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![Joe Perches](/assets/img/avatar_default.png)
The seq_printf return value, because it's frequently misused,
will eventually be converted to void.
See: commit 1f33c41c03
("seq_file: Rename seq_overflow() to
seq_has_overflowed() and make public")
Signed-off-by: Joe Perches <joe@perches.com>
Cc: Lars Ellenberg <drbd-dev@lists.linbit.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
690 lines
19 KiB
C
690 lines
19 KiB
C
/*
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lru_cache.c
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This file is part of DRBD by Philipp Reisner and Lars Ellenberg.
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Copyright (C) 2003-2008, LINBIT Information Technologies GmbH.
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Copyright (C) 2003-2008, Philipp Reisner <philipp.reisner@linbit.com>.
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Copyright (C) 2003-2008, Lars Ellenberg <lars.ellenberg@linbit.com>.
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drbd is free software; you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation; either version 2, or (at your option)
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any later version.
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drbd is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with drbd; see the file COPYING. If not, write to
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the Free Software Foundation, 675 Mass Ave, Cambridge, MA 02139, USA.
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*/
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#include <linux/module.h>
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#include <linux/bitops.h>
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#include <linux/slab.h>
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#include <linux/string.h> /* for memset */
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#include <linux/seq_file.h> /* for seq_printf */
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#include <linux/lru_cache.h>
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MODULE_AUTHOR("Philipp Reisner <phil@linbit.com>, "
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"Lars Ellenberg <lars@linbit.com>");
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MODULE_DESCRIPTION("lru_cache - Track sets of hot objects");
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MODULE_LICENSE("GPL");
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/* this is developers aid only.
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* it catches concurrent access (lack of locking on the users part) */
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#define PARANOIA_ENTRY() do { \
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BUG_ON(!lc); \
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BUG_ON(!lc->nr_elements); \
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BUG_ON(test_and_set_bit(__LC_PARANOIA, &lc->flags)); \
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} while (0)
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#define RETURN(x...) do { \
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clear_bit_unlock(__LC_PARANOIA, &lc->flags); \
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return x ; } while (0)
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/* BUG() if e is not one of the elements tracked by lc */
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#define PARANOIA_LC_ELEMENT(lc, e) do { \
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struct lru_cache *lc_ = (lc); \
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struct lc_element *e_ = (e); \
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unsigned i = e_->lc_index; \
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BUG_ON(i >= lc_->nr_elements); \
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BUG_ON(lc_->lc_element[i] != e_); } while (0)
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/* We need to atomically
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* - try to grab the lock (set LC_LOCKED)
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* - only if there is no pending transaction
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* (neither LC_DIRTY nor LC_STARVING is set)
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* Because of PARANOIA_ENTRY() above abusing lc->flags as well,
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* it is not sufficient to just say
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* return 0 == cmpxchg(&lc->flags, 0, LC_LOCKED);
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*/
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int lc_try_lock(struct lru_cache *lc)
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{
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unsigned long val;
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do {
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val = cmpxchg(&lc->flags, 0, LC_LOCKED);
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} while (unlikely (val == LC_PARANOIA));
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/* Spin until no-one is inside a PARANOIA_ENTRY()/RETURN() section. */
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return 0 == val;
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#if 0
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/* Alternative approach, spin in case someone enters or leaves a
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* PARANOIA_ENTRY()/RETURN() section. */
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unsigned long old, new, val;
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do {
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old = lc->flags & LC_PARANOIA;
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new = old | LC_LOCKED;
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val = cmpxchg(&lc->flags, old, new);
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} while (unlikely (val == (old ^ LC_PARANOIA)));
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return old == val;
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#endif
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}
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/**
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* lc_create - prepares to track objects in an active set
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* @name: descriptive name only used in lc_seq_printf_stats and lc_seq_dump_details
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* @max_pending_changes: maximum changes to accumulate until a transaction is required
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* @e_count: number of elements allowed to be active simultaneously
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* @e_size: size of the tracked objects
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* @e_off: offset to the &struct lc_element member in a tracked object
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*
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* Returns a pointer to a newly initialized struct lru_cache on success,
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* or NULL on (allocation) failure.
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*/
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struct lru_cache *lc_create(const char *name, struct kmem_cache *cache,
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unsigned max_pending_changes,
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unsigned e_count, size_t e_size, size_t e_off)
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{
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struct hlist_head *slot = NULL;
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struct lc_element **element = NULL;
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struct lru_cache *lc;
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struct lc_element *e;
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unsigned cache_obj_size = kmem_cache_size(cache);
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unsigned i;
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WARN_ON(cache_obj_size < e_size);
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if (cache_obj_size < e_size)
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return NULL;
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/* e_count too big; would probably fail the allocation below anyways.
