linux-kernel - Re: [patch 26/35] fs: icache alloc anonymous inode allocation

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Message-ID: <20101019163327.GA5987@infradead.org>
Date:	Tue, 19 Oct 2010 12:33:27 -0400
From:	Christoph Hellwig <hch@...radead.org>
To:	npiggin@...nel.dk
Cc:	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org
Subject: Re: [patch 26/35] fs: icache alloc anonymous inode allocation

On Tue, Oct 19, 2010 at 02:42:42PM +1100, npiggin@...nel.dk wrote:
> Provide new_anon_inode function for inodes without a default inode number, and
> not on sb list. This can enable filesystems to reduce locking. "Real"
> filesystems can also reduce locking by allocating anonymous inode first, then
> adding it to lists after finding the inode number.

Having an _anon inode allocation for fileystsem that do manage the inode
lifetime is fine, but please don't mix that up with i_ino assignment,
as they are two totally different things.

Disk and network filesystem do not need a default i_ino, but they
absolutely do no need their inodes to be on the per-sb list.
anonfs/pipe/socket (and nothing else) can do away with the per-sb list,
but they do need a pseudo inode number.

I have a version of this port to Dave's tree which gets this right.
i_ino assignment is already moved out by my patch (which should apply
to your tree with minimal differences), so the new _anon only does not
put the inode on the list.  The other difference is that we don't bother
initializing i_sb_list in the main inode allocation path, but only in
new_anon_inode, and that the function is not exported - it really should
only be used for built-in filesystems that never get unmounted to be
safe.

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