On Thu, Nov 30, 2023 at 11:40 AM Nhat Pham <nphamcs@xxxxxxxxx> wrote: > > From: Domenico Cerasuolo <cerasuolodomenico@xxxxxxxxx> > > Currently, we only have a single global LRU for zswap. This makes it > impossible to perform worload-specific shrinking - an memcg cannot > determine which pages in the pool it owns, and often ends up writing > pages from other memcgs. This issue has been previously observed in > practice and mitigated by simply disabling memcg-initiated shrinking: > > https://lore.kernel.org/all/20230530232435.3097106-1-nphamcs@xxxxxxxxx/T/#u > > This patch fully resolves the issue by replacing the global zswap LRU > with memcg- and NUMA-specific LRUs, and modify the reclaim logic: > > a) When a store attempt hits an memcg limit, it now triggers a > synchronous reclaim attempt that, if successful, allows the new > hotter page to be accepted by zswap. > b) If the store attempt instead hits the global zswap limit, it will > trigger an asynchronous reclaim attempt, in which an memcg is > selected for reclaim in a round-robin-like fashion. > > Signed-off-by: Domenico Cerasuolo <cerasuolodomenico@xxxxxxxxx> > Co-developed-by: Nhat Pham <nphamcs@xxxxxxxxx> > Signed-off-by: Nhat Pham <nphamcs@xxxxxxxxx> > --- > include/linux/memcontrol.h | 5 + > include/linux/zswap.h | 2 + > mm/memcontrol.c | 2 + > mm/swap.h | 3 +- > mm/swap_state.c | 24 +++- > mm/zswap.c | 269 +++++++++++++++++++++++++++++-------- > 6 files changed, 245 insertions(+), 60 deletions(-) > > diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h > index 2bd7d14ace78..a308c8eacf20 100644 > --- a/include/linux/memcontrol.h > +++ b/include/linux/memcontrol.h > @@ -1192,6 +1192,11 @@ static inline struct mem_cgroup *page_memcg_check(struct page *page) > return NULL; > } > > +static inline struct mem_cgroup *get_mem_cgroup_from_objcg(struct obj_cgroup *objcg) > +{ > + return NULL; > +} > + > static inline bool folio_memcg_kmem(struct folio *folio) > { > return false; > diff --git a/include/linux/zswap.h b/include/linux/zswap.h > index 2a60ce39cfde..e571e393669b 100644 > --- a/include/linux/zswap.h > +++ b/include/linux/zswap.h > @@ -15,6 +15,7 @@ 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); > > #else > > @@ -31,6 +32,7 @@ static inline bool zswap_load(struct folio *folio) > 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) {} > > #endif > > diff --git a/mm/memcontrol.c b/mm/memcontrol.c > index 470821d1ba1a..792ca21c5815 100644 > --- a/mm/memcontrol.c > +++ b/mm/memcontrol.c > @@ -5614,6 +5614,8 @@ static void mem_cgroup_css_offline(struct cgroup_subsys_state *css) > page_counter_set_min(&memcg->memory, 0); > page_counter_set_low(&memcg->memory, 0); > > + zswap_memcg_offline_cleanup(memcg); > + > memcg_offline_kmem(memcg); > reparent_shrinker_deferred(memcg); > wb_memcg_offline(memcg); > diff --git a/mm/swap.h b/mm/swap.h > index 73c332ee4d91..c0dc73e10e91 100644 > --- a/mm/swap.h > +++ b/mm/swap.h > @@ -51,7 +51,8 @@ struct page *read_swap_cache_async(swp_entry_t entry, gfp_t gfp_mask, > struct swap_iocb **plug); > struct page *__read_swap_cache_async(swp_entry_t entry, gfp_t gfp_mask, > struct mempolicy *mpol, pgoff_t ilx, > - bool *new_page_allocated); > + bool *new_page_allocated, > + bool skip_if_exists); > struct page *swap_cluster_readahead(swp_entry_t entry, gfp_t flag, > struct mempolicy *mpol, pgoff_t