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https://github.com/torvalds/linux
synced 2024-09-06 18:01:05 +00:00
![Chengming Zhou](/assets/img/avatar_default.png)
The SLAB_MEM_SPREAD flag used to be implemented in SLAB, which was
removed as of v6.8-rc1 (see [1]), so it became a dead flag since the
commit 16a1d96835
("mm/slab: remove mm/slab.c and slab_def.h"). And
the series[1] went on to mark it obsolete explicitly to avoid confusion
for users. Here we can just remove all its users, which has no any
functional change.
Signed-off-by: Chengming Zhou <zhouchengming@bytedance.com>
Link: https://lore.kernel.org/all/20240223-slab-cleanup-flags-v2-1-02f1753e8303@suse.cz [1]
Link: https://lore.kernel.org/r/20240224135315.830477-1-chengming.zhou@linux.dev
Signed-off-by: Christian Brauner <brauner@kernel.org>
446 lines
12 KiB
C
446 lines
12 KiB
C
// SPDX-License-Identifier: GPL-2.0-only
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#include <linux/spinlock.h>
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#include <linux/slab.h>
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#include <linux/list.h>
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#include <linux/list_bl.h>
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#include <linux/module.h>
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#include <linux/sched.h>
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#include <linux/workqueue.h>
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#include <linux/mbcache.h>
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/*
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* Mbcache is a simple key-value store. Keys need not be unique, however
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* key-value pairs are expected to be unique (we use this fact in
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* mb_cache_entry_delete_or_get()).
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*
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* Ext2 and ext4 use this cache for deduplication of extended attribute blocks.
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* Ext4 also uses it for deduplication of xattr values stored in inodes.
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* They use hash of data as a key and provide a value that may represent a
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* block or inode number. That's why keys need not be unique (hash of different
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* data may be the same). However user provided value always uniquely
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* identifies a cache entry.
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*
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* We provide functions for creation and removal of entries, search by key,
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* and a special "delete entry with given key-value pair" operation. Fixed
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* size hash table is used for fast key lookups.
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*/
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struct mb_cache {
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/* Hash table of entries */
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struct hlist_bl_head *c_hash;
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/* log2 of hash table size */
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int c_bucket_bits;
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/* Maximum entries in cache to avoid degrading hash too much */
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unsigned long c_max_entries;
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/* Protects c_list, c_entry_count */
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spinlock_t c_list_lock;
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struct list_head c_list;
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/* Number of entries in cache */
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unsigned long c_entry_count;
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struct shrinker *c_shrink;
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/* Work for shrinking when the cache has too many entries */
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struct work_struct c_shrink_work;
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};
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static struct kmem_cache *mb_entry_cache;
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static unsigned long mb_cache_shrink(struct mb_cache *cache,
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unsigned long nr_to_scan);
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static inline struct hlist_bl_head *mb_cache_entry_head(struct mb_cache *cache,
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u32 key)
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{
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return &cache->c_hash[hash_32(key, cache->c_bucket_bits)];
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}
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/*
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* Number of entries to reclaim synchronously when there are too many entries
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* in cache
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*/
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#define SYNC_SHRINK_BATCH 64
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/*
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* mb_cache_entry_create - create entry in cache
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* @cache - cache where the entry should be created
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* @mask - gfp mask with which the entry should be allocated
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* @key - key of the entry
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* @value - value of the entry
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* @reusable - is the entry reusable by others?
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*
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* Creates entry in @cache with key @key and value @value. The function returns
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* -EBUSY if entry with the same key and value already exists in cache.
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* Otherwise 0 is returned.
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*/
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int mb_cache_entry_create(struct mb_cache *cache, gfp_t mask, u32 key,
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u64 value, bool reusable)
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{
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struct mb_cache_entry *entry, *dup;
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struct hlist_bl_node *dup_node;
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struct hlist_bl_head *head;
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/* Schedule background reclaim if there are too many entries */
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if (cache->c_entry_count >= cache->c_max_entries)
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schedule_work(&cache->c_shrink_work);
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/* Do some sync reclaim if background reclaim cannot keep up */
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if (cache->c_entry_count >= 2*cache->c_max_entries)
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mb_cache_shrink(cache, SYNC_SHRINK_BATCH);
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entry = kmem_cache_alloc(mb_entry_cache, mask);
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if (!entry)
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return -ENOMEM;
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INIT_LIST_HEAD(&entry->e_list);
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/*
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* We create entry with two references. One reference is kept by the
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* hash table, the other reference is used to protect us from
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* mb_cache_entry_delete_or_get() until the entry is fully setup. This
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* avoids nesting of cache->c_list_lock into hash table bit locks which
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* is problematic for RT.
