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-rw-r--r--Documentation/device-mapper/cache.txt19
-rw-r--r--drivers/md/dm-cache-metadata.c5
-rw-r--r--drivers/md/dm-cache-metadata.h5
-rw-r--r--drivers/md/dm-cache-target.c209
4 files changed, 200 insertions, 38 deletions
diff --git a/Documentation/device-mapper/cache.txt b/Documentation/device-mapper/cache.txt
index 33d45ee0b737..ff6639f72536 100644
--- a/Documentation/device-mapper/cache.txt
+++ b/Documentation/device-mapper/cache.txt
@@ -68,10 +68,11 @@ So large block sizes are bad because they waste cache space. And small
block sizes are bad because they increase the amount of metadata (both
in core and on disk).
-Writeback/writethrough
-----------------------
+Cache operating modes
+---------------------
-The cache has two modes, writeback and writethrough.
+The cache has three operating modes: writeback, writethrough and
+passthrough.
If writeback, the default, is selected then a write to a block that is
cached will go only to the cache and the block will be marked dirty in
@@ -81,6 +82,18 @@ If writethrough is selected then a write to a cached block will not
complete until it has hit both the origin and cache devices. Clean
blocks should remain clean.
+If passthrough is selected, useful when the cache contents are not known
+to be coherent with the origin device, then all reads are served from
+the origin device (all reads miss the cache) and all writes are
+forwarded to the origin device; additionally, write hits cause cache
+block invalidates. Passthrough mode allows a cache device to be
+activated without having to worry about coherency. Coherency that
+exists is maintained, although the cache will gradually cool as writes
+take place. If the coherency of the cache can later be verified, or
+established, the cache device can can be transitioned to writethrough or
+writeback mode while still warm. Otherwise, the cache contents can be
+discarded prior to transitioning to the desired operating mode.
+
A simple cleaner policy is provided, which will clean (write back) all
dirty blocks in a cache. Useful for decommissioning a cache.
diff --git a/drivers/md/dm-cache-metadata.c b/drivers/md/dm-cache-metadata.c
index 062b83ed3e84..8601425436cd 100644
--- a/drivers/md/dm-cache-metadata.c
+++ b/drivers/md/dm-cache-metadata.c
@@ -1249,3 +1249,8 @@ int dm_cache_save_hint(struct dm_cache_metadata *cmd, dm_cblock_t cblock,
return r;
}
+
+int dm_cache_metadata_all_clean(struct dm_cache_metadata *cmd, bool *result)
+{
+ return blocks_are_unmapped_or_clean(cmd, 0, cmd->cache_blocks, result);
+}
diff --git a/drivers/md/dm-cache-metadata.h b/drivers/md/dm-cache-metadata.h
index f45cef21f3d0..cd906f14f98d 100644
--- a/drivers/md/dm-cache-metadata.h
+++ b/drivers/md/dm-cache-metadata.h
@@ -137,6 +137,11 @@ int dm_cache_begin_hints(struct dm_cache_metadata *cmd, struct dm_cache_policy *
int dm_cache_save_hint(struct dm_cache_metadata *cmd,
dm_cblock_t cblock, uint32_t hint);
+/*
+ * Query method. Are all the blocks in the cache clean?
+ */
+int dm_cache_metadata_all_clean(struct dm_cache_metadata *cmd, bool *result);
+
/*----------------------------------------------------------------*/
#endif /* DM_CACHE_METADATA_H */
diff --git a/drivers/md/dm-cache-target.c b/drivers/md/dm-cache-target.c
index 183dfc9db297..8c0217753cc5 100644
--- a/drivers/md/dm-cache-target.c
+++ b/drivers/md/dm-cache-target.c
@@ -104,14 +104,37 @@ static void dm_unhook_bio(struct dm_hook_info *h, struct bio *bio)
/*
* FIXME: the cache is read/write for the time being.
