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Date:   Wed, 20 Jan 2021 17:56:24 +0000
From:   Matthew Wilcox <willy@infradead.org>
To:     Christoph Hellwig <hch@infradead.org>
Cc:     Jan Kara <jack@suse.cz>, linux-fsdevel@vger.kernel.org,
        linux-ext4@vger.kernel.org
Subject: Re: [PATCH 2/3] mm: Provide address_space operation for filling
 pages for read
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References: <20210120160611.26853-1-jack@suse.cz>
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 <20210120172836.GA3809508@infradead.org>
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On Wed, Jan 20, 2021 at 05:28:36PM +0000, Christoph Hellwig wrote:
> On Wed, Jan 20, 2021 at 06:27:05PM +0100, Jan Kara wrote:
> > This would mean pulling i_mmap_sem out from ext4/XFS/F2FS private inode
> > into the VFS inode. Which is fine by me but it would grow struct inode for
> > proc / tmpfs / btrfs (although for btrfs I'm not convinced it isn't
> > actually prone to the race and doesn't need similar protection as xfs /
> > ext4) so some people may object.
> 
> The btrfs folks are already looking into lifting it to common code.
> 
> Also I have a patch pending to remove a list_head from the inode to
> counter the size increase :)

We can get rid of nrexceptional as well:

https://lore.kernel.org/linux-fsdevel/20201026151849.24232-1-willy@infradead.org/

We can also reduce the size of the rwsem by one word by replacing the list_head with a single pointer.

https://git.infradead.org/users/willy/pagecache.git/shortlog/refs/heads/wlist

(haven't touched it in almost four years, seemed to have a bug last time
i looked at it).