linux-kernel - Re: [PATCH 19/18] fs: split __inode_add_to

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Message-ID: <20101012104727.GC32255@dastard>
Date:	Tue, 12 Oct 2010 21:47:27 +1100
From:	Dave Chinner <david@...morbit.com>
To:	Christoph Hellwig <hch@...radead.org>
Cc:	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 19/18] fs: split __inode_add_to_list

On Sat, Oct 09, 2010 at 04:08:54AM -0400, Christoph Hellwig wrote:
> __inode_add_to_list does two things that aren't related.  First it adds
> the inode to the s_inodes list in the superblock, and second it optionally
> adds the inode to the inode hash.  Now that these don't even share the
> same lock there is no need to keeps this functionally together.  Split
> out an add_to_inode_hash helper from __insert_inode_hash to add an inode
> to a pre-calculated hash bucket for use by the various iget version, and
> a inode_add_to_sb_list helper from __inode_add_to_list to just add an
> inode to the per-sb list.  The inode.c-internal callers of
> __inode_add_to_list are converted to a sequence of inode_add_to_sb_list
> and __insert_inode_hash (if needed), and the only use of inode_add_to_list
> in XFS is replaced with a call to inode_add_to_sb_list and insert_inode_hash.

The only reason XFS hashed the inodes was to avoid problems in the
generic code that checked for unhashed inodes during clear_inode(). The
evict() changeover moved that unhashed check into
generic_drop_inode(), which the filesystem can override. Hence if
you add a ->drop_inode() method for XFS that just checks the link
count, we can avoid haѕhing the inodes altogether for XFS.

I can add another patch on top of this one to do that if you want...

Cheers,

Dave.
-- 
Dave Chinner
david@...morbit.com
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