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From: Qu Wenruo <quwenruo.btrfs@gmx.com>
To: Josef Bacik <josef@toxicpanda.com>, Qu Wenruo <wqu@suse.com>,
	linux-btrfs@vger.kernel.org
Subject: Re: [PATCH v4 01/18] btrfs: update locked page dirty/writeback/error bits in __process_pages_contig()
Date: Thu, 21 Jan 2021 14:32:42 +0800	[thread overview]
Message-ID: <c4bd841c-6657-5a72-85ac-fc8359c87a74@gmx.com> (raw)
In-Reply-To: <b0360753-072a-f5c5-3ea6-08e9db2445dd@toxicpanda.com>



On 2021/1/20 上午5:41, Josef Bacik wrote:
> On 1/16/21 2:15 AM, Qu Wenruo wrote:
>> When __process_pages_contig() get called for
>> extent_clear_unlock_delalloc(), if we hit the locked page, only Private2
>> bit is updated, but dirty/writeback/error bits are all skipped.
>>
>> There are several call sites call extent_clear_unlock_delalloc() with
>> @locked_page and PAGE_CLEAR_DIRTY/PAGE_SET_WRITEBACK/PAGE_END_WRITEBACK
>>
>> - cow_file_range()
>> - run_delalloc_nocow()
>> - cow_file_range_async()
>>    All for their error handling branches.
>>
>> For those call sites, since we skip the locked page for
>> dirty/error/writeback bit update, the locked page will still have its
>> dirty bit remaining.
>>
>> Thankfully, since all those call sites can only be hit with various
>> serious errors, it's pretty hard to hit and shouldn't affect regular
>> btrfs operations.
>>
>> But still, we shouldn't leave the locked_page with its
>> dirty/error/writeback bits untouched.
>>
>> Fix this by only skipping lock/unlock page operations for locked_page.
>>
>> Signed-off-by: Qu Wenruo <wqu@suse.com>
>
> Except this is handled by the callers.  We clear_page_dirty_for_io() the
> page before calling btrfs_run_delalloc_range(), so we don't need the
> PAGE_CLEAR_DIRTY, it's already cleared.  The SetPageError() is handled
> in the error path for locked_page, as is the
> set_writeback/end_writeback.  Now I don't think this patch causes
> problems specifically, but the changelog is at least wrong, and I'd
> rather we'd skip the handling of the locked_page here and leave it in
> the proper error handling.  If you need to do this for some other reason
> that I haven't gotten to yet then you need to make that clear in the
> changelog, because as of right now I don't see why this is needed.  Thanks,

This is mostly to co-operate with a later patch on
__process_pages_contig(), where we need to make sure page locked by
__process_pages_contig() is only unlocked by __process_pages_contig() too.

The exception is after cow_file_inline(), we call
__process_pages_contig() on the locked page, making it to clear page
writeback and unlock it.

That is going to cause problems for subpage.

Thus I prefer to make __process_pages_contig() to clear page dirty/end
writeback for locked page.

Thanks,
Qu
>
> Josef

  reply	other threads:[~2021-01-21  6:36 UTC|newest]

