dm thin: prefetch missing metadata pages

Prefetch metadata at the start of the worker thread and then again every
128th bio processed from the deferred list.

Signed-off-by: Joe Thornber <ejt@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>

3 files changed, 16 insertions, 4 deletions

diff --git a/drivers/md/dm-thin-metadata.c b/drivers/md/dm-thin-metadata.c
index ee42d1c52387..43adbb863f5a 100644
--- a/drivers/md/dm-thin-metadata.c
+++ b/drivers/md/dm-thin-metadata.c
@@ -1809,3 +1809,8 @@ bool dm_pool_metadata_needs_check(struct dm_pool_metadata *pmd)
 
         return needs_check;
 }
+
+void dm_pool_issue_prefetches(struct dm_pool_metadata *pmd)
+{
+        dm_tm_issue_prefetches(pmd->tm);
+}
diff --git a/drivers/md/dm-thin-metadata.h b/drivers/md/dm-thin-metadata.h
index efedd5a4cd8f..921d15ee56a0 100644
--- a/drivers/md/dm-thin-metadata.h
+++ b/drivers/md/dm-thin-metadata.h
@@ -213,6 +213,11 @@ int dm_pool_register_metadata_threshold(struct dm_pool_metadata *pmd,
 int dm_pool_metadata_set_needs_check(struct dm_pool_metadata *pmd);
 bool dm_pool_metadata_needs_check(struct dm_pool_metadata *pmd);
 
+/*
+ * Issue any prefetches that may be useful.
+ */
+void dm_pool_issue_prefetches(struct dm_pool_metadata *pmd);
+
 /*----------------------------------------------------------------*/
 
 #endif
diff --git a/drivers/md/dm-thin.c b/drivers/md/dm-thin.c
index eecfe7495232..97a7eb4d0412 100644
--- a/drivers/md/dm-thin.c
+++ b/drivers/md/dm-thin.c
@@ -1526,6 +1526,7 @@ static void process_thin_deferred_bios(struct thin_c *tc)
         struct bio *bio;
         struct bio_list bios;
         struct blk_plug plug;
+        unsigned count = 0;
 
         if (tc->requeue_mode) {
                 requeue_bio_list(tc, &tc->deferred_bio_list);
@@ -1567,6 +1568,10 @@ static void process_thin_deferred_bios(struct thin_c *tc)
                         pool->process_discard(tc, bio);
                 else
                         pool->process_bio(tc, bio);
+
+                if ((count++ & 127) == 0) {
+                        dm_pool_issue_prefetches(pool->pmd);
+                }
         }
         blk_finish_plug(&plug);
 }
@@ -1652,6 +1657,7 @@ static void do_worker(struct work_struct *ws)
 {
         struct pool *pool = container_of(ws, struct pool, worker);
 
+        dm_pool_issue_prefetches(pool->pmd);
         process_prepared(pool, &pool->prepared_mappings, &pool->process_prepared_mapping);
         process_prepared(pool, &pool->prepared_discards, &pool->process_prepared_discard);
         process_deferred_bios(pool);
@@ -1996,10 +2002,6 @@ static int thin_bio_map(struct dm_target *ti, struct bio *bio)
                 /* fall through */
 
         case -EWOULDBLOCK:
-                /*
-                 * In future, the failed dm_thin_find_block above could
-                 * provide the hint to load the metadata into cache.
-                 */
                 thin_defer_bio(tc, bio);
                 cell_defer_no_holder_no_free(tc, &cell1);
                 return DM_MAPIO_SUBMITTED;