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

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Date:	Wed, 20 Oct 2010 14:07:04 +1100
From:	Nick Piggin <npiggin@...nel.dk>
To:	Christoph Hellwig <hch@...radead.org>
Cc:	npiggin@...nel.dk, 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 12:33:27PM -0400, Christoph Hellwig wrote:
> 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.

Probably bad wording of "anon". It should be "raw", maybe. The
filesystem is then of course responsible for adding i_ino and/or
to lists.


> 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.

I'll check it.

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