ilx); > struct page *swapin_readahead(swp_entry_t entry, gfp_t flag, > diff --git a/mm/swap_state.c b/mm/swap_state.c > index 85d9e5806a6a..6c84236382f3 100644 > --- a/mm/swap_state.c > +++ b/mm/swap_state.c > @@ -412,7 +412,8 @@ struct folio *filemap_get_incore_folio(struct address_space *mapping, > > struct page *__read_swap_cache_async(swp_entry_t entry, gfp_t gfp_mask, > struct mempolicy *mpol, pgoff_t ilx, > - bool *new_page_allocated) > + bool *new_page_allocated, > + bool skip_if_exists) > { > struct swap_info_struct *si; > struct folio *folio; > @@ -470,6 +471,17 @@ struct page *__read_swap_cache_async(swp_entry_t entry, gfp_t gfp_mask, > if (err != -EEXIST) > goto fail_put_swap; > > + /* > + * Protect against a recursive call to __read_swap_cache_async() > + * on the same entry waiting forever here because SWAP_HAS_CACHE > + * is set but the folio is not the swap cache yet. This can > + * happen today if mem_cgroup_swapin_charge_folio() below > + * triggers reclaim through zswap, which may call > + * __read_swap_cache_async() in the writeback path. > + */ > + if (skip_if_exists) > + goto fail_put_swap; > + > /* > * We might race against __delete_from_swap_cache(), and > * stumble across a swap_map entry whose SWAP_HAS_CACHE > @@ -537,7 +549,7 @@ struct page *read_swap_cache_async(swp_entry_t entry, gfp_t gfp_mask, > > mpol = get_vma_policy(vma, addr, 0, &ilx); > page = __read_swap_cache_async(entry, gfp_mask, mpol, ilx, > - &page_allocated); > + &page_allocated, false); > mpol_cond_put(mpol); > > if (page_allocated) > @@ -654,7 +666,7 @@ struct page *swap_cluster_readahead(swp_entry_t entry, gfp_t gfp_mask, > /* Ok, do the async read-ahead now */ > page = __read_swap_cache_async( > swp_entry(swp_type(entry), offset), > - gfp_mask, mpol, ilx, &page_allocated); > + gfp_mask, mpol, ilx, &page_allocated, false); > if (!page) > continue; > if (page_allocated) { > @@ -672,7 +684,7 @@ struct page *swap_cluster_readahead(swp_entry_t entry, gfp_t gfp_mask, > skip: > /* The page was likely read above, so no need for plugging here */ > page = __read_swap_cache_async(entry, gfp_mask, mpol, ilx, > - &page_allocated); > + &page_allocated, false); > if (unlikely(page_allocated)) > swap_readpage(page, false, NULL); > return page; > @@ -827,7 +839,7 @@ static struct page *swap_vma_readahead(swp_entry_t targ_entry, gfp_t gfp_mask, > pte_unmap(pte); > pte = NULL; > page = __read_swap_cache_async(entry, gfp_mask, mpol, ilx, > - &page_allocated); > + &page_allocated, false); > if (!page) > continue; > if (page_allocated) { > @@ -847,7 +859,7 @@ static struct page *swap_vma_readahead(swp_entry_t targ_entry, gfp_t gfp_mask, > skip: > /* The page was likely read above, so no need for plugging here */ > page = __read_swap_cache_async(targ_entry, gfp_mask, mpol, targ_ilx, > - &page_allocated); > + &page_allocated, false); > if (unlikely(page_allocated)) > swap_readpage(page, false, NULL); > return page; > diff --git a/mm/zswap.c b/mm/zswap.c > index 4bdb2d83bb0d..f323e45cbdc7 100644 > --- a/mm/zswap.c > +++ b/mm/zswap.c > @@ -35,6 +35,7 @@ > #include <linux/writeback.h> > #include <linux/pagemap.h> > #include <linux/workqueue.h> > +#include <linux/list_lru.h> > > #include "swap.h" > #include "internal.h" > @@ -174,8 +175,8 @@ struct zswap_pool { > struct work_struct shrink_work; > struct hlist_node node; > char