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Fri, 20 Mar 2026 12:28:07 -0700 (PDT) From: Nhat Pham To: kasong@tencent.com Cc: Liam.Howlett@oracle.com, akpm@linux-foundation.org, apopple@nvidia.com, axelrasmussen@google.com, baohua@kernel.org, baolin.wang@linux.alibaba.com, bhe@redhat.com, byungchul@sk.com, cgroups@vger.kernel.org, chengming.zhou@linux.dev, chrisl@kernel.org, corbet@lwn.net, david@kernel.org, dev.jain@arm.com, gourry@gourry.net, hannes@cmpxchg.org, hughd@google.com, jannh@google.com, joshua.hahnjy@gmail.com, lance.yang@linux.dev, lenb@kernel.org, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-pm@vger.kernel.org, lorenzo.stoakes@oracle.com, matthew.brost@intel.com, mhocko@suse.com, muchun.song@linux.dev, npache@redhat.com, nphamcs@gmail.com, pavel@kernel.org, peterx@redhat.com, peterz@infradead.org, pfalcato@suse.de, rafael@kernel.org, rakie.kim@sk.com, roman.gushchin@linux.dev, rppt@kernel.org, ryan.roberts@arm.com, shakeel.butt@linux.dev, shikemeng@huaweicloud.com, surenb@google.com, tglx@kernel.org, vbabka@suse.cz, weixugc@google.com, ying.huang@linux.alibaba.com, yosry.ahmed@linux.dev, yuanchu@google.com, zhengqi.arch@bytedance.com, ziy@nvidia.com, kernel-team@meta.com, riel@surriel.com Subject: [PATCH v5 21/21] vswap: batch contiguous vswap free calls Date: Fri, 20 Mar 2026 12:27:35 -0700 Message-ID: <20260320192735.748051-22-nphamcs@gmail.com> X-Mailer: git-send-email 2.52.0 In-Reply-To: <20260320192735.748051-1-nphamcs@gmail.com> References: <20260320192735.748051-1-nphamcs@gmail.com> Precedence: bulk X-Mailing-List: linux-doc@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit In vswap_free(), we release and reacquire the cluster lock for every single entry, even for non-disk-swap backends where the lock drop is unnecessary. Batch consecutive free operations to avoid this overhead. Signed-off-by: Nhat Pham --- include/linux/memcontrol.h | 6 ++ mm/memcontrol.c | 2 +- mm/vswap.c | 185 ++++++++++++++++++++++++------------- 3 files changed, 126 insertions(+), 67 deletions(-) diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h index 0651865a4564f..0f7f5489e1675 100644 --- a/include/linux/memcontrol.h +++ b/include/linux/memcontrol.h @@ -827,6 +827,7 @@ static inline unsigned short mem_cgroup_id(struct mem_cgroup *memcg) return memcg->id.id; } struct mem_cgroup *mem_cgroup_from_id(unsigned short id); +void mem_cgroup_id_put_many(struct mem_cgroup *memcg, unsigned int n); #ifdef CONFIG_SHRINKER_DEBUG static inline unsigned long mem_cgroup_ino(struct mem_cgroup *memcg) @@ -1289,6 +1290,11 @@ static inline struct mem_cgroup *mem_cgroup_from_id(unsigned short id) return NULL; } +static inline void mem_cgroup_id_put_many(struct mem_cgroup *memcg, + unsigned int n) +{ +} + #ifdef CONFIG_SHRINKER_DEBUG static inline unsigned long mem_cgroup_ino(struct mem_cgroup *memcg) { diff --git a/mm/memcontrol.c b/mm/memcontrol.c index 4525c21754e7f..c6d307b8127a8 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -3597,7 +3597,7 @@ void __maybe_unused mem_cgroup_id_get_many(struct mem_cgroup *memcg, refcount_add(n, &memcg->id.ref); } -static void mem_cgroup_id_put_many(struct mem_cgroup *memcg, unsigned int n) +void mem_cgroup_id_put_many(struct mem_cgroup *memcg, unsigned int n) { if (refcount_sub_and_test(n, &memcg->id.ref)) { mem_cgroup_id_remove(memcg); diff --git a/mm/vswap.c b/mm/vswap.c index fa37165cb10d0..82092502130a6 100644 --- a/mm/vswap.c +++ b/mm/vswap.c @@ -482,18 +482,18 @@ static void vswap_cluster_free(struct vswap_cluster *cluster) kvfree_rcu(cluster, rcu); } -static inline void release_vswap_slot(struct vswap_cluster *cluster, - unsigned long index) +static inline void release_vswap_slot_nr(struct vswap_cluster *cluster, + unsigned long index, int nr) { unsigned long slot_index = VSWAP_IDX_WITHIN_CLUSTER_VAL(index); lockdep_assert_held(&cluster->lock); - cluster->count--; + cluster->count -= nr; - bitmap_clear(cluster->bitmap, slot_index, 1); + bitmap_clear(cluster->bitmap, slot_index, nr); /* we only free uncached empty clusters */ - if (refcount_dec_and_test(&cluster->refcnt)) + if (refcount_sub_and_test(nr, &cluster->refcnt)) vswap_cluster_free(cluster); else if (cluster->full && cluster_is_alloc_candidate(cluster)) { cluster->full = false; @@ -506,7 +506,7 @@ static inline void release_vswap_slot(struct vswap_cluster *cluster, } } - atomic_dec(&vswap_used); + atomic_sub(nr, &vswap_used); } /* @@ -528,23 +528,33 @@ void vswap_rmap_set(struct swap_cluster_info *ci, swp_slot_t slot, } /* - * Caller needs to handle races with other operations themselves. + * release_backing - release the backend storage for a given range of virtual + * swap slots. * - * Specifically, this function is safe to be called in contexts where the swap - * entry has been added to the swap cache and the associated folio is locked. - * We cannot race with other accessors, and the swap entry is guaranteed to be - * valid the whole time (since swap cache implies one refcount). + * Entered with the cluster locked, but might drop the lock in between. + * This is because several operations, such as releasing physical swap slots + * (i.e swap_slot_free_nr()) require the cluster to be unlocked to avoid + * deadlocks. * - * We cannot assume that the backends will be of the same type, - * contiguous, etc. We might have a large folio coalesced from subpages with - * mixed backend, which is only rectified when it is reclaimed. + * This is safe, because: + * + * 1. Callers ensure no concurrent modification of the swap entry's internal + * state can occur. This is guaranteed by one of the following: + * - For vswap_free_nr() callers: the swap entry's refcnt (swap count and + * swapcache pin) is down to 0. + * - For vswap_store_folio(), swap_zeromap_folio_set(), and zswap_entry_store() + * callers: the folio is locked and in the swap cache. + * + * 2. The swap entry still holds a refcnt to the cluster, keeping the cluster + * itself valid. + * + * We will exit the function with the cluster re-locked. */ -static void release_backing(swp_entry_t entry, int nr) +static void release_backing(struct vswap_cluster *cluster, swp_entry_t entry, + int nr) { - struct vswap_cluster *cluster = NULL; struct swp_desc *desc; unsigned long flush_nr, phys_swap_start = 0, phys_swap_end = 0; - unsigned long phys_swap_released = 0; unsigned int phys_swap_type = 0; bool need_flushing_phys_swap = false; swp_slot_t flush_slot; @@ -552,9 +562,8 @@ static void release_backing(swp_entry_t entry, int nr) VM_WARN_ON(!entry.val); - rcu_read_lock(); for (i = 0; i < nr; i++) { - desc = vswap_iter(&cluster, entry.val + i); + desc = __vswap_iter(cluster, entry.val + i); VM_WARN_ON(!desc); /* @@ -574,7 +583,6 @@ static void release_backing(swp_entry_t entry, int nr) if (desc->type == VSWAP_ZSWAP && desc->zswap_entry) { zswap_entry_free(desc->zswap_entry); } else if (desc->type == VSWAP_SWAPFILE) { - phys_swap_released++; if (!phys_swap_start) { /* start a new contiguous range of phys swap */ phys_swap_start = swp_slot_offset(desc->slot); @@ -590,56 +598,49 @@ static void release_backing(swp_entry_t entry, int nr) if (need_flushing_phys_swap) { spin_unlock(&cluster->lock); - cluster = NULL; swap_slot_free_nr(flush_slot, flush_nr); + mem_cgroup_uncharge_swap(entry, flush_nr); + spin_lock(&cluster->lock); need_flushing_phys_swap = false; } } - if (cluster) - spin_unlock(&cluster->lock); - rcu_read_unlock(); /* Flush any remaining physical swap range */ if (phys_swap_start) { flush_slot = swp_slot(phys_swap_type, phys_swap_start); flush_nr = phys_swap_end - phys_swap_start; + spin_unlock(&cluster->lock); swap_slot_free_nr(flush_slot, flush_nr); + mem_cgroup_uncharge_swap(entry, flush_nr); + spin_lock(&cluster->lock); } - - if (phys_swap_released) - mem_cgroup_uncharge_swap(entry, phys_swap_released); } +static void __vswap_swap_cgroup_clear(struct vswap_cluster *cluster, + swp_entry_t entry, unsigned int nr_ents); + /* - * Entered with the cluster locked, but might unlock the cluster. - * This is because several operations, such as releasing physical swap slots - * (i.e swap_slot_free_nr()) require the cluster to be unlocked to avoid - * deadlocks. - * - * This is safe, because: - * - * 1. The swap entry to be freed has refcnt (swap count and swapcache pin) - * down to 0, so no one can change its internal state - * - * 2. The swap entry to be freed still holds a refcnt to the cluster, keeping - * the cluster itself valid. - * - * We will exit the function with the cluster re-locked. + * Entered with the cluster locked. We will exit the function with the cluster + * still locked. */ -static void vswap_free(struct vswap_cluster *cluster, struct swp_desc *desc, - swp_entry_t entry) +static void vswap_free_nr(struct vswap_cluster *cluster, swp_entry_t entry, + int nr) { - /* Clear shadow if present */ - if (xa_is_value(desc->shadow)) - desc->shadow = NULL; - spin_unlock(&cluster->lock); + struct swp_desc *desc; + int i; - release_backing(entry, 1); - mem_cgroup_clear_swap(entry, 1); + for (i = 0; i < nr; i++) { + desc = __vswap_iter(cluster, entry.val + i); + /* Clear shadow if present */ + if (xa_is_value(desc->shadow)) + desc->shadow = NULL; + } - /* erase forward mapping and release the virtual slot for reallocation */ - spin_lock(&cluster->lock); - release_vswap_slot(cluster, entry.val); + release_backing(cluster, entry, nr); + __vswap_swap_cgroup_clear(cluster, entry, nr); + + /* erase forward mapping and release the virtual slots for reallocation */ + release_vswap_slot_nr(cluster, entry.val, nr); } /** @@ -818,18 +819,32 @@ static bool vswap_free_nr_any_cache_only(swp_entry_t entry, int nr) struct vswap_cluster *cluster = NULL; struct swp_desc *desc; bool ret = false; - int i; + swp_entry_t free_start; + int i, free_nr = 0; + free_start.val = 0; rcu_read_lock(); for (i = 0; i < nr; i++) { + /* flush pending free batch at cluster boundary */ + if (free_nr && !VSWAP_IDX_WITHIN_CLUSTER_VAL(entry.val)) { + vswap_free_nr(cluster, free_start, free_nr); + free_nr = 0; + } desc = vswap_iter(&cluster, entry.val); VM_WARN_ON(!desc); ret |= (desc->swap_count == 1 && desc->in_swapcache); desc->swap_count--; - if (!desc->swap_count && !desc->in_swapcache) - vswap_free(cluster, desc, entry); + if (!desc->swap_count && !desc->in_swapcache) { + if (!free_nr++) + free_start = entry; + } else