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
--
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