tfm_name[CRYPTO_MAX_ALG_NAME]; > - struct list_head lru; > - spinlock_t lru_lock; > + struct list_lru list_lru; > + struct mem_cgroup *next_shrink; > }; > > /* > @@ -291,15 +292,46 @@ static void zswap_update_total_size(void) > zswap_pool_total_size = total; > } > > +/* should be called under RCU */ > +#ifdef CONFIG_MEMCG > +static inline struct mem_cgroup *mem_cgroup_from_entry(struct zswap_entry *entry) > +{ > + return entry->objcg ? obj_cgroup_memcg(entry->objcg) : NULL; > +} > +#else > +static inline struct mem_cgroup *mem_cgroup_from_entry(struct zswap_entry *entry) > +{ > + return NULL; > +} > +#endif > + > +static inline int entry_to_nid(struct zswap_entry *entry) > +{ > + return page_to_nid(virt_to_page(entry)); > +} > + > +void zswap_memcg_offline_cleanup(struct mem_cgroup *memcg) > +{ > + struct zswap_pool *pool; > + > + /* lock out zswap pools list modification */ > + spin_lock(&zswap_pools_lock); > + list_for_each_entry(pool, &zswap_pools, list) { > + if (pool->next_shrink == memcg) > + pool->next_shrink = mem_cgroup_iter(NULL, pool->next_shrink, NULL); > + } > + spin_unlock(&zswap_pools_lock); > +} > + > /********************************* > * zswap entry functions > **********************************/ > static struct kmem_cache *zswap_entry_cache; > > -static struct zswap_entry *zswap_entry_cache_alloc(gfp_t gfp) > +static struct zswap_entry *zswap_entry_cache_alloc(gfp_t gfp, int nid) > { > struct zswap_entry *entry; > - entry = kmem_cache_alloc(zswap_entry_cache, gfp); > + entry = kmem_cache_alloc_node(zswap_entry_cache, gfp, nid); > if (!entry) > return NULL; > entry->refcount = 1; > @@ -312,6 +344,61 @@ static void zswap_entry_cache_free(struct zswap_entry *entry) > kmem_cache_free(zswap_entry_cache, entry); > } > > +/********************************* > +* lru functions > +**********************************/ > +static void zswap_lru_add(struct list_lru *list_lru, struct zswap_entry *entry) > +{ > + int nid = entry_to_nid(entry); > + struct mem_cgroup *memcg; > + > + /* > + * Note that it is safe to use rcu_read_lock() here, even in the face of > + * concurrent memcg offlining. Thanks to the memcg->kmemcg_id indirection > + * used in list_lru lookup, only two scenarios are possible: > + * > + * 1. list_lru_add() is called before memcg->kmemcg_id is updated. The > + * new entry will be reparented to memcg's parent's list_lru. > + * 2. list_lru_add() is called after memcg->kmemcg_id is updated. The > + * new entry will be added directly to memcg's parent's list_lru. > + * > + * Similar reasoning holds for list_lru_del() and list_lru_putback(). > + */ > + rcu_read_lock(); > + memcg = mem_cgroup_from_entry(entry); > + /* will always succeed */ > + list_lru_add(list_lru, &entry->lru, nid, memcg); > + rcu_read_unlock(); > +} > + > +static void zswap_lru_del(struct list_lru *list_lru, struct zswap_entry *entry) > +{ > + int nid = entry_to_nid(entry); > + struct mem_cgroup *memcg; > + > + rcu_read_lock(); > + memcg = mem_cgroup_from_entry(entry); > + /* will always succeed */ > + list_lru_del(list_lru, &entry->lru, nid, memcg); > + rcu_read_unlock(); > +} > + > +static void zswap_lru_putback(struct list_lru *list_lru, > + struct zswap_entry *entry) > +{ > + int nid = entry_to_nid(entry); > + spinlock_t *lock = &list_lru->node[nid].lock; > + struct mem_cgroup *memcg; > + > + rcu_read_lock(); > + memcg = mem_cgroup_from_entry(entry); > + spin_lock(lock); > + /* 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); > + rcu_read_unlock(); > +} > + > /********************************* > * rbtree functions > **********************************/ > @@ -396,9 +483,7 @@ static void zswap_free_entry(struct zswap_entry *entry) > if (!entry->length) > atomic_dec(&zswap_same_filled_pages); > else { > - spin_lock(&entry->pool->lru_lock); > - list_del(&entry->lru); > - spin_unlock(&entry->pool->lru_lock); > + zswap_lru_del(&entry->pool->list_lru, entry); > zpool_free(zswap_find_zpool(entry), entry->handle); > zswap_pool_put(entry->pool); > } > @@ -632,21 +717,15 @@ static void zswap_invalidate_entry(struct zswap_tree *tree, > zswap_entry_put(tree, entry); > } > > -static int zswap_reclaim_entry(struct zswap_pool *pool) > +static enum lru_status shrink_memcg_cb(struct list_head *item, struct list_lru_one *l, > + spinlock_t *lock, void *arg) > { > - struct zswap_entry *entry; > + struct zswap_entry *entry = container_of(item, struct zswap_entry, lru); > struct zswap_tree *tree; > pgoff_t swpoffset; > - int ret; > + enum lru_status ret = LRU_REMOVED_RETRY; > + int writeback_result; > > - /* Get an entry off the LRU */ > - spin_lock(&pool->lru_lock); > - if (list_empty(&pool->lru)) { > - spin_unlock(&pool->lru_lock); > - return -EINVAL; > - } > - entry = list_last_entry(&pool->lru, struct zswap_entry, lru); > - list_del_init(&entry->lru); > /* > * Once the lru lock is dropped, the entry might get freed. The > * swpoffset is copied to the stack, and entry isn't deref'd again > @@ -654,28 +733,32 @@ static int zswap_reclaim_entry(struct zswap_pool *pool) > */ > swpoffset = swp_offset(entry->swpentry); > tree = zswap_trees[swp_type(entry->swpentry)]; > - spin_unlock(&pool->lru_lock); > + list_lru_isolate(l, item); > + /* > + * It's safe to drop the lock here because we return either > + * LRU_REMOVED_RETRY or LRU_RETRY. > + */ > + spin_unlock(lock); > > /* Check for invalidate() race */ > spin_lock(&tree->lock); > - if (entry != zswap_rb_search(&tree->rbroot, swpoffset)) { > - ret = -EAGAIN; > + if (entry != zswap_rb_search(&tree->rbroot, swpoffset)) > goto unlock; > - } > + > /* Hold a reference to prevent a free during writeback */ > zswap_entry_get(entry); > spin_unlock(&tree->lock); > > - ret = zswap_writeback_entry(entry, tree); > + writeback_result = zswap_writeback_entry(entry, tree); > > spin_lock(&tree->lock); > - if (ret) { > - /* Writeback failed, put entry back on LRU */ > - spin_lock(&pool->lru_lock); > - list_move(&entry->lru, &pool->lru); > - spin_unlock(&pool->lru_lock); > + if (writeback_result) { > + zswap_reject_reclaim_fail++; > + zswap_lru_putback(&entry->pool->list_lru, entry); > + ret = LRU_RETRY; > goto put_unlock; > } > + zswap_written_back_pages++; > > /* > * Writeback started successfully, the page now belongs to the > @@ -689,27 +772,93 @@ static int zswap_reclaim_entry(struct zswap_pool *pool) > zswap_entry_put(tree, entry); > unlock: > spin_unlock(&tree->lock); > - return ret ? -EAGAIN : 0; > + spin_lock(lock); > + return ret; > +} > + > +static int shrink_memcg(struct mem_cgroup *memcg) > +{ > + struct zswap_pool *pool; > + int nid, shrunk = 0; > + > + /* > + * Skip zombies because their LRUs are reparented and we would be > + * reclaiming from the parent instead of the dead memcg. > + */ > + if (memcg && !mem_cgroup_online(memcg)) > + return -ENOENT; > + > + pool = zswap_pool_current_get(); > + if (!pool) > + return -EINVAL; > + > + for_each_node_state(nid, N_NORMAL_MEMORY) { > + unsigned long nr_to_walk = 1; > + > + shrunk += list_lru_walk_one(&pool->list_lru, nid, memcg, > + &shrink_memcg_cb, NULL, &nr_to_walk); > + } > + zswap_pool_put(pool); > + return shrunk ? 