diff options
| -rw-r--r-- | Documentation/admin-guide/mm/zswap.rst | 10 | ||||
| -rw-r--r-- | include/linux/mmzone.h | 2 | ||||
| -rw-r--r-- | include/linux/zswap.h | 25 | ||||
| -rw-r--r-- | mm/Kconfig | 14 | ||||
| -rw-r--r-- | mm/mmzone.c | 1 | ||||
| -rw-r--r-- | mm/swap_state.c | 2 | ||||
| -rw-r--r-- | mm/zswap.c | 192 |
7 files changed, 240 insertions, 6 deletions
diff --git a/Documentation/admin-guide/mm/zswap.rst b/Documentation/admin-guide/mm/zswap.rst index 45b98390e938..62fc244ec702 100644 --- a/Documentation/admin-guide/mm/zswap.rst +++ b/Documentation/admin-guide/mm/zswap.rst @@ -153,6 +153,16 @@ attribute, e. g.:: Setting this parameter to 100 will disable the hysteresis. +When there is a sizable amount of cold memory residing in the zswap pool, it +can be advantageous to proactively write these cold pages to swap and reclaim +the memory for other use cases. By default, the zswap shrinker is disabled. +User can enable it as follows: + + echo Y > /sys/module/zswap/parameters/shrinker_enabled + +This can be enabled at the boot time if ``CONFIG_ZSWAP_SHRINKER_DEFAULT_ON`` is +selected. + A debugfs interface is provided for various statistic about pool size, number of pages stored, same-value filled pages and various counters for the reasons pages are rejected. diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h index 14faffa4354f..9ef9d010bff0 100644 --- a/include/linux/mmzone.h +++ b/include/linux/mmzone.h @@ -22,6 +22,7 @@ #include <linux/mm_types.h> #include <linux/page-flags.h> #include <linux/local_lock.h> +#include <linux/zswap.h> #include <asm/page.h> /* Free memory management - zoned buddy allocator. */ @@ -641,6 +642,7 @@ struct lruvec { #ifdef CONFIG_MEMCG struct pglist_data *pgdat; #endif + struct zswap_lruvec_state zswap_lruvec_state; }; /* Isolate for asynchronous migration */ diff --git a/include/linux/zswap.h b/include/linux/zswap.h index e571e393669b..08c240e16a01 100644 --- a/include/linux/zswap.h +++ b/include/linux/zswap.h @@ -5,20 +5,40 @@ #include <linux/types.h> #include <linux/mm_types.h> +struct lruvec; + extern u64 zswap_pool_total_size; extern atomic_t zswap_stored_pages; #ifdef CONFIG_ZSWAP +struct zswap_lruvec_state { + /* + * Number of pages in zswap that should be protected from the shrinker. + * This number is an estimate of the following counts: + * + * a) Recent page faults. + * b) Recent insertion to the zswap LRU. This includes new zswap stores, + * as well as recent zswap LRU rotations. + * + * These pages are likely to be warm, and might incur IO if the are written + * to swap. + */ + atomic_long_t nr_zswap_protected; +}; + bool zswap_store(struct folio *folio); bool zswap_load(struct folio *folio); void zswap_invalidate(int type, pgoff_t offset); void zswap_swapon(int type); void zswap_swapoff(int type); void zswap_memcg_offline_cleanup(struct mem_cgroup *memcg); - +void zswap_lruvec_state_init(struct lruvec *lruvec); +void zswap_page_swapin(struct page *page); #else +struct zswap_lruvec_state {}; + static inline bool zswap_store(struct folio *folio) { return false; @@ -33,7 +53,8 @@ static inline void zswap_invalidate(int type, pgoff_t offset) {} static inline void zswap_swapon(int type) {} static inline void zswap_swapoff(int type) {} static inline void zswap_memcg_offline_cleanup(struct mem_cgroup *memcg) {} - +static inline void zswap_lruvec_state_init(struct lruvec *lruvec) {} +static inline void zswap_page_swapin(struct page *page) {} #endif #endif /* _LINUX_ZSWAP_H */ diff --git a/mm/Kconfig b/mm/Kconfig index 57cd378c73d6..ca87cdb72f11 100644 --- a/mm/Kconfig +++ b/mm/Kconfig @@ -61,6 +61,20 @@ config ZSWAP_EXCLUSIVE_LOADS_DEFAULT_ON The cost is that if the page was never dirtied and needs to be swapped out again, it will be re-compressed. +config