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*/
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atomic_set(&entry->e_refcnt, 2);
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entry->e_key = key;
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entry->e_value = value;
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entry->e_flags = 0;
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if (reusable)
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set_bit(MBE_REUSABLE_B, &entry->e_flags);
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head = mb_cache_entry_head(cache, key);
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hlist_bl_lock(head);
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hlist_bl_for_each_entry(dup, dup_node, head, e_hash_list) {
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if (dup->e_key == key && dup->e_value == value) {
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hlist_bl_unlock(head);
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kmem_cache_free(mb_entry_cache, entry);
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return -EBUSY;
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}
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}
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hlist_bl_add_head(&entry->e_hash_list, head);
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hlist_bl_unlock(head);
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spin_lock(&cache->c_list_lock);
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list_add_tail(&entry->e_list, &cache->c_list);
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cache->c_entry_count++;
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spin_unlock(&cache->c_list_lock);
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mb_cache_entry_put(cache, entry);
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return 0;
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}
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EXPORT_SYMBOL(mb_cache_entry_create);
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void __mb_cache_entry_free(struct mb_cache *cache, struct mb_cache_entry *entry)
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{
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struct hlist_bl_head *head;
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head = mb_cache_entry_head(cache, entry->e_key);
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hlist_bl_lock(head);
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hlist_bl_del(&entry->e_hash_list);
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hlist_bl_unlock(head);
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kmem_cache_free(mb_entry_cache, entry);
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}
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EXPORT_SYMBOL(__mb_cache_entry_free);
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/*
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* mb_cache_entry_wait_unused - wait to be the last user of the entry
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*
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* @entry - entry to work on
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*
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* Wait to be the last user of the entry.
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*/
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void mb_cache_entry_wait_unused(struct mb_cache_entry *entry)
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{
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wait_var_event(&entry->e_refcnt, atomic_read(&entry->e_refcnt) <= 2);
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}
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EXPORT_SYMBOL(mb_cache_entry_wait_unused);
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static struct mb_cache_entry *__entry_find(struct mb_cache *cache,
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struct mb_cache_entry *entry,
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u32 key)
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{
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struct mb_cache_entry *old_entry = entry;
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struct hlist_bl_node *node;
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struct hlist_bl_head *head;
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head = mb_cache_entry_head(cache, key);
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hlist_bl_lock(head);
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if (entry && !hlist_bl_unhashed(&entry->e_hash_list))
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node = entry->e_hash_list.next;
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else
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node = hlist_bl_first(head);
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while (node) {
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entry = hlist_bl_entry(node, struct mb_cache_entry,
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e_hash_list);
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if (entry->e_key == key &&
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test_bit(MBE_REUSABLE_B, &entry->e_flags) &&
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atomic_inc_not_zero(&entry->e_refcnt))
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goto out;
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node = node->next;
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}
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entry = NULL;
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out:
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hlist_bl_unlock(head);
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if (old_entry)
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mb_cache_entry_put(cache, old_entry);
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return entry;
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}
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/*
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* mb_cache_entry_find_first - find the first reusable entry with the given key
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* @cache: cache where we should search
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* @key: key to look for
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*
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* Search in @cache for a reusable entry with key @key. Grabs reference to the
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* first reusable entry found and returns the entry.
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*/
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struct mb_cache_entry *mb_cache_entry_find_first(struct mb_cache *cache,
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u32 key)
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{
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return __entry_find(cache, NULL, key);
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}
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EXPORT_SYMBOL(mb_cache_entry_find_first);
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/*
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* mb_cache_entry_find_next - find next reusable entry with the same key
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* @cache: cache where we should search
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* @entry: entry to start search from
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*
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* Finds next reusable entry in the hash chain which has the same key as @entry.