*/
-enum cache_mode {
+enum cache_metadata_mode {
CM_WRITE, /* metadata may be changed */
CM_READ_ONLY, /* metadata may not be changed */
};
+enum cache_io_mode {
+ /*
+ * Data is written to cached blocks only. These blocks are marked
+ * dirty. If you lose the cache device you will lose data.
+ * Potential performance increase for both reads and writes.
+ */
+ CM_IO_WRITEBACK,
+
+ /*
+ * Data is written to both cache and origin. Blocks are never
+ * dirty. Potential performance benfit for reads only.
+ */
+ CM_IO_WRITETHROUGH,
+
+ /*
+ * A degraded mode useful for various cache coherency situations
+ * (eg, rolling back snapshots). Reads and writes always go to the
+ * origin. If a write goes to a cached oblock, then the cache
+ * block is invalidated.
+ */
+ CM_IO_PASSTHROUGH
+};
+
struct cache_features {
- enum cache_mode mode;
- bool write_through:1;
+ enum cache_metadata_mode mode;
+ enum cache_io_mode io_mode;
};
struct cache_stats {
@@ -565,9 +588,24 @@ static void save_stats(struct cache *cache)
#define PB_DATA_SIZE_WB (offsetof(struct per_bio_data, cache))
#define PB_DATA_SIZE_WT (sizeof(struct per_bio_data))
+static bool writethrough_mode(struct cache_features *f)
+{
+ return f->io_mode == CM_IO_WRITETHROUGH;
+}
+
+static bool writeback_mode(struct cache_features *f)
+{
+ return f->io_mode == CM_IO_WRITEBACK;
+}
+
+static bool passthrough_mode(struct cache_features *f)
+{
+ return f->io_mode == CM_IO_PASSTHROUGH;
+}
+
static size_t get_per_bio_data_size(struct cache *cache)
{
- return cache->features.write_through ? PB_DATA_SIZE_WT : PB_DATA_SIZE_WB;
+ return writethrough_mode(&cache->features) ? PB_DATA_SIZE_WT : PB_DATA_SIZE_WB;
}
static struct per_bio_data *get_per_bio_data(struct bio *bio, size_t data_size)
@@ -1135,6 +1173,32 @@ static void demote_then_promote(struct cache *cache, struct prealloc *structs,
quiesce_migration(mg);
}
+/*
+ * Invalidate a cache entry. No writeback occurs; any changes in the cache
+ * block are thrown away.
+ */
+static void invalidate(struct cache *cache, struct prealloc *structs,
+ dm_oblock_t oblock, dm_cblock_t cblock,
+ struct dm_bio_prison_cell *cell)
+{
+ struct dm_cache_migration *mg = prealloc_get_migration(structs);
+
+ mg->err = false;
+ mg->writeback = false;
+ mg->demote = true;
+ mg->promote = false;
+ mg->requeue_holder = true;
+ mg->cache = cache;
+ mg->old_oblock = oblock;
+ mg->cblock = cblock;
+ mg->old_ocell = cell;
+ mg->new_ocell = NULL;
+ mg->start_jiffies = jiffies;
+
+ inc_nr_migrations(cache);
+ quiesce_migration(mg);
+}
+
/*----------------------------------------------------------------
* bio processing
*--------------------------------------------------------------*/
@@ -1197,13 +1261,6 @@ static bool spare_migration_bandwidth(struct cache *cache)
return current_volume < cache->migration_threshold;
}
-static bool is_writethrough_io(struct cache *cache, struct bio *bio,
- dm_cblock_t cblock)
-{
- return bio_data_dir(bio) == WRITE &&
- cache->features.write_through && !is_dirty(cache, cblock);
-}
-
static void inc_hit_counter(struct cache *cache, struct bio *bio)
{
atomic_inc(bio_data_dir(bio) == READ ?