ZSWAP_SHRINKER_DEFAULT_ON + bool "Shrink the zswap pool on memory pressure" + depends on ZSWAP + default n + help + If selected, the zswap shrinker will be enabled, and the pages + stored in the zswap pool will become available for reclaim (i.e + written back to the backing swap device) on memory pressure. + + This means that zswap writeback could happen even if the pool is + not yet full, or the cgroup zswap limit has not been reached, + reducing the chance that cold pages will reside in the zswap pool + and consume memory indefinitely. + choice prompt "Default compressor" depends on ZSWAP diff --git a/mm/mmzone.c b/mm/mmzone.c index b594d3f268fe..c01896eca736 100644 --- a/mm/mmzone.c +++ b/mm/mmzone.c @@ -78,6 +78,7 @@ void lruvec_init(struct lruvec *lruvec) memset(lruvec, 0, sizeof(struct lruvec)); spin_lock_init(&lruvec->lru_lock); + zswap_lruvec_state_init(lruvec); for_each_lru(lru) INIT_LIST_HEAD(&lruvec->lists[lru]); diff --git a/mm/swap_state.c b/mm/swap_state.c index 6c84236382f3..c597cec606e4 100644 --- a/mm/swap_state.c +++ b/mm/swap_state.c @@ -687,6 +687,7 @@ skip: &page_allocated, false); if (unlikely(page_allocated)) swap_readpage(page, false, NULL); + zswap_page_swapin(page); return page; } @@ -862,6 +863,7 @@ skip: &page_allocated, false); if (unlikely(page_allocated)) swap_readpage(page, false, NULL); + zswap_page_swapin(page); return page; } diff --git a/mm/zswap.c b/mm/zswap.c index c329fca810c8..015425ed9003 100644 --- a/mm/zswap.c +++ b/mm/zswap.c @@ -148,6 +148,11 @@ module_param_named(exclusive_loads, zswap_exclusive_loads_enabled, bool, 0644); /* Number of zpools in zswap_pool (empirically determined for scalability) */ #define ZSWAP_NR_ZPOOLS 32 +/* Enable/disable memory pressure-based shrinker. */ +static bool zswap_shrinker_enabled = IS_ENABLED( + CONFIG_ZSWAP_SHRINKER_DEFAULT_ON); +module_param_named(shrinker_enabled, zswap_shrinker_enabled, bool, 0644); + /********************************* * data structures **********************************/ @@ -177,6 +182,8 @@ struct zswap_pool { char tfm_name[CRYPTO_MAX_ALG_NAME]; struct list_lru list_lru; struct mem_cgroup *next_shrink; + struct shrinker *shrinker; + atomic_t nr_stored; }; /* @@ -275,17 +282,26 @@ static bool zswap_can_accept(void) DIV_ROUND_UP(zswap_pool_total_size, PAGE_SIZE); } +static u64 get_zswap_pool_size(struct zswap_pool *pool) +{ + u64 pool_size = 0; + int i; + + for (i = 0; i < ZSWAP_NR_ZPOOLS; i++) + pool_size += zpool_get_total_size(pool->zpools[i]); + + return pool_size; +} + static void zswap_update_total_size(void) { struct zswap_pool *pool; u64 total = 0; - int i; rcu_read_lock(); list_for_each_entry_rcu(pool, &zswap_pools, list) - for (i = 0; i < ZSWAP_NR_ZPOOLS; i++) - total += zpool_get_total_size(pool->zpools[i]); + total += get_zswap_pool_size(pool); rcu_read_unlock(); @@ -345,12 +361,33 @@ static void zswap_entry_cache_free(struct zswap_entry *entry) } /********************************* +* zswap lruvec functions +**********************************/ +void zswap_lruvec_state_init(struct lruvec *lruvec) +{ + atomic_long_set(&lruvec->zswap_lruvec_state.nr_zswap_protected, 0); +} + +void zswap_page_swapin(struct page *page) +{ + struct lruvec *lruvec; + + if (page) { + lruvec = folio_lruvec(page_folio(page)); + atomic_long_inc(&lruvec->zswap_lruvec_state.nr_zswap_protected); + } +} + +/********************************* * lru functions **********************************/ static void zswap_lru_add(struct list_lru *list_lru, struct zswap_entry *entry) { + atomic_long_t *nr_zswap_protected; + unsigned long lru_size, old, new; int nid = entry_to_nid(entry); struct mem_cgroup *memcg; + struct lruvec *lruvec; /* * Note that it is safe to use rcu_read_lock() here, even in the face of @@ -368,6 +405,19 @@ static void zswap_lru_add(struct