linux-kernel - Re: [patch 1/6] fs: icache RCU free inodes

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Message-ID: <20101109171522.GA4522@infradead.org>
Date:	Tue, 9 Nov 2010 12:15:22 -0500
From:	Christoph Hellwig <hch@...radead.org>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Eric Dumazet <eric.dumazet@...il.com>,
	Nick Piggin <npiggin@...nel.dk>,
	Al Viro <viro@...iv.linux.org.uk>,
	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org
Subject: Re: [patch 1/6] fs: icache RCU free inodes

On Tue, Nov 09, 2010 at 09:08:17AM -0800, Linus Torvalds wrote:
> Again, this is only an issue for non-dentry lookup. For the dentry
> case, we know that if the dentry still exists, then the inode still
> exists. So we don't need to check a stable inode pointer if we just
> verify the stability of the dentry - and we'll have to do that anyway
> obviously.

If the dentry still exists we have a reference on the inode and never
call into the inode hash.

> In other words: let's bite off the complexity in small chunks. Let's
> keep the inode lock approach for now for the actual inode lists and
> hash lookups. I think they are almost entirely independent issues from
> the dentry path.

I'm defintively in favour of splitting things into small chunks.  I
don't particularly care how we do it.  inode_lock scaling seems the
most simple bit to me, and even that turned out to be a massive
amount of work to do properly.

Doing the dentry_lock splitup last starts to look more and more
interesting given how messy inode_lock is, though.
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