@@ -1216,6 +1273,15 @@ static void inc_miss_counter(struct cache *cache, struct bio *bio)
&cache->stats.read_miss : &cache->stats.write_miss);
}
+static void issue_cache_bio(struct cache *cache, struct bio *bio,
+ struct per_bio_data *pb,
+ dm_oblock_t oblock, dm_cblock_t cblock)
+{
+ pb->all_io_entry = dm_deferred_entry_inc(cache->all_io_ds);
+ remap_to_cache_dirty(cache, bio, oblock, cblock);
+ issue(cache, bio);
+}
+
static void process_bio(struct cache *cache, struct prealloc *structs,
struct bio *bio)
{
@@ -1227,7 +1293,8 @@ static void process_bio(struct cache *cache, struct prealloc *structs,
size_t pb_data_size = get_per_bio_data_size(cache);
struct per_bio_data *pb = get_per_bio_data(bio, pb_data_size);
bool discarded_block = is_discarded_oblock(cache, block);
- bool can_migrate = discarded_block || spare_migration_bandwidth(cache);
+ bool passthrough = passthrough_mode(&cache->features);
+ bool can_migrate = !passthrough && (discarded_block || spare_migration_bandwidth(cache));
/*
* Check to see if that block is currently migrating.
@@ -1248,15 +1315,39 @@ static void process_bio(struct cache *cache, struct prealloc *structs,
switch (lookup_result.op) {
case POLICY_HIT:
- inc_hit_counter(cache, bio);
- pb->all_io_entry = dm_deferred_entry_inc(cache->all_io_ds);
+ if (passthrough) {
+ inc_miss_counter(cache, bio);
- if (is_writethrough_io(cache, bio, lookup_result.cblock))
- remap_to_origin_then_cache(cache, bio, block, lookup_result.cblock);
- else
- remap_to_cache_dirty(cache, bio, block, lookup_result.cblock);
+ /*
+ * Passthrough always maps to the origin,
+ * invalidating any cache blocks that are written
+ * to.
+ */
+
+ if (bio_data_dir(bio) == WRITE) {
+ atomic_inc(&cache->stats.demotion);
+ invalidate(cache, structs, block, lookup_result.cblock, new_ocell);
+ release_cell = false;
+
+ } else {
+ /* FIXME: factor out issue_origin() */
+ pb->all_io_entry = dm_deferred_entry_inc(cache->all_io_ds);
+ remap_to_origin_clear_discard(cache, bio, block);
+ issue(cache, bio);
+ }
+ } else {
+ inc_hit_counter(cache, bio);
+
+ if (bio_data_dir(bio) == WRITE &&
+ writethrough_mode(&cache->features) &&
+ !is_dirty(cache, lookup_result.cblock)) {
+ pb->all_io_entry = dm_deferred_entry_inc(cache->all_io_ds);
+ remap_to_origin_then_cache(cache, bio, block, lookup_result.cblock);
+ issue(cache, bio);
+ } else
+ issue_cache_bio(cache, bio, pb, block, lookup_result.cblock);
+ }
- issue(cache, bio);
break;
case POLICY_MISS:
@@ -1807,7 +1898,7 @@ static int parse_block_size(struct cache_args *ca, struct dm_arg_set *as,
static void init_features(struct cache_features *cf)
{
cf->mode = CM_WRITE;
- cf->write_through = false;
+ cf->io_mode = CM_IO_WRITEBACK;
}
static int parse_features(struct cache_args *ca, struct dm_arg_set *as,
@@ -1832,10 +1923,13 @@ static int parse_features(struct cache_args *ca, struct dm_arg_set *as,
arg = dm_shift_arg(as);
if (!strcasecmp(arg, "writeback"))
- cf->write_through = false;
+ cf->io_mode = CM_IO_WRITEBACK;
else if (!strcasecmp(arg, "writethrough"))
- cf->write_through = true;
+ cf->io_mode = CM_IO_WRITETHROUGH;
+
+ else if (!strcasecmp(arg, "passthrough"))
+ cf->io_mode = CM_IO_PASSTHROUGH;
else {
*error = "Unrecognised cache feature requested";
@@ -2088,6 +2182,22 @@ static int cache_create(struct cache_args *ca, struct cache **result)
}
cache->cmd = cmd;
+ if (passthrough_mode(&cache->features)) {
+ bool all_clean;
+
+ r = dm_cache_metadata_all_clean(cache->cmd, &all_clean);
+ if (r) {
+ *error = "dm_cache_metadata_all_clean() failed";
+ goto bad;
+ }
+
+ if (!all_clean) {
+ *error = "Cannot enter passthrough mode unless all blocks are clean";
+ r = -EINVAL;
+ goto bad;
+ }
+ }
+
spin_lock_init(&cache->lock);
bio_list_init(&cache->deferred_bios);
bio_list_init(&cache->deferred_flush_bios);
@@ -2303,17 +2413,37 @@ static int cache_map(struct dm_target *ti, struct bio *bio)
return DM_MAPIO_SUBMITTED;
}
+ r = DM_MAPIO_REMAPPED;
switch (lookup_result.op) {
case POLICY_HIT:
- inc_hit_counter(cache, bio);
- pb->all_io_entry = dm_deferred_entry_inc(cache->all_io_ds);
+ if (passthrough_mode(&cache->features)) {
+ if (bio_data_dir(bio) == WRITE) {
+ /*
+ * We need to invalidate this block, so
+ * defer for the worker thread.
