diff options
Diffstat (limited to 'drivers/md/dm-cache-policy.h')
| -rw-r--r-- | drivers/md/dm-cache-policy.h | 187 |
1 files changed, 54 insertions, 133 deletions
diff --git a/drivers/md/dm-cache-policy.h b/drivers/md/dm-cache-policy.h index aa10b1493f34..c05fc3436cef 100644 --- a/drivers/md/dm-cache-policy.h +++ b/drivers/md/dm-cache-policy.h @@ -13,183 +13,100 @@ /*----------------------------------------------------------------*/ -/* FIXME: make it clear which methods are optional. Get debug policy to - * double check this at start. - */ - /* * The cache policy makes the important decisions about which blocks get to * live on the faster cache device. - * - * When the core target has to remap a bio it calls the 'map' method of the - * policy. This returns an instruction telling the core target what to do. - * - * POLICY_HIT: - * That block is in the cache. Remap to the cache and carry on. - * - * POLICY_MISS: - * This block is on the origin device. Remap and carry on. - * - * POLICY_NEW: - * This block is currently on the origin device, but the policy wants to - * move it. The core should: - * - * - hold any further io to this origin block - * - copy the origin to the given cache block - * - release all the held blocks - * - remap the original block to the cache - * - * POLICY_REPLACE: - * This block is currently on the origin device. The policy wants to - * move it to the cache, with the added complication that the destination - * cache block needs a writeback first. The core should: - * - * - hold any further io to this origin block - * - hold any further io to the origin block that's being written back - * - writeback - * - copy new block to cache - * - release held blocks - * - remap bio to cache and reissue. - * - * Should the core run into trouble while processing a POLICY_NEW or - * POLICY_REPLACE instruction it will roll back the policies mapping using - * remove_mapping() or force_mapping(). These methods must not fail. This - * approach avoids having transactional semantics in the policy (ie, the - * core informing the policy when a migration is complete), and hence makes - * it easier to write new policies. - * - * In general policy methods should never block, except in the case of the - * map function when can_migrate is set. So be careful to implement using - * bounded, preallocated memory. */ enum policy_operation { - POLICY_HIT, - POLICY_MISS, - POLICY_NEW, - POLICY_REPLACE -}; - -/* - * When issuing a POLICY_REPLACE the policy needs to make a callback to - * lock the block being demoted. This doesn't need to occur during a - * writeback operation since the block remains in the cache. - */ -struct policy_locker; -typedef int (*policy_lock_fn)(struct policy_locker *l, dm_oblock_t oblock); - -struct policy_locker { - policy_lock_fn fn; + POLICY_PROMOTE, + POLICY_DEMOTE, + POLICY_WRITEBACK }; /* * This is the instruction passed back to the core target. */ -struct policy_result { +struct policy_work { enum policy_operation op; - dm_oblock_t old_oblock; /* POLICY_REPLACE */ - dm_cblock_t cblock; /* POLICY_HIT, POLICY_NEW, POLICY_REPLACE */ + dm_oblock_t oblock; + dm_cblock_t cblock; }; /* - * The cache policy object. Just a bunch of methods. It is envisaged that - * this structure will be embedded in a bigger, policy specific structure - * (ie. use container_of()). + * The cache policy object. It is envisaged that this structure will be + * embedded in a bigger, policy specific structure (ie. use container_of()). */ struct dm_cache_policy { - - /* - * FIXME: make it clear which methods are optional, and which may - * block. - */ - /* * Destroys this object. */ void (*destroy)(struct dm_cache_policy *p); /* - * See large comment above. - * - * oblock - the origin block we're interested in. - * - * can_block - indicates whether the current thread is allowed to - * block. -EWOULDBLOCK returned if it can't and would. - * - * can_migrate - gives permission for POLICY_NEW or POLICY_REPLACE - * instructions. If denied and the policy would have - * returned one of these instructions it should - * return -EWOULDBLOCK. + * Find the location of a block. * - * discarded_oblock - indicates whether the whole origin block is - * in a discarded state (FIXME: better to tell the - * policy about this sooner, so it can recycle that - * cache block if it wants.) - * bio - the bio that triggered this call. - * result - gets filled in with the instruction. + * Must not block. * - * May only return 0, or -EWOULDBLOCK (if !can_migrate) + * Returns 0 if in cache (cblock will be set), -ENOENT if not, < 0 for + * other errors (-EWOULDBLOCK would be typical). data_dir should be + * READ or