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* for typical use cases, e_count should be few thousand at most. */
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if (e_count > LC_MAX_ACTIVE)
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return NULL;
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slot = kcalloc(e_count, sizeof(struct hlist_head), GFP_KERNEL);
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if (!slot)
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goto out_fail;
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element = kzalloc(e_count * sizeof(struct lc_element *), GFP_KERNEL);
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if (!element)
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goto out_fail;
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lc = kzalloc(sizeof(*lc), GFP_KERNEL);
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if (!lc)
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goto out_fail;
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INIT_LIST_HEAD(&lc->in_use);
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INIT_LIST_HEAD(&lc->lru);
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INIT_LIST_HEAD(&lc->free);
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INIT_LIST_HEAD(&lc->to_be_changed);
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lc->name = name;
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lc->element_size = e_size;
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lc->element_off = e_off;
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lc->nr_elements = e_count;
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lc->max_pending_changes = max_pending_changes;
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lc->lc_cache = cache;
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lc->lc_element = element;
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lc->lc_slot = slot;
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/* preallocate all objects */
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for (i = 0; i < e_count; i++) {
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void *p = kmem_cache_alloc(cache, GFP_KERNEL);
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if (!p)
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break;
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memset(p, 0, lc->element_size);
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e = p + e_off;
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e->lc_index = i;
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e->lc_number = LC_FREE;
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e->lc_new_number = LC_FREE;
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list_add(&e->list, &lc->free);
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element[i] = e;
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}
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if (i == e_count)
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return lc;
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/* else: could not allocate all elements, give up */
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for (i--; i; i--) {
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void *p = element[i];
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kmem_cache_free(cache, p - e_off);
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}
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kfree(lc);
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out_fail:
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kfree(element);
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kfree(slot);
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return NULL;
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}
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static void lc_free_by_index(struct lru_cache *lc, unsigned i)
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{
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void *p = lc->lc_element[i];
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WARN_ON(!p);
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if (p) {
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p -= lc->element_off;
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kmem_cache_free(lc->lc_cache, p);
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}
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}
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/**
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* lc_destroy - frees memory allocated by lc_create()
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* @lc: the lru cache to destroy
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*/
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void lc_destroy(struct lru_cache *lc)
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{
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unsigned i;
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if (!lc)
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return;
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for (i = 0; i < lc->nr_elements; i++)
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lc_free_by_index(lc, i);
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kfree(lc->lc_element);
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kfree(lc->lc_slot);
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kfree(lc);
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}
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/**
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* lc_reset - does a full reset for @lc and the hash table slots.
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* @lc: the lru cache to operate on
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*
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* It is roughly the equivalent of re-allocating a fresh lru_cache object,
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* basically a short cut to lc_destroy(lc); lc = lc_create(...);
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*/
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void lc_reset(struct lru_cache *lc)
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{
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unsigned i;
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INIT_LIST_HEAD(&lc->in_use);
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INIT_LIST_HEAD(&lc->lru);
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INIT_LIST_HEAD(&lc->free);
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INIT_LIST_HEAD(&lc->to_be_changed);
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lc->used = 0;
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lc->hits = 0;
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lc->misses = 0;
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lc->starving = 0;
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lc->locked = 0;
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lc->changed = 0;
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lc->pending_changes = 0;
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lc->flags = 0;
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memset(lc->lc_slot, 0, sizeof(struct hlist_head) * lc->nr_elements);
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for (i = 0; i < lc->nr_elements; i++) {
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struct lc_element *e = lc->lc_element[i];
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void *p = e;
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p -= lc->element_off;
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memset(p, 0, lc->element_size);
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/* re-init it */
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e->lc_index = i;
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e->lc_number = LC_FREE;
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e->lc_new_number = LC_FREE;
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list_add(&e->list, &lc->free);
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}
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}
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/**
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* lc_seq_printf_stats - print stats about @lc into @seq
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* @seq: the seq_file to print into
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* @lc: the lru cache to print statistics of
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*/
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size_t lc_seq_printf_stats(struct seq_file *seq, struct lru_cache *lc)
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{
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/* NOTE:
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* total calls to lc_get are
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* (starving + hits + misses)
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* misses include "locked" count (update from an other thread in
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* progress) and "changed", when this in fact lead to an successful
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* update of the cache.
