[PATCH v4 08/68] fscache: Implement cache registration
David Howells
dhowells at redhat.com
Wed Dec 22 15:15:48 PST 2021
Implement a register of caches and provide functions to manage it.
Two functions are provided for the cache backend to use:
(1) Acquire a cache cookie:
struct fscache_cache *fscache_acquire_cache(const char *name)
This gets the cache cookie for a cache of the specified name and moves
it to the preparation state. If a nameless cache cookie exists, that
will be given this name and used.
(2) Relinquish a cache cookie:
void fscache_relinquish_cache(struct fscache_cache *cache);
This relinquishes a cache cookie, cleans it and makes it available if
it's still referenced by a network filesystem.
Note that network filesystems don't deal with cache cookies directly, but
rather go straight to the volume registration.
Signed-off-by: David Howells <dhowells at redhat.com>
Reviewed-by: Jeff Layton <jlayton at kernel.org>
cc: linux-cachefs at redhat.com
Link: https://lore.kernel.org/r/163819587157.215744.13523139317322503286.stgit@warthog.procyon.org.uk/ # v1
Link: https://lore.kernel.org/r/163906889665.143852.10378009165231294456.stgit@warthog.procyon.org.uk/ # v2
Link: https://lore.kernel.org/r/163967085081.1823006.2218944206363626210.stgit@warthog.procyon.org.uk/ # v3
---
fs/fscache/Makefile | 1
fs/fscache/cache.c | 274 ++++++++++++++++++++++++++++++++++++++++
fs/fscache/internal.h | 33 +++++
fs/fscache/proc.c | 4 +
include/linux/fscache-cache.h | 34 +++++
include/trace/events/fscache.h | 43 ++++++
6 files changed, 389 insertions(+)
create mode 100644 fs/fscache/cache.c
diff --git a/fs/fscache/Makefile b/fs/fscache/Makefile
index f9722de32247..d9fc22c18090 100644
--- a/fs/fscache/Makefile
+++ b/fs/fscache/Makefile
@@ -4,6 +4,7 @@
#
fscache-y := \
+ cache.o \
main.o
fscache-$(CONFIG_PROC_FS) += proc.o
diff --git a/fs/fscache/cache.c b/fs/fscache/cache.c
new file mode 100644
index 000000000000..8db77bb9f8e2
--- /dev/null
+++ b/fs/fscache/cache.c
@@ -0,0 +1,274 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/* FS-Cache cache handling
+ *
+ * Copyright (C) 2021 Red Hat, Inc. All Rights Reserved.
+ * Written by David Howells (dhowells at redhat.com)
+ */
+
+#define FSCACHE_DEBUG_LEVEL CACHE
+#include <linux/export.h>
+#include <linux/slab.h>
+#include "internal.h"
+
+static LIST_HEAD(fscache_caches);
+DECLARE_RWSEM(fscache_addremove_sem);
+EXPORT_SYMBOL(fscache_addremove_sem);
+
+static atomic_t fscache_cache_debug_id;
+
+/*
+ * Allocate a cache cookie.
+ */
+static struct fscache_cache *fscache_alloc_cache(const char *name)
+{
+ struct fscache_cache *cache;
+
+ cache = kzalloc(sizeof(*cache), GFP_KERNEL);
+ if (cache) {
+ if (name) {
+ cache->name = kstrdup(name, GFP_KERNEL);
+ if (!cache->name) {
+ kfree(cache);
+ return NULL;
+ }
+ }
+ refcount_set(&cache->ref, 1);
+ INIT_LIST_HEAD(&cache->cache_link);
+ cache->debug_id = atomic_inc_return(&fscache_cache_debug_id);
+ }
+ return cache;
+}
+
+static bool fscache_get_cache_maybe(struct fscache_cache *cache,
+ enum fscache_cache_trace where)
+{
+ bool success;
+ int ref;
+
+ success = __refcount_inc_not_zero(&cache->ref, &ref);
+ if (success)
+ trace_fscache_cache(cache->debug_id, ref + 1, where);
+ return success;
+}
+
+/*
+ * Look up a cache cookie.
