linux-kernel - Re: [dm-devel] [PATCH 0/6] dax poison recovery with RWF_RECOVERY

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Date:   Thu, 21 Oct 2021 22:38:00 -0700
From:   Christoph Hellwig <hch@...radead.org>
To:     "Darrick J. Wong" <djwong@...nel.org>
Cc:     Jane Chu <jane.chu@...cle.com>,
        Christoph Hellwig <hch@...radead.org>,
        "david@...morbit.com" <david@...morbit.com>,
        "dan.j.williams@...el.com" <dan.j.williams@...el.com>,
        "vishal.l.verma@...el.com" <vishal.l.verma@...el.com>,
        "dave.jiang@...el.com" <dave.jiang@...el.com>,
        "agk@...hat.com" <agk@...hat.com>,
        "snitzer@...hat.com" <snitzer@...hat.com>,
        "dm-devel@...hat.com" <dm-devel@...hat.com>,
        "ira.weiny@...el.com" <ira.weiny@...el.com>,
        "willy@...radead.org" <willy@...radead.org>,
        "vgoyal@...hat.com" <vgoyal@...hat.com>,
        "linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
        "nvdimm@...ts.linux.dev" <nvdimm@...ts.linux.dev>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-xfs@...r.kernel.org" <linux-xfs@...r.kernel.org>
Subject: Re: [dm-devel] [PATCH 0/6] dax poison recovery with
 RWF_RECOVERY_DATA flag

On Thu, Oct 21, 2021 at 06:58:17PM -0700, Darrick J. Wong wrote:
> On Fri, Oct 22, 2021 at 01:37:28AM +0000, Jane Chu wrote:
> > On 10/21/2021 4:31 AM, Christoph Hellwig wrote:
> > > Looking over the series I have serious doubts that overloading the
> > > slow path clear poison operation over the fast path read/write
> > > path is such a great idea.
> 
> Why would data recovery after a media error ever be considered a
> fast/hot path?

Not sure what you're replying to (the text is from me, the mail you are
repling to is fom Jane), but my point is that the read/write
got path should not be overloaded with data recovery.

> A normal read/write to a fsdax file would not pass the
> flag, which skips the poison checking with whatever MCE consequences
> that has, right?

Exactly!

> pwritev2(..., RWF_RECOVER_DATA) should be infrequent enough that
> carefully stepping around dax_direct_access only has to be faster than
> restoring from backup, I hope?

Yes.  And thus be kept as separate as possible.