No.
This changed patch inefficiently loops in bufio_prefetch_chunks for each
buffer that is read.
Mikulas
On Mon, 13 Jan 2014, Mike Snitzer wrote:
> From: Mikulas Patocka <mpatocka@xxxxxxxxxx>
>
> This patch modifies dm-snapshot so that it prefetches the buffers when
> loading the exceptions.
>
> The number of chunk-sized buffers read ahead is specified in the
> DM_PREFETCH_CHUNKS macro. The current default for DM_PREFETCH_CHUNKS
> (12) may need to be adjusted to improve performance on different types
> of storage -- a future patch should make this configurable.
>
> Signed-off-by: Mikulas Patocka <mpatocka@xxxxxxxxxx>
> Signed-off-by: Mike Snitzer <snitzer@xxxxxxxxxx>
> ---
> drivers/md/dm-snap-persistent.c | 34 +++++++++++++++++++++++++++++++++-
> 1 files changed, 33 insertions(+), 1 deletions(-)
>
> diff --git a/drivers/md/dm-snap-persistent.c b/drivers/md/dm-snap-persistent.c
> index 1692750..ea45b3b 100644
> --- a/drivers/md/dm-snap-persistent.c
> +++ b/drivers/md/dm-snap-persistent.c
> @@ -18,6 +18,8 @@
> #define DM_MSG_PREFIX "persistent snapshot"
> #define DM_CHUNK_SIZE_DEFAULT_SECTORS 32 /* 16KB */
>
> +#define DM_PREFETCH_CHUNKS 12
> +
> /*-----------------------------------------------------------------
> * Persistent snapshots, by persistent we mean that the snapshot
> * will survive a reboot.
> @@ -490,6 +492,30 @@ static int insert_exceptions(struct pstore *ps, void *ps_area,
> return 0;
> }
>
> +static void bufio_prefetch_chunks(struct dm_bufio_client *client,
> + struct pstore *ps)
> +{
> + chunk_t prefetch_area = 0;
> + chunk_t pf_chunk;
> +
> + if (!DM_PREFETCH_CHUNKS)
> + return;
> +
> + if (prefetch_area < ps->current_area)
> + prefetch_area = ps->current_area;
> +
> + do {
> + pf_chunk = area_location(ps, prefetch_area);
> + if (unlikely(pf_chunk >= dm_bufio_get_device_size(client)))
> + break;
> + if (unlikely(!dm_bufio_prefetch(client, pf_chunk, 1)))
> + break;
> + prefetch_area++;
> + if (unlikely(!prefetch_area))
> + break;
> + } while (prefetch_area <= ps->current_area + DM_PREFETCH_CHUNKS);
> +}
> +
> static int read_exceptions(struct pstore *ps,
> int (*callback)(void *callback_context, chunk_t old,
> chunk_t new),
> @@ -505,6 +531,8 @@ static int read_exceptions(struct pstore *ps,
> if (IS_ERR(client))
> return PTR_ERR(client);
>
> + dm_bufio_set_minimum_buffers(client, DM_PREFETCH_CHUNKS + 1);
> +
> /*
> * Keeping reading chunks and inserting exceptions until
> * we find a partially full area.
> @@ -512,7 +540,11 @@ static int read_exceptions(struct pstore *ps,
> for (ps->current_area = 0; full; ps->current_area++) {
> struct dm_buffer *bp;
> void *area;
> - chunk_t chunk = area_location(ps, ps->current_area);
> + chunk_t chunk;
> +
> + bufio_prefetch_chunks(client, ps);
> +
> + chunk = area_location(ps, ps->current_area);
>
> area = dm_bufio_read(client, chunk, &bp);
> if (unlikely(IS_ERR(area))) {
> --
> 1.7.4.4
>
--
dm-devel mailing list
dm-devel@xxxxxxxxxx
https://www.redhat.com/mailman/listinfo/dm-devel