0 : -EAGAIN; > } > > static void shrink_worker(struct work_struct *w) > { > struct zswap_pool *pool = container_of(w, typeof(*pool), > shrink_work); > + struct mem_cgroup *memcg; > int ret, failures = 0; > > + /* global reclaim will select cgroup in a round-robin fashion. */ > do { > - ret = zswap_reclaim_entry(pool); > - if (ret) { > - zswap_reject_reclaim_fail++; > - if (ret != -EAGAIN) > + spin_lock(&zswap_pools_lock); > + pool->next_shrink = mem_cgroup_iter(NULL, pool->next_shrink, NULL); > + memcg = pool->next_shrink; > + > + /* > + * We need to retry if we have gone through a full round trip, or if we > + * got an offline memcg (or else we risk undoing the effect of the > + * zswap memcg offlining cleanup callback). This is not catastrophic > + * per se, but it will keep the now offlined memcg hostage for a while. > + * > + * Note that if we got an online memcg, we will keep the extra > + * reference in case the original reference obtained by mem_cgroup_iter > + * is dropped by the zswap memcg offlining callback, ensuring that the > + * memcg is not killed when we are reclaiming. > + */ > + if (!memcg) { > + spin_unlock(&zswap_pools_lock); > + if (++failures == MAX_RECLAIM_RETRIES) > break; > + > + goto resched; > + } > + > + if (!mem_cgroup_online(memcg)) { > + /* drop the reference from mem_cgroup_iter() */ > + mem_cgroup_put(memcg); > + pool->next_shrink = NULL; > + spin_unlock(&zswap_pools_lock); > + > if (++failures == MAX_RECLAIM_RETRIES) > break; > + > + goto resched; > } > + spin_unlock(&zswap_pools_lock); > + > + ret = shrink_memcg(memcg); > + /* drop the extra reference */ > + mem_cgroup_put(memcg); > + > + if (ret == -EINVAL) > + break; > + if (ret && ++failures == MAX_RECLAIM_RETRIES) > + break; > + > +resched: > cond_resched(); > } while (!zswap_can_accept()); > - zswap_pool_put(pool); Actually, after staring at this code for a bit more - this looks wrong. This line should not have been removed - this reference putting pairs with the getting from zswap_store(). Looks like some mishap when I rebased and cleaned stuff. Lemme send a fixlet to undo this removal real quick. > } > > static struct zswap_pool *zswap_pool_create(char *type, char *compressor) > @@ -767,8 +916,7 @@ static struct zswap_pool *zswap_pool_create(char *type, char *compressor) > */ > kref_init(&pool->kref); > INIT_LIST_HEAD(&pool->list); > - INIT_LIST_HEAD(&pool->lru); > - spin_lock_init(&pool->lru_lock); > + list_lru_init_memcg(&pool->list_lru, NULL); > INIT_WORK(&pool->shrink_work, shrink_worker); > > zswap_pool_debug("created", pool); > @@ -834,6 +982,13 @@ static void zswap_pool_destroy(struct zswap_pool *pool) > > cpuhp_state_remove_instance(CPUHP_MM_ZSWP_POOL_PREPARE, &pool->node); > free_percpu(pool->acomp_ctx); > + list_lru_destroy(&pool->list_lru); > + > + spin_lock(&zswap_pools_lock); > + mem_cgroup_put(pool->next_shrink); > + pool->next_shrink = NULL; > + spin_unlock(&zswap_pools_lock); > + > for (i = 