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From: Brian Foster <bfoster@redhat.com>
To: Christoph Hellwig <hch@lst.de>
Cc: linux-xfs@vger.kernel.org, linux-fsdevel@vger.kernel.org,
	linux-mm@kvack.org, Dave Chinner <dchinner@redhat.com>
Subject: Re: [PATCH 22/34] xfs: make xfs_writepage_map extent map centric
Date: Fri, 25 May 2018 07:35:33 -0400	[thread overview]
Message-ID: <20180525113532.GA92036@bfoster.bfoster> (raw)
In-Reply-To: <20180525061900.GA16409@lst.de>

On Fri, May 25, 2018 at 08:19:00AM +0200, Christoph Hellwig wrote:
> On Thu, May 24, 2018 at 02:13:56PM -0400, Brian Foster wrote:
> > Ok, so I guess writeback can see uptodate blocks over a hole if some
> > other block in that page is dirty.
> 
> Yes.
> 
> > Perhaps we could make sure that a
> > dirty page has at least one block that maps to an actual extent or
> > otherwise the page has been truncated..?
> 
> We have the following comment near the end of xfs_writepage_map:
> 

That comment is what I'm basing on...

> 	/*
> 	 * We can end up here with no error and nothing to write if we
> 	 * race with a partial page truncate on a sub-page block sized
> 	 * filesystem. In that case we need to mark the page clean.
> 	 */
> 

So we can correctly end up with nothing to write on a dirty page, but it
presumes a race with truncate. So suppose we end up with a dirty page,
at least one uptodate block, count is zero (i.e., due to holes) and
i_size is beyond the page. Would that not be completely bogus? If bogus,
I think that would at least detect the dumb example I posted earlier.

Brian

> And I'm pretty sure I managed to hit that case easily in xfstests,
> as my initial handling of it was wrong.  So I don't think we can
> even check for that.
> 
> > I guess having another dirty block bitmap similar to
> > iomap_page->uptodate could be required to tell for sure whether a
> > particular block should definitely have a block on-disk or not. It may
> > not be worth doing that just for additional error checks, but I still
> > have to look into the last few patches to grok all the iomap_page stuff.
> 
> I don't think it's worth it.  The sub-page dirty tracking has been one
> of the issues with the buffer head code that caused a lot of problems,
> and that we want to get rid of.
> --
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  reply	other threads:[~2018-05-25 11:35 UTC|newest]

