Commit dcf6a79d authored Feb 02, 2009 by Artem Bityutskiy Committed by Linus Torvalds Feb 03, 2009

write-back: fix nr_to_write counter



Commit 05fe478d introduced some
@wbc->nr_to_write breakage.

It made the following changes:
 1. Decrement wbc->nr_to_write instead of nr_to_write
 2. Decrement wbc->nr_to_write _only_ if wbc->sync_mode == WB_SYNC_NONE
 3. If synced nr_to_write pages, stop only if if wbc->sync_mode ==
    WB_SYNC_NONE, otherwise keep going.

However, according to the commit message, the intention was to only make
change 3.  Change 1 is a bug.  Change 2 does not seem to be necessary,
and it breaks UBIFS expectations, so if needed, it should be done
separately later.  And change 2 does not seem to be documented in the
commit message.

This patch does the following:
 1. Undo changes 1 and 2
 2. Add a comment explaining change 3 (it very useful to have comments
    in _code_, not only in the commit).

Signed-off-by: Artem Bityutskiy <Artem.Bityutskiy@nokia.com>
Acked-by: Nick Piggin <npiggin@suse.de>
Cc: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

parent 51935355

mm/page-writeback.c

+15 −6

Original line number	Diff line number	Diff line
		@@ -1051,13 +1051,22 @@ continue_unlock:
		}
		}

		if (wbc->sync_mode == WB_SYNC_NONE) {
		wbc->nr_to_write--;
		if (wbc->nr_to_write <= 0) {
		if (nr_to_write > 0)
		nr_to_write--;
		else if (wbc->sync_mode == WB_SYNC_NONE) {
		/*
		* We stop writing back only if we are not
		* doing integrity sync. In case of integrity
		* sync we have to keep going because someone
		* may be concurrently dirtying pages, and we
		* might have synced a lot of newly appeared
		* dirty pages, but have not synced all of the
		* old dirty pages.
		*/
		done = 1;
		break;
		}
		}

		if (wbc->nonblocking && bdi_write_congested(bdi)) {
		wbc->encountered_congestion = 1;
		done = 1;

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