+ */
+struct fscache_cache *fscache_lookup_cache(const char *name, bool is_cache)
+{
+ struct fscache_cache *candidate, *cache, *unnamed = NULL;
+
+ /* firstly check for the existence of the cache under read lock */
+ down_read(&fscache_addremove_sem);
+
+ list_for_each_entry(cache, &fscache_caches, cache_link) {
+ if (cache->name && name && strcmp(cache->name, name) == 0 &&
+ fscache_get_cache_maybe(cache, fscache_cache_get_acquire))
+ goto got_cache_r;
+ if (!cache->name && !name &&
+ fscache_get_cache_maybe(cache, fscache_cache_get_acquire))
+ goto got_cache_r;
+ }
+
+ if (!name) {
+ list_for_each_entry(cache, &fscache_caches, cache_link) {
+ if (cache->name &&
+ fscache_get_cache_maybe(cache, fscache_cache_get_acquire))
+ goto got_cache_r;
+ }
+ }
+
+ up_read(&fscache_addremove_sem);
+
+ /* the cache does not exist - create a candidate */
+ candidate = fscache_alloc_cache(name);
+ if (!candidate)
+ return ERR_PTR(-ENOMEM);
+
+ /* write lock, search again and add if still not present */
+ down_write(&fscache_addremove_sem);
+
+ list_for_each_entry(cache, &fscache_caches, cache_link) {
+ if (cache->name && name && strcmp(cache->name, name) == 0 &&
+ fscache_get_cache_maybe(cache, fscache_cache_get_acquire))
+ goto got_cache_w;
+ if (!cache->name) {
+ unnamed = cache;
+ if (!name &&
+ fscache_get_cache_maybe(cache, fscache_cache_get_acquire))
+ goto got_cache_w;
+ }
+ }
+
+ if (unnamed && is_cache &&
+ fscache_get_cache_maybe(unnamed, fscache_cache_get_acquire))
+ goto use_unnamed_cache;
+
+ if (!name) {
+ list_for_each_entry(cache, &fscache_caches, cache_link) {
+ if (cache->name &&
+ fscache_get_cache_maybe(cache, fscache_cache_get_acquire))
+ goto got_cache_w;
+ }
+ }
+
+ list_add_tail(&candidate->cache_link, &fscache_caches);
+ trace_fscache_cache(candidate->debug_id,
+ refcount_read(&candidate->ref),
+ fscache_cache_new_acquire);
+ up_write(&fscache_addremove_sem);
+ return candidate;
+
+got_cache_r:
+ up_read(&fscache_addremove_sem);
+ return cache;
+use_unnamed_cache:
+ cache = unnamed;
+ cache->name = candidate->name;
+ candidate->name = NULL;
+got_cache_w:
+ up_write(&fscache_addremove_sem);
+ kfree(candidate->name);
+ kfree(candidate);
+ return cache;
+}
+
+/**
+ * fscache_acquire_cache - Acquire a cache-level cookie.
+ * @name: The name of the cache.
+ *
+ * Get a cookie to represent an actual cache. If a name is given and there is
+ * a nameless cache record available, this will acquire that and set its name,
+ * directing all the volumes using it to this cache.
+ *
+ * The cache will be switched over to the preparing state if not currently in
+ * use, otherwise -EBUSY will be returned.
+ */
+struct fscache_cache *fscache_acquire_cache(const char *name)
+{
+ struct fscache_cache *cache;
+
+ ASSERT(name);
+ cache = fscache_lookup_cache(name, true);
+ if (IS_ERR(cache))
+ return cache;
+
+ if (!fscache_set_cache_state_maybe(cache,
+ FSCACHE_CACHE_IS_NOT_PRESENT,
+ FSCACHE_CACHE_IS_PREPARING)) {
+ pr_warn("Cache tag %s in use\n", name);
+ fscache_put_cache(cache, fscache_cache_put_cache);
+ return ERR_PTR(-EBUSY);
+ }
+
+ return cache;
+}
+EXPORT_SYMBOL(fscache_acquire_cache);
+
+/**
+ * fscache_put_cache - Release a cache-level cookie.
+ * @cache: The cache cookie to be released
+ * @where: An indication of where the release happened
+ *
+ * Release the caller's reference on a cache-level cookie. The @where
+ * indication should give information about the circumstances in which the call
+ * occurs and will be logged through a tracepoint.
+ */
+void fscache_put_cache(struct fscache_cache *cache,
+ enum fscache_cache_trace where)
+{
+ unsigned int debug_id = cache->debug_id;
+ bool zero;
+ int ref;
+
+ if (IS_ERR_OR_NULL(cache))
+ return;
+
+ zero = __refcount_dec_and_test(&cache->ref, &ref);
+ trace_fscache_cache(debug_id, ref - 1, where);
+
+ if (zero) {
+ down_write(&fscache_addremove_sem);
+ list_del_init(&cache->cache_link);
+ up_write(&fscache_addremove_sem);
+ kfree(cache->name);
+ kfree(cache);
+ }
+}
+
+/**
+ * fscache_relinquish_cache - Reset cache state and release cookie
+ * @cache: The cache cookie to be released
+ *
+ * Reset the state of a cache and release the caller's reference on a cache
+ * cookie.
+ */
+void fscache_relinquish_cache(struct fscache_cache *cache)
+{
+ enum fscache_cache_trace where =
+ (cache->state == FSCACHE_CACHE_IS_PREPARING) ?
