linux-ext4 - Re: [PATCHv5 2/9] fs/buffer.c: Add generic_buffer

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Date:   Mon, 17 Apr 2023 13:07:21 +0200
From:   Jan Kara <jack@...e.cz>
To:     "Ritesh Harjani (IBM)" <ritesh.list@...il.com>
Cc:     linux-fsdevel@...r.kernel.org, linux-ext4@...r.kernel.org,
        Jan Kara <jack@...e.cz>, Christoph Hellwig <hch@...radead.org>,
        "Darrick J . Wong" <djwong@...nel.org>,
        Ojaswin Mujoo <ojaswin@...ux.ibm.com>,
        Disha Goel <disgoel@...ux.ibm.com>,
        Christoph Hellwig <hch@....de>
Subject: Re: [PATCHv5 2/9] fs/buffer.c: Add generic_buffer_fsync
 implementation

On Mon 17-04-23 13:01:49, Jan Kara wrote:
> On Sun 16-04-23 15:38:37, Ritesh Harjani (IBM) wrote:
> > Some of the higher layers like iomap takes inode_lock() when calling
> > generic_write_sync().
> > Also writeback already happens from other paths without inode lock,
> > so it's difficult to say that we really need sync_mapping_buffers() to
> > take any inode locking here. Having said that, let's add
> > generic_buffer_fsync() implementation in buffer.c with no
> > inode_lock/unlock() for now so that filesystems like ext2 and
> > ext4's nojournal mode can use it.
> > 
> > Ext4 when got converted to iomap for direct-io already copied it's own
> > variant of __generic_file_fsync() without lock. Hence let's add a helper
> > API and use it both in ext2 and ext4.
> > 
> > Later we can review other filesystems as well to see if we can make
> > generic_buffer_fsync() which does not take any inode_lock() as the
> > default path.
> > 
> > Tested-by: Disha Goel <disgoel@...ux.ibm.com>
> > Reviewed-by: Christoph Hellwig <hch@....de>
> > Signed-off-by: Ritesh Harjani (IBM) <ritesh.list@...il.com>
> 
> There is a problem with generic_buffer_fsync() that it does not call
> blkdev_issue_flush() so the caller is responsible for doing that. That's
> necessary for ext2 & ext4 so fine for now.

Actually a slight correction: ext2 could use a variant of
generic_buffer_fsync() that flushes disk caches.

								Honza

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