linux-kernel - Re: [PATCH v2 09/10] fs/xfs: Handle CoW for fsdax write() path

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Message-ID: <20210303104336.GA20371@lst.de>
Date:   Wed, 3 Mar 2021 11:43:36 +0100
From:   Christoph Hellwig <hch@....de>
To:     "ruansy.fnst@...itsu.com" <ruansy.fnst@...itsu.com>
Cc:     Christoph Hellwig <hch@....de>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-xfs@...r.kernel.org" <linux-xfs@...r.kernel.org>,
        "linux-nvdimm@...ts.01.org" <linux-nvdimm@...ts.01.org>,
        "linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
        "darrick.wong@...cle.com" <darrick.wong@...cle.com>,
        "dan.j.williams@...el.com" <dan.j.williams@...el.com>,
        "willy@...radead.org" <willy@...radead.org>,
        "jack@...e.cz" <jack@...e.cz>,
        "viro@...iv.linux.org.uk" <viro@...iv.linux.org.uk>,
        "linux-btrfs@...r.kernel.org" <linux-btrfs@...r.kernel.org>,
        "ocfs2-devel@....oracle.com" <ocfs2-devel@....oracle.com>,
        "david@...morbit.com" <david@...morbit.com>,
        "rgoldwyn@...e.de" <rgoldwyn@...e.de>
Subject: Re: [PATCH v2 09/10] fs/xfs: Handle CoW for fsdax write() path

On Wed, Mar 03, 2021 at 09:57:48AM +0000, ruansy.fnst@...itsu.com wrote:
> > What is the advantage of the ioemap_end handler here?  It adds another
> > indirect funtion call to the fast path, so if we can avoid it, I'd
> > rather do that.
> 
> These code were in xfs_file_dax_write().  I moved them into the iomap_end
> because the mmaped CoW need this.
> 
> I know this is not so good, but I could not find another better way. Do you
> have any ideas? 

mmaped copy is the copy_edge case?  Maybe just use different iomap_ops for
that case vs plain write?