diff options
Diffstat (limited to 'lib')
| -rw-r--r-- | lib/Kconfig | 3 | ||||
| -rw-r--r-- | lib/Makefile | 2 | ||||
| -rw-r--r-- | lib/lru_cache.c | 560 |
3 files changed, 565 insertions, 0 deletions
diff --git a/lib/Kconfig b/lib/Kconfig index bb1326d3839..1cfe51628e1 100644 --- a/lib/Kconfig +++ b/lib/Kconfig @@ -200,4 +200,7 @@ config NLATTR config GENERIC_ATOMIC64 bool +config LRU_CACHE + tristate + endmenu diff --git a/lib/Makefile b/lib/Makefile index 2e78277eff9..347ad8db29d 100644 --- a/lib/Makefile +++ b/lib/Makefile @@ -91,6 +91,8 @@ obj-$(CONFIG_DYNAMIC_DEBUG) += dynamic_debug.o obj-$(CONFIG_NLATTR) += nlattr.o +obj-$(CONFIG_LRU_CACHE) += lru_cache.o + obj-$(CONFIG_DMA_API_DEBUG) += dma-debug.o obj-$(CONFIG_GENERIC_CSUM) += checksum.o diff --git a/lib/lru_cache.c b/lib/lru_cache.c new file mode 100644 index 00000000000..270de9d31b8 --- /dev/null +++ b/lib/lru_cache.c @@ -0,0 +1,560 @@ +/* + lru_cache.c + + This file is part of DRBD by Philipp Reisner and Lars Ellenberg. + + Copyright (C) 2003-2008, LINBIT Information Technologies GmbH. + Copyright (C) 2003-2008, Philipp Reisner <philipp.reisner@linbit.com>. + Copyright (C) 2003-2008, Lars Ellenberg <lars.ellenberg@linbit.com>. + + drbd is free software; you can redistribute it and/or modify + it under the terms of the GNU General Public License as published by + the Free Software Foundation; either version 2, or (at your option) + any later version. + + drbd is distributed in the hope that it will be useful, + but WITHOUT ANY WARRANTY; without even the implied warranty of + MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the + GNU General Public License for more details. + + You should have received a copy of the GNU General Public License + along with drbd; see the file COPYING. If not, write to + the Free Software Foundation, 675 Mass Ave, Cambridge, MA 02139, USA. + + */ + +#include <linux/module.h> +#include <linux/bitops.h> +#include <linux/slab.h> +#include <linux/string.h> /* for memset */ +#include <linux/seq_file.h> /* for seq_printf */ +#include <linux/lru_cache.h> + +MODULE_AUTHOR("Philipp Reisner <phil@linbit.com>, " + "Lars Ellenberg <lars@linbit.com>"); +MODULE_DESCRIPTION("lru_cache - Track sets of hot objects"); +MODULE_LICENSE("GPL"); + +/* this is developers aid only. + * it catches concurrent access (lack of locking on the users part) */ +#define PARANOIA_ENTRY() do { \ + BUG_ON(!lc); \ + BUG_ON(!lc->nr_elements); \ + BUG_ON(test_and_set_bit(__LC_PARANOIA, &lc->flags)); \ +} while (0) + +#define RETURN(x...) do { \ + clear_bit(__LC_PARANOIA, &lc->flags); \ + smp_mb__after_clear_bit(); return x ; } while (0) + +/* BUG() if e is not one of the elements tracked by lc */ +#define PARANOIA_LC_ELEMENT(lc, e) do { \ + struct lru_cache *lc_ = (lc); \ + struct lc_element *e_ = (e); \ + unsigned i = e_->lc_index; \ + BUG_ON(i >= lc_->nr_elements); \ + BUG_ON(lc_->lc_element[i] != e_); } while (0) + +/** + * lc_create - prepares to track objects in an active set + * @name: descriptive name only used in lc_seq_printf_stats and lc_seq_dump_details + * @e_count: number of elements allowed to be active simultaneously + * @e_size: size of the tracked objects + * @e_off: offset to the &struct lc_element member in a tracked object + * + * Returns a pointer to a newly initialized struct lru_cache on success, + * or NULL on (allocation) failure. + */ +struct lru_cache *lc_create(const char *name, struct kmem_cache *cache, + unsigned e_count, size_t e_size, size_t e_off) +{ + struct hlist_head *slot = NULL; + struct lc_element **element = NULL; + struct lru_cache *lc; + struct lc_element *e; + unsigned cache_obj_size = kmem_cache_size(cache); + unsigned i; + + WARN_ON(cache_obj_size < e_size); + if (cache_obj_size < e_size) + return NULL; + + /* e_count too big; would probably fail the allocation below anyways. + * for typical use cases, e_count should be few thousand at most. */ + if (e_count > LC_MAX_ACTIVE) + return NULL; + + slot = kzalloc(e_count * sizeof(struct hlist_head*), GFP_KERNEL); + if (!slot) + goto out_fail; + element = kzalloc(e_count * sizeof(struct lc_element *), GFP_KERNEL); + if (!element) + goto out_fail; + + lc = kzalloc(sizeof(*lc), GFP_KERNEL); + if (!lc) + goto out_fail; + + INIT_LIST_HEAD(&lc->in_use); + INIT_LIST_HEAD(&lc->lru); + INIT_LIST_HEAD(&lc->free); + + lc->name = name; + lc->element_size = e_size; + lc->element_off = e_off; + lc->nr_elements = e_count; + lc->new_number = LC_FREE; + lc->lc_cache = cache; + lc->lc_element = element; + lc->lc_slot = slot; + + /* preallocate all objects */ + for (i = 0; i < e_count; i++) { + void *p = kmem_cache_alloc(cache, GFP_KERNEL); + if (!p) + break; + memset(p, 0, lc->element_size); + e = p + e_off; + e->lc_index = i; + e->lc_number = LC_FREE; + list_add(&e->list, &lc->free); + element[i] = e; + } + if (i == e_count) + return lc; + + /* else: could not allocate all elements, give up */ + for (i--; i; i--) { + void *p = element[i]; + kmem_cache_free(cache, p - e_off); + } + kfree(lc); +out_fail: + kfree(element); + kfree(slot); + return NULL; +} + +void lc_free_by_index(struct lru_cache *lc, unsigned i) +{ + void *p = lc->lc_element[i]; + WARN_ON(!p); + if (p) { + p -= lc->element_off; + kmem_cache_free(lc->lc_cache, p); + } +} + +/** + * lc_destroy - frees memory allocated by lc_create() + * @lc: the lru cache to destroy + */ +void lc_destroy(struct lru_cache *lc) +{ + unsigned i; + if (!lc) + return; + for (i = 0; i < lc->nr_elements; i++) + lc_free_by_index(lc, i); + kfree(lc->lc_element); + kfree(lc->lc_slot); + kfree(lc); +} + +/** + * lc_reset - does a full reset for @lc and the hash table slots. + * @lc: the lru cache to operate on + * + * It is roughly the equivalent of re-allocating a fresh lru_cache object, + * basically a short cut to lc_destroy(lc); lc = lc_create(...); + */ +void lc_reset(struct lru_cache *lc) +{ + unsigned i; + + INIT_LIST_HEAD(&lc->in_use); + INIT_LIST_HEAD(&lc->lru); + INIT_LIST_HEAD(&lc->free); + lc->used = 0; + lc->hits = 0; + lc->misses = 0; + lc->starving = 0; + lc->dirty = 0; + lc->changed = 0; + lc->flags = 0; + lc->changing_element = NULL; + lc->new_number = LC_FREE; + memset(lc->lc_slot, 0, sizeof(struct hlist_head) * lc->nr_elements); + + for (i = 0; i < lc->nr_elements; i++) { + struct lc_element *e = lc->lc_element[i]; + void *p = e; + p -= lc->element_off; + memset(p, 0, lc->element_size); + /* re-init it */ + e->lc_index = i; + e->lc_number = LC_FREE; + list_add(&e->list, &lc->free); + } +} + +/** + * lc_seq_printf_stats - print stats about @lc into @seq + * @seq: the seq_file to print into + * @lc: the lru cache to print statistics of + */ +size_t lc_seq_printf_stats(struct seq_file *seq, struct lru_cache *lc) +{ + /* NOTE: + * total calls to lc_get are + * (starving + hits + misses) + * misses include "dirty" count (update from an other thread in + * progress) and "changed", when this in fact lead to an successful + * update of the cache. + */ + return seq_printf(seq, "\t%s: used:%u/%u " + "hits:%lu misses:%lu starving:%lu dirty:%lu changed:%lu\n", + lc->name, lc->used, lc->nr_elements, + lc->hits, lc->misses, lc->starving, lc->dirty, lc->changed); +} + +static struct hlist_head *lc_hash_slot(struct lru_cache *lc, unsigned int enr) +{ + return lc->lc_slot + (enr % lc->nr_elements); +} + + +/** + * lc_find - find element by label, if present in the hash table + * @lc: The lru_cache object + * @enr: element number + * + * Returns the pointer to an element, if the element with the requested + * "label" or element number is present in the hash table, + * or NULL if not found. Does not change the refcnt. + */ +struct lc_element *lc_find(struct lru_cache *lc, unsigned int enr) +{ + struct hlist_node *n; + struct lc_element *e; + + BUG_ON(!lc); + BUG_ON(!lc->nr_elements); + hlist_for_each_entry(e, n, lc_hash_slot(lc, enr), colision) { + if (e->lc_number == enr) + return e; + } + return NULL; +} + +/* returned element will be "recycled" immediately */ +static struct lc_element *lc_evict(struct lru_cache *lc) +{ + struct list_head *n; + struct