This patch modifies dm-snapshot so that it prefetches the buffers when
loading the exceptions.
The number of buffers read ahead is specified in the DM_PREFETCH_CHUNKS
macro.
Signed-off-by: Mikulas Patocka <mpatocka@xxxxxxxxxx>
---
drivers/md/dm-snap-persistent.c | 22 +++++++++++++++++++++-
1 file changed, 21 insertions(+), 1 deletion(-)
Index: linux-3.13-rc7/drivers/md/dm-snap-persistent.c
===================================================================
--- linux-3.13-rc7.orig/drivers/md/dm-snap-persistent.c 2014-01-14 00:54:52.000000000 +0100
+++ linux-3.13-rc7/drivers/md/dm-snap-persistent.c 2014-01-14 00:56:39.000000000 +0100
@@ -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.
@@ -496,6 +498,7 @@ static int read_exceptions(struct pstore
{
int r, full = 1;
struct dm_bufio_client *client;
+ chunk_t prefetch_area = 0;
client = dm_bufio_client_create(dm_snap_cow(ps->store->snap)->bdev,
ps->store->chunk_size << SECTOR_SHIFT,
@@ -504,6 +507,8 @@ static int read_exceptions(struct pstore
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.
@@ -511,7 +516,22 @@ static int read_exceptions(struct pstore
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;
+
+ if (unlikely(prefetch_area < ps->current_area))
+ prefetch_area = ps->current_area;
+
+ if (DM_PREFETCH_CHUNKS) do {
+ chunk_t pf_chunk = area_location(ps, prefetch_area);
+ if (unlikely(pf_chunk >= dm_bufio_get_device_size(client)))
+ break;
+ dm_bufio_prefetch(client, pf_chunk, 1);
+ prefetch_area++;
+ if (unlikely(!prefetch_area))
+ break;
+ } while (prefetch_area <= ps->current_area + DM_PREFETCH_CHUNKS);
+
+ chunk = area_location(ps, ps->current_area);
area = dm_bufio_read(client, chunk, &bp);
if (unlikely(IS_ERR(area))) {
--
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