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* If @entry is unhashed (which can happen when deletion of entry races with the
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* search), finds the first reusable entry in the hash chain. The function drops
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* reference to @entry and returns with a reference to the found entry.
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*/
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struct mb_cache_entry *mb_cache_entry_find_next(struct mb_cache *cache,
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struct mb_cache_entry *entry)
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{
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return __entry_find(cache, entry, entry->e_key);
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}
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EXPORT_SYMBOL(mb_cache_entry_find_next);
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/*
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* mb_cache_entry_get - get a cache entry by value (and key)
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* @cache - cache we work with
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* @key - key
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* @value - value
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*/
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struct mb_cache_entry *mb_cache_entry_get(struct mb_cache *cache, u32 key,
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u64 value)
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{
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struct hlist_bl_node *node;
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struct hlist_bl_head *head;
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struct mb_cache_entry *entry;
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head = mb_cache_entry_head(cache, key);
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hlist_bl_lock(head);
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hlist_bl_for_each_entry(entry, node, head, e_hash_list) {
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if (entry->e_key == key && entry->e_value == value &&
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atomic_inc_not_zero(&entry->e_refcnt))
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goto out;
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}
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entry = NULL;
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out:
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hlist_bl_unlock(head);
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return entry;
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}
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EXPORT_SYMBOL(mb_cache_entry_get);
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/* mb_cache_entry_delete_or_get - remove a cache entry if it has no users
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* @cache - cache we work with
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* @key - key
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* @value - value
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*
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* Remove entry from cache @cache with key @key and value @value. The removal
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* happens only if the entry is unused. The function returns NULL in case the
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* entry was successfully removed or there's no entry in cache. Otherwise the
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* function grabs reference of the entry that we failed to delete because it
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* still has users and return it.
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*/
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struct mb_cache_entry *mb_cache_entry_delete_or_get(struct mb_cache *cache,
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u32 key, u64 value)
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{
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struct mb_cache_entry *entry;
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entry = mb_cache_entry_get(cache, key, value);
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if (!entry)
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return NULL;
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/*
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* Drop the ref we got from mb_cache_entry_get() and the initial hash
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* ref if we are the last user
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*/
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if (atomic_cmpxchg(&entry->e_refcnt, 2, 0) != 2)
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return entry;
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spin_lock(&cache->c_list_lock);
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if (!list_empty(&entry->e_list))
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list_del_init(&entry->e_list);
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cache->c_entry_count--;
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spin_unlock(&cache->c_list_lock);
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__mb_cache_entry_free(cache, entry);
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return NULL;
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}
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EXPORT_SYMBOL(mb_cache_entry_delete_or_get);
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/* mb_cache_entry_touch - cache entry got used
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* @cache - cache the entry belongs to
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* @entry - entry that got used
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*
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* Marks entry as used to give hit higher chances of surviving in cache.
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*/
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void mb_cache_entry_touch(struct mb_cache *cache,
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struct mb_cache_entry *entry)
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{
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set_bit(MBE_REFERENCED_B, &entry->e_flags);
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}
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EXPORT_SYMBOL(mb_cache_entry_touch);
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static unsigned long mb_cache_count(struct shrinker *shrink,
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struct shrink_control *sc)
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{
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struct mb_cache *cache = shrink->private_data;
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return cache->c_entry_count;
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}
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/* Shrink number of entries in cache */
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static unsigned long mb_cache_shrink(struct mb_cache *cache,
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unsigned long nr_to_scan)
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{
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struct mb_cache_entry *entry;
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unsigned long shrunk = 0;
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spin_lock(&cache->c_list_lock);
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while (nr_to_scan-- && !list_empty(&cache->c_list)) {
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entry = list_first_entry(&cache->c_list,
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struct mb_cache_entry, e_list);
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/* Drop initial hash reference if there is no user */
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if (test_bit(MBE_REFERENCED_B, &entry->e_flags) ||
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atomic_cmpxchg(&entry->e_refcnt, 1, 0) != 1) {
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clear_bit(MBE_REFERENCED_B, &entry->e_flags);
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list_move_tail(&entry->e_list, &cache->c_list);
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continue;
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}
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list_del_init(&entry->e_list);
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cache->c_entry_count--;
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spin_unlock(&cache->c_list_lock);
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__mb_cache_entry_free(cache, entry);
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shrunk++;
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cond_resched();
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spin_lock(&cache->c_list_lock);
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}
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spin_unlock(&cache->c_list_lock);
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return shrunk;
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}
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static unsigned long mb_cache_scan(struct shrinker *shrink,
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struct shrink_control *sc)
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{
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struct mb_cache *cache = shrink->private_data;
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return mb_cache_shrink(cache, sc->nr_to_scan);
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}
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/* We shrink 1/X of the cache when we have too many entries in it */
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#define SHRINK_DIVISOR 16
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static void mb_cache_shrink_worker(struct work_struct *work)
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{
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struct mb_cache *cache = container_of(work, struct mb_cache,
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c_shrink_work);
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mb_cache_shrink(cache, cache->c_max_entries / SHRINK_DIVISOR);
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}
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/*
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* mb_cache_create - create cache
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* @bucket_bits: log2 of the hash table size
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*
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* Create cache for keys with 2^bucket_bits hash entries.