lc_element *e; + + if (list_empty(&lc->lru)) + return NULL; + + n = lc->lru.prev; + e = list_entry(n, struct lc_element, list); + + PARANOIA_LC_ELEMENT(lc, e); + + list_del(&e->list); + hlist_del(&e->colision); + return e; +} + +/** + * lc_del - removes an element from the cache + * @lc: The lru_cache object + * @e: The element to remove + * + * @e must be unused (refcnt == 0). Moves @e from "lru" to "free" list, + * sets @e->enr to %LC_FREE. + */ +void lc_del(struct lru_cache *lc, struct lc_element *e) +{ + PARANOIA_ENTRY(); + PARANOIA_LC_ELEMENT(lc, e); + BUG_ON(e->refcnt); + + e->lc_number = LC_FREE; + hlist_del_init(&e->colision); + list_move(&e->list, &lc->free); + RETURN(); +} + +static struct lc_element *lc_get_unused_element(struct lru_cache *lc) +{ + struct list_head *n; + + if (list_empty(&lc->free)) + return lc_evict(lc); + + n = lc->free.next; + list_del(n); + return list_entry(n, struct lc_element, list); +} + +static int lc_unused_element_available(struct lru_cache *lc) +{ + if (!list_empty(&lc->free)) + return 1; /* something on the free list */ + if (!list_empty(&lc->lru)) + return 1; /* something to evict */ + + return 0; +} + + +/** + * lc_get - get element by label, maybe change the active set + * @lc: the lru cache to operate on + * @enr: the label to look up + * + * Finds an element in the cache, increases its usage count, + * "touches" and returns it. + * + * In case the requested number is not present, it needs to be added to the + * cache. Therefore it is possible that an other element becomes evicted from + * the cache. In either case, the user is notified so he is able to e.g. keep + * a persistent log of the cache changes, and therefore the objects in use. + * + * Return values: + * NULL + * The cache was marked %LC_STARVING, + * or the requested label was not in the active set + * and a changing transaction is still pending (@lc was marked %LC_DIRTY). + * Or no unused or free element could be recycled (@lc will be marked as + * %LC_STARVING, blocking further lc_get() operations). + * + * pointer to the element with the REQUESTED element number. + * In this case, it can be used right away + * + * pointer to an UNUSED element with some different element number, + * where that different number may also be %LC_FREE. + * + * In this case, the cache is marked %LC_DIRTY (blocking further changes), + * and the returned element pointer is removed from the lru list and + * hash collision chains. The user now should do whatever housekeeping + * is necessary. + * Then he must call lc_changed(lc,element_pointer), to finish + * the change. + * + * NOTE: The user needs to check the lc_number on EACH use, so he recognizes + * any cache set change. + */ +struct lc_element *lc_get(struct lru_cache *lc, unsigned int enr) +{ + struct lc_element *e; + + PARANOIA_ENTRY(); + if (lc->flags & LC_STARVING) { + ++lc->starving; + RETURN(NULL); + } + + e = lc_find(lc, enr); + if (e) { + ++lc->hits; + if (e->refcnt++ == 0) + lc->used++; + list_move(&e->list, &lc->in_use); /* Not evictable... */ + RETURN(e); + } + + ++lc->misses; + + /* In case there is nothing available and we can not kick out + * the LRU element, we have to wait ... + */ + if (!lc_unused_element_available(lc)) { + __set_bit(__LC_STARVING, &lc->flags); + RETURN(NULL); + } + + /* it was not present in the active set. + * we are going to recycle an unused (or even "free") element. + * user may need to commit a transaction to record that change. + * we serialize on flags & TF_DIRTY */ + if (test_and_set_bit(__LC_DIRTY, &lc->flags)) { + ++lc->dirty; + RETURN(NULL); + } + + e = lc_get_unused_element(lc); + BUG_ON(!e); + + clear_bit(__LC_STARVING, &lc->flags); + BUG_ON(++e->refcnt != 1); + lc->used++; + + lc->changing_element = e; + lc->new_number = enr; + + RETURN(e); +} + +/* similar to lc_get, + * but only gets a new reference on an existing element. + * you either get the requested element, or NULL. + * will be consolidated into one function. + */ +struct lc_element *lc_try_get(struct lru_cache *lc, unsigned