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Message-Id: <1233655712.24809.101.camel@localhost.localdomain>
Date: Tue, 03 Feb 2009 12:08:32 +0200
From: Artem Bityutskiy <dedekind@...radead.org>
To: torvalds@...ux-foundation.org
Cc: Andrew Morton <akpm@...ux-foundation.org>,
Nick Piggin <npiggin@...e.de>,
Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
linux-fsdevel <linux-fsdevel@...r.kernel.org>
Subject: [BUGFIX take 2] [PATCH] write-back: fix nr_to_write counter
From: Artem Bityutskiy <Artem.Bityutskiy@...ia.com>
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. Here is the change from the commit:
--- a/mm/page-writeback.c
+++ b/mm/page-writeback.c
@@ -963,8 +963,10 @@ retry:
}
}
- if (--nr_to_write <= 0)
- done = 1;
+ if (wbc->sync_mode == WB_SYNC_NONE) {
+ if (--wbc->nr_to_write <= 0)
+ done = 1;
+ }
if (wbc->nonblocking && bdi_write_congested(bdi)) {
wbc->encountered_congestion = 1;
done = 1
}
It makes 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 des 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@...ia.com>
Acked-by: Nick Piggin <npiggin@...e.de>
Cc: Andrew Morton <akpm@...ux-foundation.org>
---
mm/page-writeback.c | 21 +++++++++++++++------
1 files changed, 15 insertions(+), 6 deletions(-)
diff --git a/mm/page-writeback.c b/mm/page-writeback.c
index b493db7..13a2b8e 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, bud 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;
--
1.6.0.6
--
Best regards,
Artem Bityutskiy (Битюцкий Артём)
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