list_lru *list_lru, struct zswap_entry *entry) memcg = mem_cgroup_from_entry(entry); /* will always succeed */ list_lru_add(list_lru, &entry->lru, nid, memcg); + + /* Update the protection area */ + lru_size = list_lru_count_one(list_lru, nid, memcg); + lruvec = mem_cgroup_lruvec(memcg, NODE_DATA(nid)); + nr_zswap_protected = &lruvec->zswap_lruvec_state.nr_zswap_protected; + old = atomic_long_inc_return(nr_zswap_protected); + /* + * Decay to avoid overflow and adapt to changing workloads. + * This is based on LRU reclaim cost decaying heuristics. + */ + do { + new = old > lru_size / 4 ? old / 2 : old; + } while (!atomic_long_try_cmpxchg(nr_zswap_protected, &old, new)); rcu_read_unlock(); } @@ -389,6 +439,7 @@ static void zswap_lru_putback(struct list_lru *list_lru, int nid = entry_to_nid(entry); spinlock_t *lock = &list_lru->node[nid].lock; struct mem_cgroup *memcg; + struct lruvec *lruvec; rcu_read_lock(); memcg = mem_cgroup_from_entry(entry); @@ -396,6 +447,10 @@ static void zswap_lru_putback(struct list_lru *list_lru, /* we cannot use list_lru_add here, because it increments node's lru count */ list_lru_putback(list_lru, &entry->lru, nid, memcg); spin_unlock(lock); + + lruvec = mem_cgroup_lruvec(memcg, NODE_DATA(entry_to_nid(entry))); + /* increment the protection area to account for the LRU rotation. */ + atomic_long_inc(&lruvec->zswap_lruvec_state.nr_zswap_protected); rcu_read_unlock(); } @@ -485,6 +540,7 @@ static void zswap_free_entry(struct zswap_entry *entry) else { zswap_lru_del(&entry->pool->list_lru, entry); zpool_free(zswap_find_zpool(entry), entry->handle); + atomic_dec(&entry->pool->nr_stored); zswap_pool_put(entry->pool); } zswap_entry_cache_free(entry); @@ -527,6 +583,109 @@ static struct zswap_entry *zswap_entry_find_get(struct rb_root *root, } /********************************* +* shrinker functions +**********************************/ +static enum lru_status shrink_memcg_cb(struct list_head *item, struct list_lru_one *l, + spinlock_t *lock, void *arg); + +static unsigned long zswap_shrinker_scan(struct shrinker *shrinker, + struct shrink_control *sc) +{ + struct lruvec *lruvec = mem_cgroup_lruvec(sc->memcg, NODE_DATA(sc->nid)); + unsigned long shrink_ret, nr_protected, lru_size; + struct zswap_pool *pool = shrinker->private_data; + bool encountered_page_in_swapcache = false; + + if (!zswap_shrinker_enabled) { + sc->nr_scanned = 0; + return SHRINK_STOP; + } + + nr_protected = + atomic_long_read(&lruvec->zswap_lruvec_state.nr_zswap_protected); + lru_size = list_lru_shrink_count(&pool->list_lru, sc); + + /* + * Abort if we are shrinking into the protected region. + * + * This short-circuiting is necessary because if we have too many multiple + * concurrent reclaimers getting the freeable zswap object counts at the + * same time (before any of them made reasonable progress), the total + * number of reclaimed objects might be more than the number of unprotected + * objects (i.e the reclaimers will reclaim into the protected area of the + * zswap LRU). + */ + if (nr_protected >= lru_size - sc->nr_to_scan) { + sc->nr_scanned = 0; + return SHRINK_STOP; + } + + shrink_ret = list_lru_shrink_walk(&pool->list_lru, sc, &shrink_memcg_cb, + &encountered_page_in_swapcache); + + if (encountered_page_in_swapcache) + return SHRINK_STOP; + + return shrink_ret ? shrink_ret : SHRINK_STOP; +} + +static unsigned long zswap_shrinker_count(struct shrinker *shrinker, + struct shrink_control *sc) +{ + struct zswap_pool *pool = shrinker->private_data; + struct mem_cgroup *memcg = sc->memcg; + struct lruvec *lruvec = mem_cgroup_lruvec(memcg, NODE_DATA(sc->nid)); + unsigned long nr_backing, nr_stored, nr_freeable, nr_protected; + + if (!zswap_shrinker_enabled) + return 0; + +#ifdef CONFIG_MEMCG_KMEM + mem_cgroup_flush_stats(); + nr_backing = memcg_page_state(memcg, MEMCG_ZSWAP_B) >> PAGE_SHIFT; + nr_stored = memcg_page_state(memcg, MEMCG_ZSWAPPED); +#else + /* use pool stats instead of memcg stats */ + nr_backing = get_zswap_pool_size(pool) >> PAGE_SHIFT; + nr_stored = atomic_read(&pool->nr_stored); +#endif + + if (!nr_stored) + return 0; + + nr_protected = + atomic_long_read(&lruvec->zswap_lruvec_state.nr_zswap_protected); + nr_freeable = list_lru_shrink_count(&pool->list_lru, sc); + /* + * Subtract the lru size by an estimate of the number of pages + * that should be protected. + */ + nr_freeable = nr_freeable > nr_protected ? nr_freeable - nr_protected : 0; + + /* + * Scale the number of freeable pages by the memory saving factor. + * This ensures that the better zswap compresses memory, the fewer + * pages we will evict to swap (as it will otherwise incur IO for + * relatively small memory saving). + */ + return mult_frac(nr_freeable, nr_backing, nr_stored); +} + +static void zswap_alloc_shrinker(struct zswap_pool *pool) +{ + pool->shrinker = + shrinker_alloc(SHRINKER_NUMA_AWARE | SHRINKER_MEMCG_AWARE, "mm-zswap"); + if (!pool->shrinker) + return; + + pool->shrinker->private_data = pool; + pool->shrinker->scan_objects = zswap_shrinker_scan; + pool->shrinker->count_objects = zswap_shrinker_count; + pool->shrinker->batch = 0; + pool->shrinker->seeks = DEFAULT_SEEKS; +} + +/********************************* * per-cpu code **********************************/ static DEFINE_PER_CPU(u8 *, zswap_dstmem); @@ -721,6 +880,7 @@ static enum lru_status shrink_memcg_cb(struct list_head *item, struct list_lru_o spinlock_t *lock, void *arg) { struct zswap_entry *entry = container_of(item, struct zswap_entry, lru); + bool *encountered_page_in_swapcache = (bool *)arg; struct zswap_tree *tree; pgoff_t swpoffset; enum lru_status ret = LRU_REMOVED_RETRY; @@ -756,6 +916,17 @@ static enum lru_status shrink_memcg_cb(struct list_head *item, struct list_lru_o zswap_reject_reclaim_fail++; zswap_lru_putback(&entry->pool->list_lru, entry); ret = LRU_RETRY; + + /* + * Encountering a page already in swap cache is a sign that we are shrinking + * into the warmer region. We should terminate shrinking (if we're in the dynamic + * shrinker context). + */ + if (writeback_result == -EEXIST && encountered_page_in_swapcache) { + ret = LRU_SKIP; + *encountered_page_in_swapcache = true; + } + goto put_unlock; } zswap_written_back_pages++; @@ -914,6 +1085,11 @@ static struct zswap_pool *zswap_pool_create(char *type, char *compressor) &pool->node); if (ret) goto error; + + zswap_alloc_shrinker(pool); + if (!pool->shrinker) + goto error; + pr_debug("using %s compressor\n", pool->tfm_name); /* being the current pool takes 1 ref; this func expects the @@ -921,13 +1097,19 @@ static struct zswap_pool *zswap_pool_create(char *type, char *compressor) */ kref_init(&pool->kref); INIT_LIST_HEAD(&pool->list); - list_lru_init_memcg(&pool->list_lru, NULL); + if (list_lru_init_memcg(&pool->list_lru, pool->shrinker)) + goto lru_fail; + shrinker_register(pool->shrinker); INIT_WORK(&pool->shrink_work, shrink_worker); + atomic_set(&pool->nr_stored, 0); zswap_pool_debug("created", pool); return pool; +lru_fail: + list_lru_destroy(&pool->list_lru); + shrinker_free(pool->shrinker); error: if (pool->acomp_ctx) free_percpu(pool->acomp_ctx); @@ -985,6 +1167,7 @@ static void zswap_pool_destroy(struct zswap_pool *pool) zswap_pool_debug("destroying", pool); + shrinker_free(pool->shrinker); cpuhp_state_remove_instance(CPUHP_MM_ZSWP_POOL_PREPARE, &pool->node); free_percpu(pool->acomp_ctx); list_lru_destroy(&pool->list_lru); @@ -1536,6 +1719,7 @@ insert_entry: if (entry->length) { INIT_LIST_HEAD(&entry->lru); zswap_lru_add(&entry->pool->list_lru, entry); + atomic_inc(&entry->pool->nr_stored); } spin_unlock(&tree->lock); |