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

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Message-ID: <YXJN4s1HC/Y+KKg1@infradead.org>
Date:   Thu, 21 Oct 2021 22:36:34 -0700
From:   Christoph Hellwig <hch@...radead.org>
To:     Jane Chu <jane.chu@...cle.com>
Cc:     Christoph Hellwig <hch@...radead.org>,
        "david@...morbit.com" <david@...morbit.com>,
        "djwong@...nel.org" <djwong@...nel.org>,
        "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 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.
> > 
> 
> Understood, sounds like a concern on principle. But it seems to me
> that the task of recovery overlaps with the normal write operation
> on the write part. Without overloading some write operation for
> 'recovery', I guess we'll need to come up with a new userland
> command coupled with a new dax API ->clear_poison and propagate the
> new API support to each dm targets that support dax which, again,
> is an idea that sounds too bulky if I recall Dan's earlier rejection
> correctly.

When I wrote the above I mostly thought about the in-kernel API, that
is use a separate method.  But reading your mail and thinking about
this a bit more I'm actually less and less sure that overloading
pwritev2 and preadv2 with this at the syscall level makes sense either.
read/write are our I/O fast path.  We really should not overload the
core of the VFS with error recovery for a broken hardware interface.