From dcf6a79dda5cc2a2bec183e50d829030c0972aaa Mon Sep 17 00:00:00 2001 From: Artem Bityutskiy Date: Mon, 2 Feb 2009 18:33:49 +0200 Subject: [PATCH] write-back: fix nr_to_write counter Commit 05fe478dd04e02fa230c305ab9b5616669821dd3 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 Acked-by: Nick Piggin Cc: Andrew Morton Signed-off-by: Linus Torvalds --- mm/page-writeback.c | 21 +++++++++++++++------ 1 file changed, 15 insertions(+), 6 deletions(-) diff --git a/mm/page-writeback.c b/mm/page-writeback.c index b493db7841dc..dc32dae01e5f 100644 --- a/mm/page-writeback.c +++ b/mm/page-writeback.c @@ -1051,13 +1051,22 @@ continue_unlock: } } - if (wbc->sync_mode == WB_SYNC_NONE) { - wbc->nr_to_write--; - if (wbc->nr_to_write <= 0) { - done = 1; - break; - } + 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; -- 2.20.1