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*/
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seq_printf(seq, "\t%s: used:%u/%u hits:%lu misses:%lu starving:%lu locked:%lu changed:%lu\n",
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lc->name, lc->used, lc->nr_elements,
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lc->hits, lc->misses, lc->starving, lc->locked, lc->changed);
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return 0;
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}
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static struct hlist_head *lc_hash_slot(struct lru_cache *lc, unsigned int enr)
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{
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return lc->lc_slot + (enr % lc->nr_elements);
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}
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static struct lc_element *__lc_find(struct lru_cache *lc, unsigned int enr,
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bool include_changing)
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{
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struct lc_element *e;
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BUG_ON(!lc);
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BUG_ON(!lc->nr_elements);
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hlist_for_each_entry(e, lc_hash_slot(lc, enr), colision) {
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/* "about to be changed" elements, pending transaction commit,
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* are hashed by their "new number". "Normal" elements have
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* lc_number == lc_new_number. */
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if (e->lc_new_number != enr)
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continue;
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if (e->lc_new_number == e->lc_number || include_changing)
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return e;
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break;
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}
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return NULL;
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}
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/**
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* lc_find - find element by label, if present in the hash table
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* @lc: The lru_cache object
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* @enr: element number
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*
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* Returns the pointer to an element, if the element with the requested
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* "label" or element number is present in the hash table,
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* or NULL if not found. Does not change the refcnt.
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* Ignores elements that are "about to be used", i.e. not yet in the active
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* set, but still pending transaction commit.
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*/
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struct lc_element *lc_find(struct lru_cache *lc, unsigned int enr)
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{
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return __lc_find(lc, enr, 0);
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}
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/**
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* lc_is_used - find element by label
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* @lc: The lru_cache object
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* @enr: element number
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*
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* Returns true, if the element with the requested "label" or element number is
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* present in the hash table, and is used (refcnt > 0).
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* Also finds elements that are not _currently_ used but only "about to be
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* used", i.e. on the "to_be_changed" list, pending transaction commit.
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*/
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bool lc_is_used(struct lru_cache *lc, unsigned int enr)
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{
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struct lc_element *e = __lc_find(lc, enr, 1);
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return e && e->refcnt;
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}
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/**
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* lc_del - removes an element from the cache
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* @lc: The lru_cache object
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* @e: The element to remove
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*
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* @e must be unused (refcnt == 0). Moves @e from "lru" to "free" list,
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* sets @e->enr to %LC_FREE.
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*/
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void lc_del(struct lru_cache *lc, struct lc_element *e)
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{
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PARANOIA_ENTRY();
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PARANOIA_LC_ELEMENT(lc, e);
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BUG_ON(e->refcnt);
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e->lc_number = e->lc_new_number = LC_FREE;
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hlist_del_init(&e->colision);
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list_move(&e->list, &lc->free);
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RETURN();
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}
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static struct lc_element *lc_prepare_for_change(struct lru_cache *lc, unsigned new_number)
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{
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struct list_head *n;
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struct lc_element *e;
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if (!list_empty(&lc->free))
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n = lc->free.next;
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else if (!list_empty(&lc->lru))
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n = lc->lru.prev;
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else
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return NULL;
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e = list_entry(n, struct lc_element, list);
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PARANOIA_LC_ELEMENT(lc, e);
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e->lc_new_number = new_number;
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if (!hlist_unhashed(&e->colision))
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__hlist_del(&e->colision);
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hlist_add_head(&e->colision, lc_hash_slot(lc, new_number));
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list_move(&e->list, &lc->to_be_changed);
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return e;
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}
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static int lc_unused_element_available(struct lru_cache *lc)
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{
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if (!list_empty(&lc->free))
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return 1; /* something on the free list */
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if (!list_empty(&lc->lru))
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return 1; /* something to evict */
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return 0;
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}
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/* used as internal flags to __lc_get */
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enum {
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LC_GET_MAY_CHANGE = 1,
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LC_GET_MAY_USE_UNCOMMITTED = 2,
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};
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static struct lc_element *__lc_get(struct lru_cache *lc, unsigned int enr, unsigned int flags)
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{
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struct lc_element *e;
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PARANOIA_ENTRY();
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if (lc->flags & LC_STARVING) {
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++lc->starving;
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RETURN(NULL);
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}
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e = __lc_find(lc, enr, 1);
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/* if lc_new_number != lc_number,
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* this enr is currently being pulled in already,
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* and will be available once the pending transaction
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* has been committed. */
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if (e) {
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if (e->lc_new_number != e->lc_number) {
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/* It has been found above, but on the "to_be_changed"
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* list, not yet committed. Don't pull it in twice,
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* wait for the transaction, then try again...
