linux-kernel - Re: [PATCH 02/17] fs: icache lock s

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Message-ID: <20101016075411.GA19147@amd>
Date:	Sat, 16 Oct 2010 18:54:11 +1100
From:	Nick Piggin <npiggin@...nel.dk>
To:	Christoph Hellwig <hch@...radead.org>
Cc:	Dave Chinner <david@...morbit.com>, linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 02/17] fs: icache lock s_inodes list

On Fri, Oct 01, 2010 at 01:49:09AM -0400, Christoph Hellwig wrote:
> On Wed, Sep 29, 2010 at 10:18:34PM +1000, Dave Chinner wrote:
> > From: Nick Piggin <npiggin@...e.de>
> > 
> > To allow removal of the inode_lock, we first need to protect the
> > superblock inode list with it's own lock instead of using the
> > inode_lock for this purpose. Nest the new sb_inode_list_lock inside
> > the inode_lock around the list operations it needs to protect.
> 
> Is there any good reason not to make this lock per-superblock?

Because in the first part of the inode lock series, it is breaking
locks in obvious small steps as possible, by adding global locks
protecting bits of what inode_lock used to.

If we did want to make it per-superblock, that would come at the
last part of the series, where inode_lock is removed and steps are
being taken to improve scalability and locking.

But I don't see why we want to make it per-superblock really anyway.
We want to have scalability within a single superblock, so per CPU
locks are needed. Once we have those, per-superblock doesn't really
buy much.

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