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ext4: unlock unused_pages timely when doing writeback 

In mpage_add_bh_to_extent(), when accumulated extents length is greater
than MAX_WRITEPAGES_EXTENT_LEN or buffer head's b_stat is not equal, we
will not continue to search unmapped area for this page, but note this
page is locked, and will only be unlocked in mpage_release_unused_pages()
after ext4_io_submit, if io also is throttled by blk-throttle or similar
io qos, we will hold this page locked for a while, it's unnecessary.

I think the best fix is to refactor mpage_add_bh_to_extent() to let it
return some hints whether to unlock this page, but given that we will
improve dioread_nolock later, we can let it done later, so currently
the simple fix would just call mpage_release_unused_pages() before
ext4_io_submit().

Signed-off-by: Xiaoguang Wang <xiaoguang.wang@linux.alibaba.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
This commit is contained in:
Xiaoguang Wang 2019-02-10 23:53:21 -05:00 committed by Theodore Ts'o
parent 16e08b14a4
commit a297b2fcee
1 changed files with 5 additions and 4 deletions
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9
fs/ext4/inode.c
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@ -2829,12 +2829,12 @@ retry:
goto unplug;
}
ret = mpage_prepare_extent_to_map(&mpd);
/* Unlock pages we didn't use */
mpage_release_unused_pages(&mpd, false);
/* Submit prepared bio */
ext4_io_submit(&mpd.io_submit);
ext4_put_io_end_defer(mpd.io_submit.io_end);
mpd.io_submit.io_end = NULL;
/* Unlock pages we didn't use */
mpage_release_unused_pages(&mpd, false);
if (ret < 0)
goto unplug;
@ -2902,10 +2902,11 @@ retry:
handle = NULL;
mpd.do_map = 0;
}
/* Submit prepared bio */
ext4_io_submit(&mpd.io_submit);
/* Unlock pages we didn't use */
mpage_release_unused_pages(&mpd, give_up_on_write);
/* Submit prepared bio */
ext4_io_submit(&mpd.io_submit);
/*
* Drop our io_end reference we got from init. We have
* to be careful and use deferred io_end finishing if