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*/
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if (!(flags & LC_GET_MAY_USE_UNCOMMITTED))
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RETURN(NULL);
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/* ... unless the caller is aware of the implications,
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* probably preparing a cumulative transaction. */
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++e->refcnt;
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++lc->hits;
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RETURN(e);
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}
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/* else: lc_new_number == lc_number; a real hit. */
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++lc->hits;
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if (e->refcnt++ == 0)
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lc->used++;
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list_move(&e->list, &lc->in_use); /* Not evictable... */
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RETURN(e);
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}
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/* e == NULL */
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++lc->misses;
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if (!(flags & LC_GET_MAY_CHANGE))
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RETURN(NULL);
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/* To avoid races with lc_try_lock(), first, mark us dirty
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* (using test_and_set_bit, as it implies memory barriers), ... */
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test_and_set_bit(__LC_DIRTY, &lc->flags);
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/* ... only then check if it is locked anyways. If lc_unlock clears
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* the dirty bit again, that's not a problem, we will come here again.
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*/
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if (test_bit(__LC_LOCKED, &lc->flags)) {
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++lc->locked;
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RETURN(NULL);
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}
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/* In case there is nothing available and we can not kick out
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* the LRU element, we have to wait ...
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*/
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if (!lc_unused_element_available(lc)) {
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__set_bit(__LC_STARVING, &lc->flags);
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RETURN(NULL);
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}
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/* It was not present in the active set. We are going to recycle an
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* unused (or even "free") element, but we won't accumulate more than
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* max_pending_changes changes. */
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if (lc->pending_changes >= lc->max_pending_changes)
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RETURN(NULL);
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e = lc_prepare_for_change(lc, enr);
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BUG_ON(!e);
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clear_bit(__LC_STARVING, &lc->flags);
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BUG_ON(++e->refcnt != 1);
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lc->used++;
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lc->pending_changes++;
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RETURN(e);
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}
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/**
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* lc_get - get element by label, maybe change the active set
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* @lc: the lru cache to operate on
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* @enr: the label to look up
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*
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* Finds an element in the cache, increases its usage count,
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* "touches" and returns it.
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*
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* In case the requested number is not present, it needs to be added to the
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* cache. Therefore it is possible that an other element becomes evicted from
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* the cache. In either case, the user is notified so he is able to e.g. keep
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* a persistent log of the cache changes, and therefore the objects in use.
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*
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* Return values:
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* NULL
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* The cache was marked %LC_STARVING,
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* or the requested label was not in the active set
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* and a changing transaction is still pending (@lc was marked %LC_DIRTY).
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* Or no unused or free element could be recycled (@lc will be marked as
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* %LC_STARVING, blocking further lc_get() operations).
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*
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* pointer to the element with the REQUESTED element number.
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* In this case, it can be used right away
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*
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* pointer to an UNUSED element with some different element number,
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* where that different number may also be %LC_FREE.
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*
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|
* In this case, the cache is marked %LC_DIRTY,
|
|
* so lc_try_lock() will no longer succeed.
|
|
* The returned element pointer is moved to the "to_be_changed" list,
|
|
* and registered with the new element number on the hash collision chains,
|
|
* so it is possible to pick it up from lc_is_used().
|
|
* Up to "max_pending_changes" (see lc_create()) can be accumulated.
|
|
* The user now should do whatever housekeeping is necessary,
|
|
* typically serialize on lc_try_lock_for_transaction(), then call
|
|
* lc_committed(lc) and lc_unlock(), 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)
|
|
{
|
|
return __lc_get(lc, enr, LC_GET_MAY_CHANGE);
|
|
}
|
|
|
|
/**
|
|
* lc_get_cumulative - like lc_get; also finds to-be-changed elements
|
|
* @lc: the lru cache to operate on
|
|
* @enr: the label to look up
|
|
*
|
|
* Unlike lc_get this also returns the element for @enr, if it is belonging to
|
|
* a pending transaction, so the return values are like for lc_get(),
|
|
* plus:
|
|
*
|
|
* pointer to an element already on the "to_be_changed" list.