WRITE. fast_copy should be set if migrating this block would + * be 'cheap' somehow (eg, discarded data). background_queued will be set + * if a migration has just been queued. */ - int (*map)(struct dm_cache_policy *p, dm_oblock_t oblock, - bool can_block, bool can_migrate, bool discarded_oblock, - struct bio *bio, struct policy_locker *locker, - struct policy_result *result); + int (*lookup)(struct dm_cache_policy *p, dm_oblock_t oblock, dm_cblock_t *cblock, + int data_dir, bool fast_copy, bool *background_queued); /* - * Sometimes we want to see if a block is in the cache, without - * triggering any update of stats. (ie. it's not a real hit). - * - * Must not block. + * Sometimes the core target can optimise a migration, eg, the + * block may be discarded, or the bio may cover an entire block. + * In order to optimise it needs the migration immediately though + * so it knows to do something different with the bio. * - * Returns 0 if in cache, -ENOENT if not, < 0 for other errors - * (-EWOULDBLOCK would be typical). + * This method is optional (policy-internal will fallback to using + * lookup). */ - int (*lookup)(struct dm_cache_policy *p, dm_oblock_t oblock, dm_cblock_t *cblock); - - void (*set_dirty)(struct dm_cache_policy *p, dm_oblock_t oblock); - void (*clear_dirty)(struct dm_cache_policy *p, dm_oblock_t oblock); + int (*lookup_with_work)(struct dm_cache_policy *p, + dm_oblock_t oblock, dm_cblock_t *cblock, + int data_dir, bool fast_copy, + struct policy_work **work); /* - * Called when a cache target is first created. Used to load a - * mapping from the metadata device into the policy. + * Retrieves background work. Returns -ENODATA when there's no + * background work. */ - int (*load_mapping)(struct dm_cache_policy *p, dm_oblock_t oblock, - dm_cblock_t cblock, uint32_t hint, bool hint_valid); + int (*get_background_work)(struct dm_cache_policy *p, bool idle, + struct policy_work **result); /* - * Gets the hint for a given cblock. Called in a single threaded - * context. So no locking required. + * You must pass in the same work pointer that you were given, not + * a copy. */ - uint32_t (*get_hint)(struct dm_cache_policy *p, dm_cblock_t cblock); + void (*complete_background_work)(struct dm_cache_policy *p, + struct policy_work *work, + bool success); + + void (*set_dirty)(struct dm_cache_policy *p, dm_cblock_t cblock); + void (*clear_dirty)(struct dm_cache_policy *p, dm_cblock_t cblock); /* - * Override functions used on the error paths of the core target. - * They must succeed. + * Called when a cache target is first created. Used to load a + * mapping from the metadata device into the policy. */ - void (*remove_mapping)(struct dm_cache_policy *p, dm_oblock_t oblock); - void (*force_mapping)(struct dm_cache_policy *p, dm_oblock_t current_oblock, - dm_oblock_t new_oblock); + int (*load_mapping)(struct dm_cache_policy *p, dm_oblock_t oblock, + dm_cblock_t cblock, bool dirty, + uint32_t hint, bool hint_valid); /* - * This is called via the invalidate_cblocks message. It is - * possible the particular cblock has already been removed due to a - * write io in passthrough mode. In which case this should return - * -ENODATA. + * Drops the mapping, irrespective of whether it's clean or dirty. + * Returns -ENODATA if cblock is not mapped. */ - int (*remove_cblock)(struct dm_cache_policy *p, dm_cblock_t cblock); + int (*invalidate_mapping)(struct dm_cache_policy *p, dm_cblock_t cblock); /* - * Provide a dirty block to be written back by the core target. If - * critical_only is set then the policy should only provide work if - * it urgently needs it. - * - * Returns: - * - * 0 and @cblock,@oblock: block to write back provided - * - * -ENODATA: no dirty blocks available + * Gets the hint for a given cblock. Called in a single threaded + * context. So no locking required. */ - int (*writeback_work)(struct dm_cache_policy *p, dm_oblock_t *oblock, dm_cblock_t *cblock, - bool critical_only); + uint32_t (*get_hint)(struct dm_cache_policy *p, dm_cblock_t cblock); /* * How full is the cache? @@ -202,6 +119,8 @@ struct dm_cache_policy { * queue merging has occurred). To stop the policy being fooled by * these, the core target sends regular tick() calls to the policy. * The policy should only count an entry as hit once per tick. + * + * This method is optional. */ void (*tick)(struct dm_cache_policy *p, bool can_block); @@ -213,6 +132,8 @@ struct dm_cache_policy { int (*set_config_value)(struct dm_cache_policy *p, const char *key, const char *value); + void (*allow_migrations)(struct dm_cache_policy *p, bool allow); + /* * Book keeping ptr for the policy register, not for general use. */ |