Thread overview: 68+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-01-16  7:15 [PATCH v4 00/18] btrfs: add read-only support for subpage sector size Qu Wenruo
2021-01-16  7:15 ` [PATCH v4 01/18] btrfs: update locked page dirty/writeback/error bits in __process_pages_contig() Qu Wenruo
2021-01-19 21:41   ` Josef Bacik
2021-01-21  6:32     ` Qu Wenruo [this message]
2021-01-21  6:51       ` Qu Wenruo
2021-01-23 19:13         ` David Sterba
2021-01-24  0:35           ` Qu Wenruo
2021-01-24 11:49             ` David Sterba
2021-01-16  7:15 ` [PATCH v4 02/18] btrfs: merge PAGE_CLEAR_DIRTY and PAGE_SET_WRITEBACK into PAGE_START_WRITEBACK Qu Wenruo
2021-01-19 21:43   ` Josef Bacik
2021-01-19 21:45   ` Josef Bacik
2021-01-16  7:15 ` [PATCH v4 03/18] btrfs: introduce the skeleton of btrfs_subpage structure Qu Wenruo
2021-01-18 22:46   ` David Sterba
2021-01-18 22:54     ` Qu Wenruo
2021-01-19 15:51       ` David Sterba
2021-01-19 16:06         ` David Sterba
2021-01-20  0:19           ` Qu Wenruo
2021-01-23 19:37             ` David Sterba
2021-01-24  0:24               ` Qu Wenruo
2021-01-18 23:01   ` David Sterba
2021-01-16  7:15 ` [PATCH v4 04/18] btrfs: make attach_extent_buffer_page() to handle subpage case Qu Wenruo
2021-01-18 22:51   ` David Sterba
2021-01-19 21:54   ` Josef Bacik
2021-01-19 22:35     ` David Sterba
2021-01-26  7:29       ` Qu Wenruo
2021-01-27 19:58         ` David Sterba
2021-01-20  0:27     ` Qu Wenruo
2021-01-20 14:22       ` Josef Bacik
2021-01-21  1:20         ` Qu Wenruo
2021-01-16  7:15 ` [PATCH v4 05/18] btrfs: make grab_extent_buffer_from_page() " Qu Wenruo
2021-01-16  7:15 ` [PATCH v4 06/18] btrfs: support subpage for extent buffer page release Qu Wenruo
2021-01-20 14:44   ` Josef Bacik
2021-01-21  0:45     ` Qu Wenruo
2021-01-16  7:15 ` [PATCH v4 07/18] btrfs: attach private to dummy extent buffer pages Qu Wenruo
2021-01-20 14:48   ` Josef Bacik
2021-01-21  0:47     ` Qu Wenruo
2021-01-16  7:15 ` [PATCH v4 08/18] btrfs: introduce helper for subpage uptodate status Qu Wenruo
2021-01-19 19:45   ` David Sterba
2021-01-20 14:55   ` Josef Bacik
2021-01-26  7:21     ` Qu Wenruo
2021-01-20 15:00   ` Josef Bacik
2021-01-21  0:49     ` Qu Wenruo
2021-01-21  1:28       ` Josef Bacik
2021-01-21  1:38         ` Qu Wenruo
2021-01-16  7:15 ` [PATCH v4 09/18] btrfs: introduce helper for subpage error status Qu Wenruo
2021-01-16  7:15 ` [PATCH v4 10/18] btrfs: make set/clear_extent_buffer_uptodate() to support subpage size Qu Wenruo
2021-01-16  7:15 ` [PATCH v4 11/18] btrfs: make btrfs_clone_extent_buffer() to be subpage compatible Qu Wenruo
2021-01-16  7:15 ` [PATCH v4 12/18] btrfs: implement try_release_extent_buffer() for subpage metadata support Qu Wenruo
2021-01-20 15:05   ` Josef Bacik
2021-01-21  0:51     ` Qu Wenruo
2021-01-23 20:36     ` David Sterba
2021-01-25 20:02       ` Josef Bacik
2021-01-16  7:15 ` [PATCH v4 13/18] btrfs: introduce read_extent_buffer_subpage() Qu Wenruo
2021-01-20 15:08   ` Josef Bacik
2021-01-16  7:15 ` [PATCH v4 14/18] btrfs: extent_io: make endio_readpage_update_page_status() to handle subpage case Qu Wenruo
2021-01-16  7:15 ` [PATCH v4 15/18] btrfs: disk-io: introduce subpage metadata validation check Qu Wenruo
2021-01-16  7:15 ` [PATCH v4 16/18] btrfs: introduce btrfs_subpage for data inodes Qu Wenruo
2021-01-19 20:48   ` David Sterba
2021-01-20 15:28   ` Josef Bacik
2021-01-26  7:05     ` Qu Wenruo
2021-01-16  7:15 ` [PATCH v4 17/18] btrfs: integrate page status update for data read path into begin/end_page_read() Qu Wenruo
2021-01-20 15:41   ` Josef Bacik
2021-01-21  1:05     ` Qu Wenruo
2021-01-16  7:15 ` [PATCH v4 18/18] btrfs: allow RO mount of 4K sector size fs on 64K page system Qu Wenruo
2021-01-18 23:17 ` [PATCH v4 00/18] btrfs: add read-only support for subpage sector size David Sterba
2021-01-18 23:26   ` Qu Wenruo
2021-01-24 12:29     ` David Sterba
2021-01-25  1:19       ` Qu Wenruo

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