|
|
* In this case, the cache was already marked %LC_DIRTY.
|
|
*
|
|
* Caller needs to make sure that the pending transaction is completed,
|
|
* before proceeding to actually use this element.
|
|
*/
|
|
struct lc_element *lc_get_cumulative(struct lru_cache *lc, unsigned int enr)
|
|
{
|
|
return __lc_get(lc, enr, LC_GET_MAY_CHANGE|LC_GET_MAY_USE_UNCOMMITTED);
|
|
}
|
|
|
|
/**
|
|
* lc_try_get - get element by label, if present; do not 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.
|
|
*
|
|
* Return values:
|
|
* NULL
|
|
* The cache was marked %LC_STARVING,
|
|
* or the requested label was not in the active set
|
|
*
|
|
* pointer to the element with the REQUESTED element number.
|
|
* In this case, it can be used right away
|
|
*/
|
|
struct lc_element *lc_try_get(struct lru_cache *lc, unsigned int enr)
|
|
{
|
|
return __lc_get(lc, enr, 0);
|
|
}
|
|
|
|
/**
|
|
* lc_committed - tell @lc that pending changes have been recorded
|
|
* @lc: the lru cache to operate on
|
|
*
|
|
* User is expected to serialize on explicit lc_try_lock_for_transaction()
|
|
* before the transaction is started, and later needs to lc_unlock() explicitly
|
|
* as well.
|
|
*/
|
|
void lc_committed(struct lru_cache *lc)
|
|
{
|
|
struct lc_element *e, *tmp;
|
|
|
|
PARANOIA_ENTRY();
|
|
list_for_each_entry_safe(e, tmp, &lc->to_be_changed, list) {
|
|
/* count number of changes, not number of transactions */
|
|
++lc->changed;
|
|
e->lc_number = e->lc_new_number;
|
|
list_move(&e->list, &lc->in_use);
|
|
}
|
|
lc->pending_changes = 0;
|
|
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_number != e->lc_new_number);
|
|
if (--e->refcnt == 0) {
|
|
/* move it to the front of LRU. */
|
|
list_move(&e->list, &lc->lru);
|
|
lc->used--;
|
|
clear_bit_unlock(__LC_STARVING, &lc->flags);
|
|
}
|
|
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;
|
|
struct list_head *lh;
|
|
|
|
if (index < 0 || index >= lc->nr_elements)
|
|
return;
|
|
|
|
e = lc_element_by_index(lc, index);
|
|
BUG_ON(e->lc_number != e->lc_new_number);
|
|
BUG_ON(e->refcnt != 0);
|
|
|
|
e->lc_number = e->lc_new_number = enr;
|
|
hlist_del_init(&e->colision);
|
|
if (enr == LC_FREE)
|
|
lh = &lc->free;
|
|
else {
|
|
hlist_add_head(&e->colision, lc_hash_slot(lc, enr));
|
|
lh = &lc->lru;
|
|
}
|
|
list_move(&e->list, lh);
|
|
}
|
|
|
|
/**
|
|
* 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 additional "heading" or other info
|
|
* @detail: function pointer the user may provide to dump further details
|
|
* of the object the lc_element is embedded in. May be NULL.
|
|
* Note: a leading space ' ' and trailing newline '\n' is implied.
|
|
*/
|
|
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 (new nr) refcnt %s\n ", utext);
|
|
for (i = 0; i < nr_elements; i++) {
|
|
e = lc_element_by_index(lc, i);
|
|
if (e->lc_number != e->lc_new_number)
|
|
seq_printf(seq, "\t%5d: %6d %8d %6d ",
|
|
i, e->lc_number, e->lc_new_number, e->refcnt);
|
|
else
|
|
seq_printf(seq, "\t%5d: %6d %-8s %6d ",
|
|
i, e->lc_number, "-\"-", e->refcnt);
|
|
if (detail)
|
|
detail(seq, e);
|
|
seq_putc(seq, '\n');
|
|
}
|
|
}
|
|
|
|
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_committed);
|
|
EXPORT_SYMBOL(lc_element_by_index);
|
|
EXPORT_SYMBOL(lc_index_of);
|
|
EXPORT_SYMBOL(lc_seq_printf_stats);
|
|
EXPORT_SYMBOL(lc_seq_dump_details);
|
|
EXPORT_SYMBOL(lc_try_lock);
|
|
EXPORT_SYMBOL(lc_is_used);
|
|
EXPORT_SYMBOL(lc_get_cumulative);
|