if (free_nr) { + vswap_free_nr(cluster, free_start, free_nr); + free_nr = 0; + } entry.val++; } + if (free_nr) + vswap_free_nr(cluster, free_start, free_nr); if (cluster) spin_unlock(&cluster->lock); rcu_read_unlock(); @@ -952,19 +967,33 @@ void swapcache_clear(swp_entry_t entry, int nr) { struct vswap_cluster *cluster = NULL; struct swp_desc *desc; - int i; + swp_entry_t free_start; + int i, free_nr = 0; if (!nr) return; + free_start.val = 0; rcu_read_lock(); for (i = 0; i < nr; i++) { + /* flush pending free batch at cluster boundary */ + if (free_nr && !VSWAP_IDX_WITHIN_CLUSTER_VAL(entry.val)) { + vswap_free_nr(cluster, free_start, free_nr); + free_nr = 0; + } desc = vswap_iter(&cluster, entry.val); desc->in_swapcache = false; - if (!desc->swap_count) - vswap_free(cluster, desc, entry); + if (!desc->swap_count) { + if (!free_nr++) + free_start = entry; + } else if (free_nr) { + vswap_free_nr(cluster, free_start, free_nr); + free_nr = 0; + } entry.val++; } + if (free_nr) + vswap_free_nr(cluster, free_start, free_nr); if (cluster) spin_unlock(&cluster->lock); rcu_read_unlock(); @@ -1105,11 +1134,13 @@ void vswap_store_folio(swp_entry_t entry, struct folio *folio) VM_BUG_ON(!folio_test_locked(folio)); VM_BUG_ON(folio->swap.val != entry.val); - release_backing(entry, nr); - rcu_read_lock(); + desc = vswap_iter(&cluster, entry.val); + VM_WARN_ON(!desc); + release_backing(cluster, entry, nr); + for (i = 0; i < nr; i++) { - desc = vswap_iter(&cluster, entry.val + i); + desc = __vswap_iter(cluster, entry.val + i); VM_WARN_ON(!desc); desc->type = VSWAP_FOLIO; desc->swap_cache = folio; @@ -1134,11 +1165,13 @@ void swap_zeromap_folio_set(struct folio *folio) VM_BUG_ON(!folio_test_locked(folio)); VM_BUG_ON(!entry.val); - release_backing(entry, nr); - rcu_read_lock(); + desc = vswap_iter(&cluster, entry.val); + VM_WARN_ON(!desc); + release_backing(cluster, entry, nr); + for (i = 0; i < nr; i++) { - desc = vswap_iter(&cluster, entry.val + i); + desc = __vswap_iter(cluster, entry.val + i); VM_WARN_ON(!desc); desc->type = VSWAP_ZERO; } @@ -1772,11 +1805,10 @@ void zswap_entry_store(swp_entry_t swpentry, struct zswap_entry *entry) struct vswap_cluster *cluster = NULL; struct swp_desc *desc; - release_backing(swpentry, 1); - rcu_read_lock(); desc = vswap_iter(&cluster, swpentry.val); VM_WARN_ON(!desc); + release_backing(cluster, swpentry, 1); desc->zswap_entry = entry; desc->type = VSWAP_ZSWAP; spin_unlock(&cluster->lock); @@ -1850,6 +1882,22 @@ static unsigned short __vswap_cgroup_record(struct vswap_cluster *cluster, return oldid; } +/* + * Clear swap cgroup for a range of swap entries. + * Entered with the cluster locked. Caller must be under rcu_read_lock(). + */ +static void __vswap_swap_cgroup_clear(struct vswap_cluster *cluster, + swp_entry_t entry, unsigned int nr_ents) +{ + unsigned short id; + struct mem_cgroup *memcg; + + id = __vswap_cgroup_record(cluster, entry, 0, nr_ents); + memcg = mem_cgroup_from_id(id); + if (memcg) + mem_cgroup_id_put_many(memcg, nr_ents); +} + static unsigned short vswap_cgroup_record(swp_entry_t entry, unsigned short memcgid, unsigned int nr_ents) { @@ -1955,6 +2003,11 @@ unsigned short lookup_swap_cgroup_id(swp_entry_t entry) rcu_read_unlock(); return ret; } +#else /* !CONFIG_MEMCG */ +static void __vswap_swap_cgroup_clear(struct vswap_cluster *cluster, + swp_entry_t entry, unsigned int nr_ents) +{ +} #endif /* CONFIG_MEMCG */ int vswap_init(void) -- 2.52.0