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dm cache: add support for discard passdown to the origin device
DM cache now defaults to passing discards down to the origin device. User may disable this using the "no_discard_passdown" feature when creating the cache device. If the cache's underlying origin device doesn't support discards then passdown is disabled (with warning). Similarly, if the underlying origin device's max_discard_sectors is less than a cache block discard passdown will be disabled (this is required because sizing of the cache internal discard bitset depends on it). Signed-off-by: Mike Snitzer <snitzer@redhat.com>
This commit is contained in:
Mike Snitzer
parent
f87e033b3b
commit
de7180ff90
@ -206,6 +206,9 @@ Optional feature arguments are:
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in a separate btree, which improves speed of shutting
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down the cache.
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no_discard_passdown : disable passing down discards from the cache
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to the origin's data device.
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A policy called 'default' is always registered. This is an alias for
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the policy we currently think is giving best all round performance.
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@ -353,6 +353,7 @@ struct cache_features {
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enum cache_metadata_mode mode;
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enum cache_io_mode io_mode;
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unsigned metadata_version;
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bool discard_passdown:1;
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};
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struct cache_stats {
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@ -1899,7 +1900,11 @@ static bool process_discard_bio(struct cache *cache, struct bio *bio)
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b = to_dblock(from_dblock(b) + 1);
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}
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bio_endio(bio);
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if (cache->features.discard_passdown) {
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remap_to_origin(cache, bio);
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generic_make_request(bio);
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} else
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bio_endio(bio);
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return false;
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}
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@ -2233,13 +2238,14 @@ static void init_features(struct cache_features *cf)
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cf->mode = CM_WRITE;
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cf->io_mode = CM_IO_WRITEBACK;
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cf->metadata_version = 1;
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cf->discard_passdown = true;
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}
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static int parse_features(struct cache_args *ca, struct dm_arg_set *as,
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char **error)
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{
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static const struct dm_arg _args[] = {
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{0, 2, "Invalid number of cache feature arguments"},
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{0, 3, "Invalid number of cache feature arguments"},
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};
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int r, mode_ctr = 0;
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@ -2274,6 +2280,9 @@ static int parse_features(struct cache_args *ca, struct dm_arg_set *as,
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else if (!strcasecmp(arg, "metadata2"))
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cf->metadata_version = 2;
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else if (!strcasecmp(arg, "no_discard_passdown"))
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cf->discard_passdown = false;
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else {
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*error = "Unrecognised cache feature requested";
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return -EINVAL;
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@ -3119,6 +3128,39 @@ static void cache_resume(struct dm_target *ti)
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do_waker(&cache->waker.work);
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}
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static void emit_flags(struct cache *cache, char *result,
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unsigned maxlen, ssize_t *sz_ptr)
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{
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ssize_t sz = *sz_ptr;
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struct cache_features *cf = &cache->features;
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unsigned count = (cf->metadata_version == 2) + !cf->discard_passdown + 1;
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DMEMIT("%u ", count);
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if (cf->metadata_version == 2)
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DMEMIT("metadata2 ");
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if (writethrough_mode(cache))
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DMEMIT("writethrough ");
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else if (passthrough_mode(cache))
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DMEMIT("passthrough ");
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else if (writeback_mode(cache))
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DMEMIT("writeback ");
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else {
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DMEMIT("unknown ");
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DMERR("%s: internal error: unknown io mode: %d",
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cache_device_name(cache), (int) cf->io_mode);
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}
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if (!cf->discard_passdown)
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DMEMIT("no_discard_passdown ");
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*sz_ptr = sz;
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}
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/*
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* Status format:
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*
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@ -3185,25 +3227,7 @@ static void cache_status(struct dm_target *ti, status_type_t type,
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(unsigned) atomic_read(&cache->stats.promotion),
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(unsigned long) atomic_read(&cache->nr_dirty));
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if (cache->features.metadata_version == 2)
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DMEMIT("2 metadata2 ");
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else
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DMEMIT("1 ");
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if (writethrough_mode(cache))
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DMEMIT("writethrough ");
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else if (passthrough_mode(cache))
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DMEMIT("passthrough ");
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else if (writeback_mode(cache))
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DMEMIT("writeback ");
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else {
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DMERR("%s: internal error: unknown io mode: %d",
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cache_device_name(cache), (int) cache->features.io_mode);
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goto err;
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}
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emit_flags(cache, result, maxlen, &sz);
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DMEMIT("2 migration_threshold %llu ", (unsigned long long) cache->migration_threshold);
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@ -3432,14 +3456,62 @@ static int cache_iterate_devices(struct dm_target *ti,
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return r;
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}
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static bool origin_dev_supports_discard(struct block_device *origin_bdev)
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{
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struct request_queue *q = bdev_get_queue(origin_bdev);
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return q && blk_queue_discard(q);
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}
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/*
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* If discard_passdown was enabled verify that the origin device
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* supports discards. Disable discard_passdown if not.
