On Tue, 2009-02-03 at 12:08 +0200, Artem Bityutskiy wrote:
> 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 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
> }
Actually quoting a patch in the description in this manner will make the
patch fail to apply (or fail to apply correctly). If you must quote the
patch, you should probably prepend ">" or something.
> 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@xxxxxxxxx>
> Acked-by: Nick Piggin <npiggin@xxxxxxx>
> Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> ---
> 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
>
>
--
David Kleikamp
IBM Linux Technology Center
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