+ */
+ cell_defer(cache, cell, true);
+ r = DM_MAPIO_SUBMITTED;
+
+ } else {
+ pb->all_io_entry = dm_deferred_entry_inc(cache->all_io_ds);
+ inc_miss_counter(cache, bio);
+ remap_to_origin_clear_discard(cache, bio, block);
+
+ cell_defer(cache, cell, false);
+ }
- if (is_writethrough_io(cache, bio, lookup_result.cblock))
- remap_to_origin_then_cache(cache, bio, block, lookup_result.cblock);
- else
- remap_to_cache_dirty(cache, bio, block, lookup_result.cblock);
+ } else {
+ inc_hit_counter(cache, bio);
+
+ if (bio_data_dir(bio) == WRITE && writethrough_mode(&cache->features) &&
+ !is_dirty(cache, lookup_result.cblock))
+ remap_to_origin_then_cache(cache, bio, block, lookup_result.cblock);
+ else
+ remap_to_cache_dirty(cache, bio, block, lookup_result.cblock);
- cell_defer(cache, cell, false);
+ cell_defer(cache, cell, false);
+ }
break;
case POLICY_MISS:
@@ -2338,10 +2468,10 @@ static int cache_map(struct dm_target *ti, struct bio *bio)
DMERR_LIMIT("%s: erroring bio: unknown policy op: %u", __func__,
(unsigned) lookup_result.op);
bio_io_error(bio);
- return DM_MAPIO_SUBMITTED;
+ r = DM_MAPIO_SUBMITTED;
}
- return DM_MAPIO_REMAPPED;
+ return r;
}
static int cache_end_io(struct dm_target *ti, struct bio *bio, int error)
@@ -2659,10 +2789,19 @@ static void cache_status(struct dm_target *ti, status_type_t type,
(unsigned long long) from_cblock(residency),
cache->nr_dirty);
- if (cache->features.write_through)
+ if (writethrough_mode(&cache->features))
DMEMIT("1 writethrough ");
- else
- DMEMIT("0 ");
+
+ else if (passthrough_mode(&cache->features))
+ DMEMIT("1 passthrough ");
+
+ else if (writeback_mode(&cache->features))
+ DMEMIT("1 writeback ");
+
+ else {
+ DMERR("internal error: unknown io mode: %d", (int) cache->features.io_mode);
+ goto err;
+ }
DMEMIT("2 migration_threshold %llu ", (unsigned long long) cache->migration_threshold);
if (sz < maxlen) {
@@ -2771,7 +2910,7 @@ static void cache_io_hints(struct dm_target *ti, struct queue_limits *limits)
static struct target_type cache_target = {
.name = "cache",
- .version = {1, 1, 1},
+ .version = {1, 2, 0},
.module = THIS_MODULE,
.ctr = cache_ctr,
.dtr = cache_dtr,
generated by cgit (git 2.34.1) at 2024-06-15 03:11:07 +0000