linux-kernel - Re: [PATCH v7 15/19] iomap: Support partial direct I/O on user copy failures

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Message-ID: <CAHc6FU4_3m-f2T360Vq-WF=nkqDq9Zc+dekRt+wrcjvbUR1oSQ@mail.gmail.com>
Date:   Tue, 28 Sep 2021 17:05:46 +0200
From:   Andreas Gruenbacher <agruenba@...hat.com>
To:     Christoph Hellwig <hch@...radead.org>
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        "Darrick J. Wong" <djwong@...nel.org>, Jan Kara <jack@...e.cz>,
        Matthew Wilcox <willy@...radead.org>,
        cluster-devel <cluster-devel@...hat.com>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>, ocfs2-devel@....oracle.com
Subject: Re: [PATCH v7 15/19] iomap: Support partial direct I/O on user copy failures

On Thu, Sep 9, 2021 at 1:22 PM Christoph Hellwig <hch@...radead.org> wrote:
> On Fri, Aug 27, 2021 at 06:49:22PM +0200, Andreas Gruenbacher wrote:
> > In iomap_dio_rw, when iomap_apply returns an -EFAULT error and the
> > IOMAP_DIO_PARTIAL flag is set, complete the request synchronously and
> > return a partial result.  This allows the caller to deal with the page
> > fault and retry the remainder of the request.
> >
> > Signed-off-by: Andreas Gruenbacher <agruenba@...hat.com>
> > ---
> >  fs/iomap/direct-io.c  | 6 ++++++
> >  include/linux/iomap.h | 7 +++++++
> >  2 files changed, 13 insertions(+)
> >
> > diff --git a/fs/iomap/direct-io.c b/fs/iomap/direct-io.c
> > index 8054f5d6c273..ba88fe51b77a 100644
> > --- a/fs/iomap/direct-io.c
> > +++ b/fs/iomap/direct-io.c
> > @@ -561,6 +561,12 @@ __iomap_dio_rw(struct kiocb *iocb, struct iov_iter *iter,
> >               ret = iomap_apply(inode, pos, count, iomap_flags, ops, dio,
> >                               iomap_dio_actor);
> >               if (ret <= 0) {
> > +                     if (ret == -EFAULT && dio->size &&
> > +                         (dio_flags & IOMAP_DIO_PARTIAL)) {
> > +                             wait_for_completion = true;
> > +                             ret = 0;
>
> Do we need a NOWAIT check here to skip the wait_for_completion
> for that case?

Hmm, you're probably right, yes. I'll add that.

Thanks,
Andreas