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write-back: fix nr_to_write counter

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Commit 05fe478dd0 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>
This commit is contained in:
Artem Bityutskiy 2009-02-02 18:33:49 +02:00 committed by Linus Torvalds
parent 5193535517
commit dcf6a79dda
1 changed files with 15 additions and 6 deletions
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21
mm/page-writeback.c
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@ -1051,13 +1051,22 @@ int write_cache_pages(struct address_space *mapping,
}
}
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;