From: Brian Foster <bfoster@redhat.com>
To: Christoph Hellwig <hch@infradead.org>
Cc: linux-fsdevel@vger.kernel.org, linux-xfs@vger.kernel.org
Subject: Re: [PATCH 2/2] iomap: zero cached pages over unwritten extents on zero range
Date: Mon, 19 Oct 2020 14:01:44 -0400 [thread overview]
Message-ID: <20201019180144.GC1232435@bfoster> (raw)
In-Reply-To: <20201019165519.GB1232435@bfoster>
On Mon, Oct 19, 2020 at 12:55:19PM -0400, Brian Foster wrote:
> On Thu, Oct 15, 2020 at 10:49:01AM +0100, Christoph Hellwig wrote:
> > > +iomap_zero_range_skip_uncached(struct inode *inode, loff_t *pos,
> > > + loff_t *count, loff_t *written)
> > > +{
> > > + unsigned dirty_offset, bytes = 0;
> > > +
> > > + dirty_offset = page_cache_seek_hole_data(inode, *pos, *count,
> > > + SEEK_DATA);
> > > + if (dirty_offset == -ENOENT)
> > > + bytes = *count;
> > > + else if (dirty_offset > *pos)
> > > + bytes = dirty_offset - *pos;
> > > +
> > > + if (bytes) {
> > > + *pos += bytes;
> > > + *count -= bytes;
> > > + *written += bytes;
> > > + }
> >
> > I find the calling conventions weird. why not return bytes and
> > keep the increments/decrements of the three variables in the caller?
> >
>
> No particular reason. IIRC I had it both ways and just landed on this.
> I'd change it, but as mentioned in the patch 1 thread I don't think this
> patch is sufficient (with or without patch 1) anyways because the page
> can also have been reclaimed before we get here.
>
Christoph,
What do you think about introducing behavior specific to
iomap_truncate_page() to unconditionally write zeroes over unwritten
extents? AFAICT that addresses the race and was historical XFS behavior
(via block_truncate_page()) before iomap, so is not without precedent.
What I'd probably do is bury the caller's did_zero parameter into a new
internal struct iomap_zero_data to pass down into
iomap_zero_range_actor(), then extend that structure with a
'zero_unwritten' field such that iomap_zero_range_actor() can do this:
if (srcmap->type == IOMAP_HOLE ||
(srcmap->type == IOMAP_UNWRITTEN && !zdata->zero_unwritten))
return count;
iomap_truncate_page() would set that flag either via open coding
iomap_zero_range() or creating a new internal wrapper. Hm?
Brian
> Brian
>
next prev parent reply other threads:[~2020-10-19 18:01 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-10-12 14:03 [PATCH 0/2] iomap: zero dirty pages over unwritten extents Brian Foster
2020-10-12 14:03 ` [PATCH 1/2] iomap: use page dirty state to seek data " Brian Foster
2020-10-13 12:30 ` Brian Foster
2020-10-13 22:53 ` Dave Chinner
2020-10-14 12:59 ` Brian Foster
2020-10-14 22:37 ` Dave Chinner
2020-10-15 9:47 ` Christoph Hellwig
2020-10-19 16:55 ` Brian Foster
2020-10-27 18:07 ` Christoph Hellwig
2020-10-28 11:31 ` Brian Foster
2020-10-12 14:03 ` [PATCH 2/2] iomap: zero cached pages over unwritten extents on zero range Brian Foster
2020-10-15 9:49 ` Christoph Hellwig
2020-10-19 16:55 ` Brian Foster
2020-10-19 18:01 ` Brian Foster [this message]
2020-10-20 16:21 ` Brian Foster
2020-10-27 18:15 ` Christoph Hellwig
2020-10-28 11:31 ` Brian Foster
2020-10-23 1:02 ` [iomap] 11b5156248: xfstests.xfs.310.fail kernel test robot
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