Re: [PATCH] dm writecache: skip writecache_wait for pmem mode
From: Mikulas Patocka
Date: Wed Sep 04 2019 - 04:48:38 EST
On Mon, 2 Sep 2019, Huaisheng Ye wrote:
> From: Huaisheng Ye <yehs1@xxxxxxxxxx>
> The array bio_in_progress only have chance to be increased and
> decreased with ssd mode. For pmem mode, they are not involved at all.
> So skip writecache_wait_for_ios in writecache_flush for pmem.
> Suggested-by: Doris Yu <tyu1@xxxxxxxxxx>
> Signed-off-by: Huaisheng Ye <yehs1@xxxxxxxxxx>
> drivers/md/dm-writecache.c | 3 ++-
> 1 file changed, 2 insertions(+), 1 deletion(-)
> diff --git a/drivers/md/dm-writecache.c b/drivers/md/dm-writecache.c
> index c481947..d06b8aa 100644
> --- a/drivers/md/dm-writecache.c
> +++ b/drivers/md/dm-writecache.c
> @@ -726,7 +726,8 @@ static void writecache_flush(struct dm_writecache *wc)
> - writecache_wait_for_ios(wc, WRITE);
> + if (!WC_MODE_PMEM(wc))
> + writecache_wait_for_ios(wc, WRITE);
> pmem_assign(sb(wc)->seq_count, cpu_to_le64(wc->seq_count));
I think this is not needed - wait_event in writecache_wait_for_ios exits
immediatelly if the condition is true.
This code path is not so hot that we would need microoptimizations like
this to avoid function calls.