On Tuesday 03 February 2009 19:42:22 Artem Bityutskiy wrote:
> 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;
> }
The commit you quote only moves nr_to_write to not take effect for
WB_SYNC_ALL (ie. data integrity) writeout. And makes no other change
to write_cache_pages.
I thought your problem might have been that you were calling this
with WB_SYNC_ALL and expecting it to heed nr_to_write, however...
> Also, I think wbc->nr_to_write should be changed in all cases, not only
> when wbc->sync_mode == WB_SYNC_NONE.
... you mention this here like it is an *additional* issue on top
of your problem. So I fail to see how my commit could have caused
this problem?
> 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.
And I don't know what you mean by this because the patch doesn't
fix any problem there AFAIKS.
Anyway, I did probably not pay enough attention to ubifs when making
this change, and if it wants wbc->nr_to_write updated even for data
integrity syncs, I don't see the harm in that. So I don't have any
objection to your patch. Thanks.
Can you cc stable@xxxxxxxxxx when a final version gets merged upstream
please?
>
> 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
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