Hi,
commit 05fe478dd04e02fa230c305ab9b5616669821dd3
Author: Nick Piggin <npiggin@xxxxxxx>
Date: Tue Jan 6 14:39:08 2009 -0800
mm: write_cache_pages integrity fix
broke wbc->nr_to_write handling. Here is the fix.
I'm not 100% sure I got things right, because I am far not expert in the
area. Please, review it. The patch fixes my UBIFS issues, which are
caused by the fact that wbc->nr_to_write is not updated.
======================================================================
From: Artem Bityutskiy <Artem.Bityutskiy@xxxxxxxxx>
Date: Mon, 2 Feb 2009 18:33:49 +0200
Subject: [PATCH] write-back: fix nr_to_write counter
Commit 05fe478dd04e02fa230c305ab9b5616669821dd3 broke @wbc->nr_to_write.
'write_cache_pages()' changes it in the loop, but restores the original
value from @nr_to_write at the end, because of this code:
if (!wbc->no_nrwrite_index_update) {
if (wbc->range_cyclic || (range_whole && nr_to_write > 0))
mapping->writeback_index = done_index;
wbc->nr_to_write = nr_to_write;
}
Well, in case of @wbc->no_nrwrite_index_update != 0, we do change
wbc->nr_to_write, while we should not. This patch fixes this behavior.
Also, I think wbc->nr_to_write should be changed in all cases, not only
when wbc->sync_mode == WB_SYNC_NONE.
Also, I add a comment explaining why we do not stop writing back.
Signed-off-by: Artem Bityutskiy <Artem.Bityutskiy@xxxxxxxxx>
---
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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