0; i < ZSWAP_NR_ZPOOLS; i++) > zpool_destroy_pool(pool->zpools[i]); > kfree(pool); > @@ -1081,7 +1236,7 @@ static int zswap_writeback_entry(struct zswap_entry *entry, > /* try to allocate swap cache page */ > mpol = get_task_policy(current); > page = __read_swap_cache_async(swpentry, GFP_KERNEL, mpol, > - NO_INTERLEAVE_INDEX, &page_was_allocated); > + NO_INTERLEAVE_INDEX, &page_was_allocated, true); > if (!page) { > ret = -ENOMEM; > goto fail; > @@ -1152,7 +1307,6 @@ static int zswap_writeback_entry(struct zswap_entry *entry, > /* start writeback */ > __swap_writepage(page, &wbc); > put_page(page); > - zswap_written_back_pages++; > > return ret; > > @@ -1209,6 +1363,7 @@ bool zswap_store(struct folio *folio) > struct scatterlist input, output; > struct crypto_acomp_ctx *acomp_ctx; > struct obj_cgroup *objcg = NULL; > + struct mem_cgroup *memcg = NULL; > struct zswap_pool *pool; > struct zpool *zpool; > unsigned int dlen = PAGE_SIZE; > @@ -1240,15 +1395,15 @@ bool zswap_store(struct folio *folio) > zswap_invalidate_entry(tree, dupentry); > } > spin_unlock(&tree->lock); > - > - /* > - * XXX: zswap reclaim does not work with cgroups yet. Without a > - * cgroup-aware entry LRU, we will push out entries system-wide based on > - * local cgroup limits. > - */ > objcg = get_obj_cgroup_from_folio(folio); > - if (objcg && !obj_cgroup_may_zswap(objcg)) > - goto reject; > + if (objcg && !obj_cgroup_may_zswap(objcg)) { > + memcg = get_mem_cgroup_from_objcg(objcg); > + if (shrink_memcg(memcg)) { > + mem_cgroup_put(memcg); > + goto reject; > + } > + mem_cgroup_put(memcg); > + } > > /* reclaim space if needed */ > if (zswap_is_full()) { > @@ -1265,7 +1420,7 @@ bool zswap_store(struct folio *folio) > } > > /* allocate entry */ > - entry = zswap_entry_cache_alloc(GFP_KERNEL); > + entry = zswap_entry_cache_alloc(GFP_KERNEL, page_to_nid(page)); > if (!entry) { > zswap_reject_kmemcache_fail++; > goto reject; > @@ -1292,6 +1447,15 @@ bool zswap_store(struct folio *folio) > if (!entry->pool) > goto freepage; > > + if (objcg) { > + memcg = get_mem_cgroup_from_objcg(objcg); > + if (memcg_list_lru_alloc(memcg, &entry->pool->list_lru, GFP_KERNEL)) { > + mem_cgroup_put(memcg); > + goto put_pool; > + } > + mem_cgroup_put(memcg); > + } > + > /* compress */ > acomp_ctx = raw_cpu_ptr(entry->pool->acomp_ctx); > > @@ -1370,9 +1534,8 @@ bool zswap_store(struct folio *folio) > zswap_invalidate_entry(tree, dupentry); > } > if (entry->length) { > - spin_lock(&entry->pool->lru_lock); > - list_add(&entry->lru, &entry->pool->lru); > - spin_unlock(&entry->pool->lru_lock); > + INIT_LIST_HEAD(&entry->lru); > + zswap_lru_add(&entry->pool->list_lru, entry); > } > spin_unlock(&tree->lock); > > @@ -1385,6 +1548,7 @@ bool zswap_store(struct folio *folio) > > put_dstmem: > mutex_unlock(acomp_ctx->mutex); > +put_pool: > zswap_pool_put(entry->pool); > freepage: > zswap_entry_cache_free(entry); > @@ -1479,9 +1643,8 @@ bool zswap_load(struct folio *folio) > zswap_invalidate_entry(tree, entry); > folio_mark_dirty(folio); > } else if (entry->length) { > - spin_lock(&entry->pool->lru_lock); > - list_move(&entry->lru, &entry->pool->lru); > - spin_unlock(&entry->pool->lru_lock); > + zswap_lru_del(&entry->pool->list_lru, entry); > + zswap_lru_add(&entry->pool->list_lru, entry); > } > zswap_entry_put(tree, entry); > spin_unlock(&tree->lock); > -- > 2.34.1
