dm cache: cache shrinking support

Allow a cache to shrink if the blocks being removed from the cache are
not dirty.

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

diff --git a/drivers/md/dm-cache-metadata.c b/drivers/md/dm-cache-metadata.c
index 2262b4e57a28afec2811b11d42b4a6f84328705a..062b83ed3e846aa15bf357069e33e841624b50d0 100644 (file)
--- a/drivers/md/dm-cache-metadata.c
+++ b/drivers/md/dm-cache-metadata.c
@@ -667,19 +667,85 @@ void dm_cache_metadata_close(struct dm_cache_metadata *cmd)
        kfree(cmd);
 }
 
+/*
+ * Checks that the given cache block is either unmapped or clean.
+ */
+static int block_unmapped_or_clean(struct dm_cache_metadata *cmd, dm_cblock_t b,
+                                  bool *result)
+{
+       int r;
+       __le64 value;
+       dm_oblock_t ob;
+       unsigned flags;
+
+       r = dm_array_get_value(&cmd->info, cmd->root, from_cblock(b), &value);
+       if (r) {
+               DMERR("block_unmapped_or_clean failed");
+               return r;
+       }
+
+       unpack_value(value, &ob, &flags);
+       *result = !((flags & M_VALID) && (flags & M_DIRTY));
+
+       return 0;
+}
+
+static int blocks_are_unmapped_or_clean(struct dm_cache_metadata *cmd,
+                                       dm_cblock_t begin, dm_cblock_t end,
+                                       bool *result)
+{
+       int r;
+       *result = true;
+
+       while (begin != end) {
+               r = block_unmapped_or_clean(cmd, begin, result);
+               if (r)
+                       return r;
+
+               if (!*result) {
+                       DMERR("cache block %llu is dirty",
+                             (unsigned long long) from_cblock(begin));
+                       return 0;
+               }
+
+               begin = to_cblock(from_cblock(begin) + 1);
+       }
+
+       return 0;
+}
+
 int dm_cache_resize(struct dm_cache_metadata *cmd, dm_cblock_t new_cache_size)
 {
        int r;
+       bool clean;
        __le64 null_mapping = pack_value(0, 0);
 
        down_write(&cmd->root_lock);
        __dm_bless_for_disk(&null_mapping);
+
+       if (from_cblock(new_cache_size) < from_cblock(cmd->cache_blocks)) {
+               r = blocks_are_unmapped_or_clean(cmd, new_cache_size, cmd->cache_blocks, &clean);
+               if (r) {
+                       __dm_unbless_for_disk(&null_mapping);
+                       goto out;
+               }
+
+               if (!clean) {
+                       DMERR("unable to shrink cache due to dirty blocks");
+                       r = -EINVAL;
+                       __dm_unbless_for_disk(&null_mapping);
+                       goto out;
+               }
+       }
+
        r = dm_array_resize(&cmd->info, cmd->root, from_cblock(cmd->cache_blocks),
                            from_cblock(new_cache_size),
                            &null_mapping, &cmd->root);
        if (!r)
                cmd->cache_blocks = new_cache_size;
        cmd->changed = true;
+
+out:
        up_write(&cmd->root_lock);
 
        return r;

diff --git a/drivers/md/dm-cache-target.c b/drivers/md/dm-cache-target.c
index 655994fdf3084b63826f7d0687e0f075c7ff6f59..183dfc9db297f58739990dc64459c1e329e97b56 100644 (file)
--- a/drivers/md/dm-cache-target.c
+++ b/drivers/md/dm-cache-target.c
@@ -2502,26 +2502,71 @@ static int load_discard(void *context, sector_t discard_block_size,
        return 0;
 }
 
+static dm_cblock_t get_cache_dev_size(struct cache *cache)
+{
+       sector_t size = get_dev_size(cache->cache_dev);
+       (void) sector_div(size, cache->sectors_per_block);
+       return to_cblock(size);
+}
+
+static bool can_resize(struct cache *cache, dm_cblock_t new_size)
+{
+       if (from_cblock(new_size) > from_cblock(cache->cache_size))
+               return true;
+
+       /*
+        * We can't drop a dirty block when shrinking the cache.
+        */
+       while (from_cblock(new_size) < from_cblock(cache->cache_size)) {
+               new_size = to_cblock(from_cblock(new_size) + 1);
+               if (is_dirty(cache, new_size)) {
+                       DMERR("unable to shrink cache; cache block %llu is dirty",
+                             (unsigned long long) from_cblock(new_size));
+                       return false;
+               }
+       }
+
+       return true;
+}
+
+static int resize_cache_dev(struct cache *cache, dm_cblock_t new_size)
+{
+       int r;
+
+       r = dm_cache_resize(cache->cmd, cache->cache_size);
+       if (r) {
+               DMERR("could not resize cache metadata");
+               return r;
+       }
+
+       cache->cache_size = new_size;
+
+       return 0;
+}
+
 static int cache_preresume(struct dm_target *ti)
 {
        int r = 0;
        struct cache *cache = ti->private;
-       sector_t actual_cache_size = get_dev_size(cache->cache_dev);
-       (void) sector_div(actual_cache_size, cache->sectors_per_block);
+       dm_cblock_t csize = get_cache_dev_size(cache);
 
        /*
         * Check to see if the cache has resized.
         */
-       if (from_cblock(cache->cache_size) != actual_cache_size || !cache->sized) {
-               cache->cache_size = to_cblock(actual_cache_size);
-
-               r = dm_cache_resize(cache->cmd, cache->cache_size);
-               if (r) {
-                       DMERR("could not resize cache metadata");
+       if (!cache->sized) {
+               r = resize_cache_dev(cache, csize);
+               if (r)
                        return r;
-               }
 
                cache->sized = true;
+
+       } else if (csize != cache->cache_size) {
+               if (!can_resize(cache, csize))
+                       return -EINVAL;
+
+               r = resize_cache_dev(cache, csize);
+               if (r)
+                       return r;
        }
 
        if (!cache->loaded_mappings) {