linux-ext4 - Re: [PATCH 17/29] fsdax: factor out a dax

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Message-ID: <20211123224457.GL266024@magnolia>
Date:   Tue, 23 Nov 2021 14:44:57 -0800
From:   "Darrick J. Wong" <djwong@...nel.org>
To:     Dan Williams <dan.j.williams@...el.com>
Cc:     Christoph Hellwig <hch@....de>, Mike Snitzer <snitzer@...hat.com>,
        Ira Weiny <ira.weiny@...el.com>,
        device-mapper development <dm-devel@...hat.com>,
        linux-xfs <linux-xfs@...r.kernel.org>,
        Linux NVDIMM <nvdimm@...ts.linux.dev>,
        linux-s390 <linux-s390@...r.kernel.org>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        linux-erofs@...ts.ozlabs.org,
        linux-ext4 <linux-ext4@...r.kernel.org>,
        virtualization@...ts.linux-foundation.org
Subject: Re: [PATCH 17/29] fsdax: factor out a dax_memzero helper

On Tue, Nov 23, 2021 at 01:22:13PM -0800, Dan Williams wrote:
> On Tue, Nov 9, 2021 at 12:34 AM Christoph Hellwig <hch@....de> wrote:
> >
> > Factor out a helper for the "manual" zeroing of a DAX range to clean
> > up dax_iomap_zero a lot.
> >
> 
> Small / optional fixup below:
> 
> Reviewed-by: Dan Williams <dan.j.williams@...el.com>
> 
> > Signed-off-by: Christoph Hellwig <hch@....de>
> > ---
> >  fs/dax.c | 36 +++++++++++++++++++-----------------
> >  1 file changed, 19 insertions(+), 17 deletions(-)
> >
> > diff --git a/fs/dax.c b/fs/dax.c
> > index d7a923d152240..dc9ebeff850ab 100644
> > --- a/fs/dax.c
> > +++ b/fs/dax.c
> > @@ -1121,34 +1121,36 @@ static vm_fault_t dax_pmd_load_hole(struct xa_state *xas, struct vm_fault *vmf,
> >  }
> >  #endif /* CONFIG_FS_DAX_PMD */
> >
> > +static int dax_memzero(struct dax_device *dax_dev, pgoff_t pgoff,
> > +               unsigned int offset, size_t size)
> > +{
> > +       void *kaddr;
> > +       long rc;
> > +
> > +       rc = dax_direct_access(dax_dev, pgoff, 1, &kaddr, NULL);
> > +       if (rc >= 0) {
> 
> Technically this should be "> 0" because dax_direct_access() returns
> nr_available_pages @pgoff, but this isn't broken because
> dax_direct_access() converts the "zero pages available" case into
> -ERANGE.

Agreed.  With that fixed,
Reviewed-by: Darrick J. Wong <djwong@...nel.org>

--D

> 
> > +               memset(kaddr + offset, 0, size);
> > +               dax_flush(dax_dev, kaddr + offset, size);
> > +       }
> > +       return rc;
> > +}
> > +
> >  s64 dax_iomap_zero(loff_t pos, u64 length, struct iomap *iomap)
> >  {
> >         pgoff_t pgoff = dax_iomap_pgoff(iomap, pos);
> >         long rc, id;
> > -       void *kaddr;
> > -       bool page_aligned = false;
> >         unsigned offset = offset_in_page(pos);
> >         unsigned size = min_t(u64, PAGE_SIZE - offset, length);
> >
> > -       if (IS_ALIGNED(pos, PAGE_SIZE) && size == PAGE_SIZE)
> > -               page_aligned = true;
> > -
> >         id = dax_read_lock();
> > -
> > -       if (page_aligned)
> > +       if (IS_ALIGNED(pos, PAGE_SIZE) && size == PAGE_SIZE)
> >                 rc = dax_zero_page_range(iomap->dax_dev, pgoff, 1);
> >         else
> > -               rc = dax_direct_access(iomap->dax_dev, pgoff, 1, &kaddr, NULL);
> > -       if (rc < 0) {
> > -               dax_read_unlock(id);
> > -               return rc;
> > -       }
> > -
> > -       if (!page_aligned) {
> > -               memset(kaddr + offset, 0, size);
> > -               dax_flush(iomap->dax_dev, kaddr + offset, size);
> > -       }
> > +               rc = dax_memzero(iomap->dax_dev, pgoff, offset, size);
> >         dax_read_unlock(id);
> > +
> > +       if (rc < 0)
> > +               return rc;
> >         return size;
> >  }
> >
> > --
> > 2.30.2
> >