int enr) +{ + struct lc_element *e; + + PARANOIA_ENTRY(); + if (lc->flags & LC_STARVING) { + ++lc->starving; + RETURN(NULL); + } + + e = lc_find(lc, enr); + if (e) { + ++lc->hits; + if (e->refcnt++ == 0) + lc->used++; + list_move(&e->list, &lc->in_use); /* Not evictable... */ + } + RETURN(e); +} + +/** + * lc_changed - tell @lc that the change has been recorded + * @lc: the lru cache to operate on + * @e: the element pending label change + */ +void lc_changed(struct lru_cache *lc, struct lc_element *e) +{ + PARANOIA_ENTRY(); + BUG_ON(e != lc->changing_element); + PARANOIA_LC_ELEMENT(lc, e); + ++lc->changed; + e->lc_number = lc->new_number; + list_add(&e->list, &lc->in_use); + hlist_add_head(&e->colision, lc_hash_slot(lc, lc->new_number)); + lc->changing_element = NULL; + lc->new_number = LC_FREE; + clear_bit(__LC_DIRTY, &lc->flags); + smp_mb__after_clear_bit(); + RETURN(); +} + + +/** + * lc_put - give up refcnt of @e + * @lc: the lru cache to operate on + * @e: the element to put + * + * If refcnt reaches zero, the element is moved to the lru list, + * and a %LC_STARVING (if set) is cleared. + * Returns the new (post-decrement) refcnt. + */ +unsigned int lc_put(struct lru_cache *lc, struct lc_element *e) +{ + PARANOIA_ENTRY(); + PARANOIA_LC_ELEMENT(lc, e); + BUG_ON(e->refcnt == 0); + BUG_ON(e == lc->changing_element); + if (--e->refcnt == 0) { + /* move it to the front of LRU. */ + list_move(&e->list, &lc->lru); + lc->used--; + clear_bit(__LC_STARVING, &lc->flags); + smp_mb__after_clear_bit(); + } + RETURN(e->refcnt); +} + +/** + * lc_element_by_index + * @lc: the lru cache to operate on + * @i: the index of the element to return + */ +struct lc_element *lc_element_by_index(struct lru_cache *lc, unsigned i) +{ + BUG_ON(i >= lc->nr_elements); + BUG_ON(lc->lc_element[i] == NULL); + BUG_ON(lc->lc_element[i]->lc_index != i); + return lc->lc_element[i]; +} + +/** + * lc_index_of + * @lc: the lru cache to operate on + * @e: the element to query for its index position in lc->element + */ +unsigned int lc_index_of(struct lru_cache *lc, struct lc_element *e) +{ + PARANOIA_LC_ELEMENT(lc, e); + return e->lc_index; +} + +/** + * lc_set - associate index with label + * @lc: the lru cache to operate on + * @enr: the label to set + * @index: the element index to associate label with. + * + * Used to initialize the active set to some previously recorded state. + */ +void lc_set(struct lru_cache *lc, unsigned int enr, int index) +{ + struct lc_element *e; + + if (index < 0 || index >= lc->nr_elements) + return; + + e = lc_element_by_index(lc, index); + e->lc_number = enr; + + hlist_del_init(&e->colision); + hlist_add_head(&e->colision, lc_hash_slot(lc, enr)); + list_move(&e->list, e->refcnt ? &lc->in_use : &lc->lru); +} + +/** + * lc_dump - Dump a complete LRU cache to seq in textual form. + * @lc: the lru cache to operate on + * @seq: the &struct seq_file pointer to seq_printf into + * @utext: user supplied "heading" or other info + * @detail: function pointer the user may provide to dump further details + * of the object the lc_element is embedded in. + */ +void lc_seq_dump_details(struct seq_file *seq, struct lru_cache *lc, char *utext, + void (*detail) (struct seq_file *, struct lc_element *)) +{ + unsigned int nr_elements = lc->nr_elements; + struct lc_element *e; + int i; + + seq_printf(seq, "\tnn: lc_number refcnt %s\n ", utext); + for (i = 0; i < nr_elements; i++) { + e = lc_element_by_index(lc, i); + if (e->lc_number == LC_FREE) { + seq_printf(seq, "\t%2d: FREE\n", i); + } else { + seq_printf(seq, "\t%2d: %4u %4u ", i, + e->lc_number, e->refcnt); + detail(seq, e); + } + } +} + +EXPORT_SYMBOL(lc_create); +EXPORT_SYMBOL(lc_reset); +EXPORT_SYMBOL(lc_destroy); +EXPORT_SYMBOL(lc_set); +EXPORT_SYMBOL(lc_del); +EXPORT_SYMBOL(lc_try_get); +EXPORT_SYMBOL(lc_find); +EXPORT_SYMBOL(lc_get); +EXPORT_SYMBOL(lc_put); +EXPORT_SYMBOL(lc_changed); +EXPORT_SYMBOL(lc_element_by_index); +EXPORT_SYMBOL(lc_index_of); +EXPORT_SYMBOL(lc_seq_printf_stats); +EXPORT_SYMBOL(lc_seq_dump_details); |