Commit a297b2fc authored Feb 10, 2019 by Xiaoguang Wang Committed by Theodore Ts'o Feb 10, 2019

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>

parent 16e08b14

fs/ext4/inode.c

+5 −4

Original line number	Diff line number	Diff line
		@@ -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

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