From 791188065be0d3715e6696412ab9c7a5f6b52bd3 Mon Sep 17 00:00:00 2001 From: Joe Thornber Date: Fri, 24 Mar 2023 23:01:03 -0400 Subject: [PATCH] dm bufio: add lock_history optimization for cache iterators Sometimes it is beneficial to repeatedly get and drop locks as part of an iteration. Introduce lock_history struct to help avoid redundant drop and gets of the same lock. Optimizes cache_iterate, cache_mark_many and cache_evict. Signed-off-by: Joe Thornber Signed-off-by: Mike Snitzer --- drivers/md/dm-bufio.c | 119 +++++++++++++++++++++++++++++++++++++++--- 1 file changed, 111 insertions(+), 8 deletions(-) diff --git a/drivers/md/dm-bufio.c b/drivers/md/dm-bufio.c index 1e000ec73bd693..9ac50024006dd1 100644 --- a/drivers/md/dm-bufio.c +++ b/drivers/md/dm-bufio.c @@ -421,6 +421,70 @@ static inline void cache_write_unlock(struct dm_buffer_cache *bc, sector_t block up_write(&bc->trees[cache_index(block)].lock); } +/* + * Sometimes we want to repeatedly get and drop locks as part of an iteration. + * This struct helps avoid redundant drop and gets of the same lock. + */ +struct lock_history { + struct dm_buffer_cache *cache; + bool write; + unsigned int previous; +}; + +static void lh_init(struct lock_history *lh, struct dm_buffer_cache *cache, bool write) +{ + lh->cache = cache; + lh->write = write; + lh->previous = NR_LOCKS; /* indicates no previous */ +} + +static void __lh_lock(struct lock_history *lh, unsigned int index) +{ + if (lh->write) + down_write(&lh->cache->trees[index].lock); + else + down_read(&lh->cache->trees[index].lock); +} + +static void __lh_unlock(struct lock_history *lh, unsigned int index) +{ + if (lh->write) + up_write(&lh->cache->trees[index].lock); + else + up_read(&lh->cache->trees[index].lock); +} + +/* + * Make sure you call this since it will unlock the final lock. + */ +static void lh_exit(struct lock_history *lh) +{ + if (lh->previous != NR_LOCKS) { + __lh_unlock(lh, lh->previous); + lh->previous = NR_LOCKS; + } +} + +/* + * Named 'next' because there is no corresponding + * 'up/unlock' call since it's done automatically. + */ +static void lh_next(struct lock_history *lh, sector_t b) +{ + unsigned int index = cache_index(b); + + if (lh->previous != NR_LOCKS) { + if (lh->previous != index) { + __lh_unlock(lh, lh->previous); + __lh_lock(lh, index); + lh->previous = index; + } + } else { + __lh_lock(lh, index); + lh->previous = index; + } +} + static inline struct dm_buffer *le_to_buffer(struct lru_entry *le) { return container_of(le, struct dm_buffer, lru); @@ -550,6 +614,7 @@ typedef enum evict_result (*b_predicate)(struct dm_buffer *, void *); * predicate the hold_count of the selected buffer will be zero. */ struct evict_wrapper { + struct lock_history *lh; b_predicate pred; void *context; }; @@ -563,16 +628,19 @@ static enum evict_result __evict_pred(struct lru_entry *le, void *context) struct evict_wrapper *w = context; struct dm_buffer *b = le_to_buffer(le); + lh_next(w->lh, b->block); + if (atomic_read(&b->hold_count)) return ER_DONT_EVICT; return w->pred(b, w->context); } -static struct dm_buffer *cache_evict(struct dm_buffer_cache *bc, int list_mode, - b_predicate pred, void *context) +static struct dm_buffer *__cache_evict(struct dm_buffer_cache *bc, int list_mode, + b_predicate pred, void *context, + struct lock_history *lh) { - struct evict_wrapper w = {.pred = pred, .context = context}; + struct evict_wrapper w = {.lh = lh, .pred = pred, .context = context}; struct lru_entry *le; struct dm_buffer *b; @@ -587,6 +655,19 @@ static struct dm_buffer *cache_evict(struct dm_buffer_cache *bc, int list_mode, return b; } +static struct dm_buffer *cache_evict(struct dm_buffer_cache *bc, int list_mode, + b_predicate pred, void *context) +{ + struct dm_buffer *b; + struct lock_history lh; + + lh_init(&lh, bc, true); + b = __cache_evict(bc, list_mode, pred, context, &lh); + lh_exit(&lh); + + return b; +} + /*--------------*/ /* @@ -609,12 +690,12 @@ static void cache_mark(struct dm_buffer_cache *bc, struct dm_buffer *b, int list * Runs through the lru associated with 'old_mode', if the predicate matches then * it moves them to 'new_mode'. Not threadsafe. */ -static void cache_mark_many(struct dm_buffer_cache *bc, int old_mode, int new_mode, - b_predicate pred, void *context) +static void __cache_mark_many(struct dm_buffer_cache *bc, int old_mode, int new_mode, + b_predicate pred, void *context, struct lock_history *lh) { struct lru_entry *le; struct dm_buffer *b; - struct evict_wrapper w = {.pred = pred, .context = context}; + struct evict_wrapper w = {.lh = lh, .pred = pred, .context = context}; while (true) { le = lru_evict(&bc->lru[old_mode], __evict_pred, &w); @@ -627,6 +708,16 @@ static void cache_mark_many(struct dm_buffer_cache *bc, int old_mode, int new_mo } } +static void cache_mark_many(struct dm_buffer_cache *bc, int old_mode, int new_mode, + b_predicate pred, void *context) +{ + struct lock_history lh; + + lh_init(&lh, bc, true); + __cache_mark_many(bc, old_mode, new_mode, pred, context, &lh); + lh_exit(&lh); +} + /*--------------*/ /* @@ -645,8 +736,8 @@ enum it_action { typedef enum it_action (*iter_fn)(struct dm_buffer *b, void *context); -static void cache_iterate(struct dm_buffer_cache *bc, int list_mode, - iter_fn fn, void *context) +static void __cache_iterate(struct dm_buffer_cache *bc, int list_mode, + iter_fn fn, void *context, struct lock_history *lh) { struct lru *lru = &bc->lru[list_mode]; struct lru_entry *le, *first; @@ -658,6 +749,8 @@ static void cache_iterate(struct dm_buffer_cache *bc, int list_mode, do { struct dm_buffer *b = le_to_buffer(le); + lh_next(lh, b->block); + switch (fn(b, context)) { case IT_NEXT: break; @@ -671,6 +764,16 @@ static void cache_iterate(struct dm_buffer_cache *bc, int list_mode, } while (le != first); } +static void cache_iterate(struct dm_buffer_cache *bc, int list_mode, + iter_fn fn, void *context) +{ + struct lock_history lh; + + lh_init(&lh, bc, false); + __cache_iterate(bc, list_mode, fn, context, &lh); + lh_exit(&lh); +} + /*--------------*/ /*