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Date:   Wed, 20 Jan 2021 18:27:05 +0100
From:   Jan Kara <jack@suse.cz>
To:     Christoph Hellwig <hch@infradead.org>
Cc:     Jan Kara <jack@suse.cz>, linux-fsdevel@vger.kernel.org,
        Matthew Wilcox <willy@infradead.org>,
        linux-ext4@vger.kernel.org
Subject: Re: [PATCH 2/3] mm: Provide address_space operation for filling
 pages for read
Message-ID: <20210120172705.GC24063@quack2.suse.cz>
References: <20210120160611.26853-1-jack@suse.cz>
 <20210120160611.26853-3-jack@suse.cz>
 <20210120162001.GB3790454@infradead.org>
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On Wed 20-01-21 16:20:01, Christoph Hellwig wrote:
> On Wed, Jan 20, 2021 at 05:06:10PM +0100, Jan Kara wrote:
> > Provide an address_space operation for filling pages needed for read
> > into page cache. Filesystems can use this operation to seriealize
> > page cache filling with e.g. hole punching properly.
> 
> Besides the impending rewrite of the area - having another indirection
> here is just horrible for performance.  If we want locking in this area
> it should be in core code and common for multiple file systems.

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.

								Honza
-- 
Jan Kara <jack@suse.com>
SUSE Labs, CR