Thread overview: 75+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-05-23 14:43 buffered I/O without buffer heads in xfs and iomap v3 Christoph Hellwig
2018-05-23 14:43 ` [PATCH 01/34] block: add a lower-level bio_add_page interface Christoph Hellwig
2018-05-30  5:28   ` Darrick J. Wong
2018-05-23 14:43 ` [PATCH 02/34] fs: factor out a __generic_write_end helper Christoph Hellwig
2018-05-30  5:30   ` Darrick J. Wong
2018-05-23 14:43 ` [PATCH 03/34] fs: move page_cache_seek_hole_data to iomap.c Christoph Hellwig
2018-05-30  5:31   ` Darrick J. Wong
2018-05-23 14:43 ` [PATCH 04/34] fs: remove the buffer_unwritten check in page_seek_hole_data Christoph Hellwig
2018-05-30  5:36   ` Darrick J. Wong
2018-05-23 14:43 ` [PATCH 05/34] fs: use ->is_partially_uptodate in page_cache_seek_hole_data Christoph Hellwig
2018-05-30  5:41   ` Darrick J. Wong
2018-05-23 14:43 ` [PATCH 06/34] mm: give the 'ret' variable a better name __do_page_cache_readahead Christoph Hellwig
2018-05-30  5:42   ` Darrick J. Wong
2018-05-23 14:43 ` [PATCH 07/34] mm: return an unsigned int from __do_page_cache_readahead Christoph Hellwig
2018-05-30  5:44   ` Darrick J. Wong
2018-05-23 14:43 ` [PATCH 08/34] mm: split ->readpages calls to avoid non-contiguous pages lists Christoph Hellwig
2018-05-30  5:46   ` Darrick J. Wong
2018-05-23 14:43 ` [PATCH 09/34] iomap: inline data should be an iomap type, not a flag Christoph Hellwig
2018-05-30  5:49   ` Darrick J. Wong
2018-05-23 14:43 ` [PATCH 10/34] iomap: fix the comment describing IOMAP_NOWAIT Christoph Hellwig
2018-05-30  5:49   ` Darrick J. Wong
2018-05-23 14:43 ` [PATCH 11/34] iomap: move IOMAP_F_BOUNDARY to gfs2 Christoph Hellwig
2018-05-30  5:50   ` Darrick J. Wong
2018-05-30  9:30     ` [Cluster-devel] " Steven Whitehouse
2018-05-30  9:59       ` Christoph Hellwig
2018-05-30 10:02         ` Steven Whitehouse
2018-05-30 10:10           ` Christoph Hellwig
2018-05-30 10:12             ` Steven Whitehouse
2018-05-30 11:03               ` Andreas Gruenbacher
2018-05-23 14:43 ` [PATCH 12/34] iomap: use __bio_add_page in iomap_dio_zero Christoph Hellwig
2018-05-30  5:51   ` Darrick J. Wong
2018-05-23 14:43 ` [PATCH 13/34] iomap: add a iomap_sector helper Christoph Hellwig
2018-05-30  5:52   ` Darrick J. Wong
2018-05-23 14:43 ` [PATCH 14/34] iomap: add an iomap-based bmap implementation Christoph Hellwig
2018-05-30  5:54   ` Darrick J. Wong
2018-05-23 14:43 ` [PATCH 15/34] iomap: add an iomap-based readpage and readpages implementation Christoph Hellwig
2018-05-30  6:11   ` Darrick J. Wong
2018-05-30  6:23     ` Christoph Hellwig
2018-05-23 14:43 ` [PATCH 16/34] iomap: add initial support for writes without buffer heads Christoph Hellwig
2018-05-30  6:21   ` Darrick J. Wong
2018-05-23 14:43 ` [PATCH 17/34] xfs: use iomap_bmap Christoph Hellwig
2018-05-30  6:14   ` Darrick J. Wong
2018-05-23 14:43 ` [PATCH 18/34] xfs: use iomap for blocksize == PAGE_SIZE readpage and readpages Christoph Hellwig
2018-05-30  6:22   ` Darrick J. Wong
2018-05-23 14:43 ` [PATCH 19/34] xfs: simplify xfs_bmap_punch_delalloc_range Christoph Hellwig
2018-05-23 16:17   ` Brian Foster
2018-05-24  8:01     ` Christoph Hellwig
2018-05-23 14:43 ` [PATCH 20/34] xfs: simplify xfs_aops_discard_page Christoph Hellwig
2018-05-23 14:43 ` [PATCH 21/34] xfs: move locking into xfs_bmap_punch_delalloc_range Christoph Hellwig
2018-05-23 14:43 ` [PATCH 22/34] xfs: make xfs_writepage_map extent map centric Christoph Hellwig
2018-05-24 14:59   ` Brian Foster
2018-05-24 16:53     ` Christoph Hellwig
2018-05-24 18:13       ` Brian Foster
2018-05-25  6:19         ` Christoph Hellwig
2018-05-25 11:35           ` Brian Foster [this message]
2018-05-28  7:15             ` Christoph Hellwig
2018-05-29 11:26               ` Brian Foster
2018-05-29 13:08                 ` Christoph Hellwig
2018-05-29 17:04                   ` Brian Foster
2018-05-23 14:43 ` [PATCH 23/34] xfs: remove the now unused XFS_BMAPI_IGSTATE flag Christoph Hellwig
2018-05-23 14:43 ` [PATCH 24/34] xfs: remove xfs_reflink_find_cow_mapping Christoph Hellwig
2018-05-23 14:43 ` [PATCH 25/34] xfs: remove xfs_reflink_trim_irec_to_next_cow Christoph Hellwig
2018-05-24 14:59   ` Brian Foster
2018-05-24 15:06     ` Brian Foster
2018-05-24 17:10       ` Christoph Hellwig
2018-05-23 14:43 ` [PATCH 26/34] xfs: simplify xfs_map_blocks by using xfs_iext_lookup_extent directly Christoph Hellwig
2018-05-23 14:43 ` [PATCH 27/34] xfs: don't clear imap_valid for a non-uptodate buffers Christoph Hellwig
2018-05-23 14:43 ` [PATCH 28/34] xfs: remove the imap_valid flag Christoph Hellwig
2018-05-23 14:43 ` [PATCH 29/34] xfs: don't look at buffer heads in xfs_add_to_ioend Christoph Hellwig
2018-05-23 14:43 ` [PATCH 30/34] xfs: move all writeback buffer_head manipulation into xfs_map_at_offset Christoph Hellwig
2018-05-23 14:43 ` [PATCH 31/34] xfs: remove xfs_start_page_writeback Christoph Hellwig
2018-05-23 14:43 ` [PATCH 32/34] xfs: refactor the tail of xfs_writepage_map Christoph Hellwig
2018-05-23 14:43 ` [PATCH 33/34] xfs: do not set the page uptodate in xfs_writepage_map Christoph Hellwig
2018-05-23 14:43 ` [PATCH 34/34] xfs: allow writeback on pages without buffer heads Christoph Hellwig
  -- strict thread matches above, loose matches on Subject: below --
2018-05-18 16:47 buffered I/O without buffer heads in xfs and iomap v2 Christoph Hellwig
2018-05-18 16:48 ` [PATCH 22/34] xfs: make xfs_writepage_map extent map centric Christoph Hellwig

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