>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Al Viro <viro@...iv.linux.org.uk>,
	Christoph Hellwig <hch@...radead.org>,
	Miklos Szeredi <miklos@...redi.hu>,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
	mgorman@...e.de, gregkh@...e.de, akpm@...ux-foundation.org,
	david@...morbit.com
Subject: Re: [RFC PATCH] shrink_dcache_parent() deadlock

On Mon, Jan 09, 2012 at 10:46:22AM -0800, Linus Torvalds wrote:
> On Mon, Jan 9, 2012 at 10:30 AM, Linus Torvalds
> <torvalds@...ux-foundation.org> wrote:
> >
> > Here's a TOTALLY UNTESTED rebase of just that single patch from Dave.
> 
> Well, it boots, and the dentry cache shrinks under memory pressure. So
> it's not _totally_ untested now.
> 
> But I don't really see why it would fix Miklos' case. I think
> select_parent() may still end up touching the d_lru list of something
> that is on the 'dispose' list. So the patch looks like a nice cleanup,
> but it seems to be independent of the issue Miklos found.
> 
> What am I missing now?

After Dave's patch select_parent isolates dentries that are going to
be dropped directly to an on-stack list instead of abusing the LRU.

With that scheme the trylock and retry loop in __shrink_dcache_sb
goes away completely for this caller.
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