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*/
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static void disable_passdown_if_not_supported(struct cache *cache)
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{
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struct block_device *origin_bdev = cache->origin_dev->bdev;
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struct queue_limits *origin_limits = &bdev_get_queue(origin_bdev)->limits;
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const char *reason = NULL;
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char buf[BDEVNAME_SIZE];
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if (!cache->features.discard_passdown)
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return;
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if (!origin_dev_supports_discard(origin_bdev))
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reason = "discard unsupported";
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else if (origin_limits->max_discard_sectors < cache->sectors_per_block)
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reason = "max discard sectors smaller than a block";
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if (reason) {
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DMWARN("Origin device (%s) %s: Disabling discard passdown.",
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bdevname(origin_bdev, buf), reason);
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cache->features.discard_passdown = false;
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}
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}
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static void set_discard_limits(struct cache *cache, struct queue_limits *limits)
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{
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struct block_device *origin_bdev = cache->origin_dev->bdev;
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struct queue_limits *origin_limits = &bdev_get_queue(origin_bdev)->limits;
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if (!cache->features.discard_passdown) {
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/* No passdown is done so setting own virtual limits */
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limits->max_discard_sectors = min_t(sector_t, cache->discard_block_size * 1024,
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cache->origin_sectors);
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limits->discard_granularity = cache->discard_block_size << SECTOR_SHIFT;
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return;
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}
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/*
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* FIXME: these limits may be incompatible with the cache device
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* cache_iterate_devices() is stacking both origin and fast device limits
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* but discards aren't passed to fast device, so inherit origin's limits.
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*/
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limits->max_discard_sectors = min_t(sector_t, cache->discard_block_size * 1024,
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cache->origin_sectors);
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limits->discard_granularity = cache->discard_block_size << SECTOR_SHIFT;
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limits->max_discard_sectors = origin_limits->max_discard_sectors;
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limits->max_hw_discard_sectors = origin_limits->max_hw_discard_sectors;
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limits->discard_granularity = origin_limits->discard_granularity;
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limits->discard_alignment = origin_limits->discard_alignment;
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limits->discard_misaligned = origin_limits->discard_misaligned;
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}
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static void cache_io_hints(struct dm_target *ti, struct queue_limits *limits)
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@ -3456,6 +3528,8 @@ static void cache_io_hints(struct dm_target *ti, struct queue_limits *limits)
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blk_limits_io_min(limits, cache->sectors_per_block << SECTOR_SHIFT);
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blk_limits_io_opt(limits, cache->sectors_per_block << SECTOR_SHIFT);
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}
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disable_passdown_if_not_supported(cache);
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set_discard_limits(cache, limits);
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}
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@ -3463,7 +3537,7 @@ static void cache_io_hints(struct dm_target *ti, struct queue_limits *limits)
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static struct target_type cache_target = {
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.name = "cache",
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.version = {2, 0, 0},
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.version = {2, 1, 0},
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.module = THIS_MODULE,
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.ctr = cache_ctr,
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.dtr = cache_dtr,
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