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*/
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struct mb_cache *mb_cache_create(int bucket_bits)
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{
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struct mb_cache *cache;
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unsigned long bucket_count = 1UL << bucket_bits;
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unsigned long i;
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cache = kzalloc(sizeof(struct mb_cache), GFP_KERNEL);
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if (!cache)
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goto err_out;
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cache->c_bucket_bits = bucket_bits;
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cache->c_max_entries = bucket_count << 4;
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INIT_LIST_HEAD(&cache->c_list);
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spin_lock_init(&cache->c_list_lock);
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cache->c_hash = kmalloc_array(bucket_count,
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sizeof(struct hlist_bl_head),
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GFP_KERNEL);
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if (!cache->c_hash) {
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kfree(cache);
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goto err_out;
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}
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for (i = 0; i < bucket_count; i++)
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INIT_HLIST_BL_HEAD(&cache->c_hash[i]);
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cache->c_shrink = shrinker_alloc(0, "mbcache-shrinker");
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if (!cache->c_shrink) {
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kfree(cache->c_hash);
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kfree(cache);
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goto err_out;
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}
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cache->c_shrink->count_objects = mb_cache_count;
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cache->c_shrink->scan_objects = mb_cache_scan;
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cache->c_shrink->private_data = cache;
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shrinker_register(cache->c_shrink);
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INIT_WORK(&cache->c_shrink_work, mb_cache_shrink_worker);
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return cache;
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err_out:
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return NULL;
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}
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EXPORT_SYMBOL(mb_cache_create);
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/*
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* mb_cache_destroy - destroy cache
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* @cache: the cache to destroy
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*
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* Free all entries in cache and cache itself. Caller must make sure nobody
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* (except shrinker) can reach @cache when calling this.
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*/
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void mb_cache_destroy(struct mb_cache *cache)
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{
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struct mb_cache_entry *entry, *next;
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shrinker_free(cache->c_shrink);
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/*
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* We don't bother with any locking. Cache must not be used at this
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* point.
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*/
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list_for_each_entry_safe(entry, next, &cache->c_list, e_list) {
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list_del(&entry->e_list);
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WARN_ON(atomic_read(&entry->e_refcnt) != 1);
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mb_cache_entry_put(cache, entry);
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}
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kfree(cache->c_hash);
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kfree(cache);
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}
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EXPORT_SYMBOL(mb_cache_destroy);
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static int __init mbcache_init(void)
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{
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mb_entry_cache = KMEM_CACHE(mb_cache_entry, SLAB_RECLAIM_ACCOUNT);
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if (!mb_entry_cache)
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return -ENOMEM;
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return 0;
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}
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static void __exit mbcache_exit(void)
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{
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kmem_cache_destroy(mb_entry_cache);
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}
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module_init(mbcache_init)
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module_exit(mbcache_exit)
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MODULE_AUTHOR("Jan Kara <jack@suse.cz>");
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MODULE_DESCRIPTION("Meta block cache (for extended attributes)");
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MODULE_LICENSE("GPL");
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