+ fscache_cache_put_prep_failed :
+ fscache_cache_put_relinquish;
+
+ cache->cache_priv = NULL;
+ smp_store_release(&cache->state, FSCACHE_CACHE_IS_NOT_PRESENT);
+ fscache_put_cache(cache, where);
+}
+EXPORT_SYMBOL(fscache_relinquish_cache);
+
+#ifdef CONFIG_PROC_FS
+static const char fscache_cache_states[NR__FSCACHE_CACHE_STATE] = "-PAEW";
+
+/*
+ * Generate a list of caches in /proc/fs/fscache/caches
+ */
+static int fscache_caches_seq_show(struct seq_file *m, void *v)
+{
+ struct fscache_cache *cache;
+
+ if (v == &fscache_caches) {
+ seq_puts(m,
+ "CACHE REF VOLS OBJS ACCES S NAME\n"
+ "======== ===== ===== ===== ===== = ===============\n"
+ );
+ return 0;
+ }
+
+ cache = list_entry(v, struct fscache_cache, cache_link);
+ seq_printf(m,
+ "%08x %5d %5d %5d %5d %c %s\n",
+ cache->debug_id,
+ refcount_read(&cache->ref),
+ atomic_read(&cache->n_volumes),
+ atomic_read(&cache->object_count),
+ atomic_read(&cache->n_accesses),
+ fscache_cache_states[cache->state],
+ cache->name ?: "-");
+ return 0;
+}
+
+static void *fscache_caches_seq_start(struct seq_file *m, loff_t *_pos)
+ __acquires(fscache_addremove_sem)
+{
+ down_read(&fscache_addremove_sem);
+ return seq_list_start_head(&fscache_caches, *_pos);
+}
+
+static void *fscache_caches_seq_next(struct seq_file *m, void *v, loff_t *_pos)
+{
+ return seq_list_next(v, &fscache_caches, _pos);
+}
+
+static void fscache_caches_seq_stop(struct seq_file *m, void *v)
+ __releases(fscache_addremove_sem)
+{
+ up_read(&fscache_addremove_sem);
+}
+
+const struct seq_operations fscache_caches_seq_ops = {
+ .start = fscache_caches_seq_start,
+ .next = fscache_caches_seq_next,
+ .stop = fscache_caches_seq_stop,
+ .show = fscache_caches_seq_show,
+};
+#endif /* CONFIG_PROC_FS */
diff --git a/fs/fscache/internal.h b/fs/fscache/internal.h
index f345bdb018ba..8fd39e7735fc 100644
--- a/fs/fscache/internal.h
+++ b/fs/fscache/internal.h
@@ -17,6 +17,39 @@
#include <linux/sched.h>
#include <linux/seq_file.h>
+/*
+ * cache.c
+ */
+#ifdef CONFIG_PROC_FS
+extern const struct seq_operations fscache_caches_seq_ops;
+#endif
+struct fscache_cache *fscache_lookup_cache(const char *name, bool is_cache);
+void fscache_put_cache(struct fscache_cache *cache, enum fscache_cache_trace where);
+
+static inline enum fscache_cache_state fscache_cache_state(const struct fscache_cache *cache)
+{
+ return smp_load_acquire(&cache->state);
+}
+
+static inline bool fscache_cache_is_live(const struct fscache_cache *cache)
+{
+ return fscache_cache_state(cache) == FSCACHE_CACHE_IS_ACTIVE;
+}
+
+static inline void fscache_set_cache_state(struct fscache_cache *cache,
+ enum fscache_cache_state new_state)
+{
+ smp_store_release(&cache->state, new_state);
+
+}
+
+static inline bool fscache_set_cache_state_maybe(struct fscache_cache *cache,
+ enum fscache_cache_state old_state,
+ enum fscache_cache_state new_state)
+{
+ return try_cmpxchg_release(&cache->state, &old_state, new_state);
+}
+
/*
* main.c
*/
diff --git a/fs/fscache/proc.c b/fs/fscache/proc.c
index 4d866ac41776..93b925709e09 100644
--- a/fs/fscache/proc.c
+++ b/fs/fscache/proc.c
@@ -19,6 +19,10 @@ int __init fscache_proc_init(void)
if (!proc_mkdir("fs/fscache", NULL))
goto error_dir;
+ if (!proc_create_seq("fs/fscache/caches", S_IFREG | 0444, NULL,
+ &fscache_caches_seq_ops))
+ goto error;
+
#ifdef CONFIG_FSCACHE_STATS
if (!proc_create_single("fs/fscache/stats", S_IFREG | 0444, NULL,
fscache_stats_show))
diff --git a/include/linux/fscache-cache.h b/include/linux/fscache-cache.h
index d6910a913918..18cd5c9877bb 100644
--- a/include/linux/fscache-cache.h
+++ b/include/linux/fscache-cache.h
@@ -16,6 +16,40 @@
#include <linux/fscache.h>
+enum fscache_cache_trace;
+enum fscache_access_trace;
+
+enum fscache_cache_state {
+ FSCACHE_CACHE_IS_NOT_PRESENT, /* No cache is present for this name */
+ FSCACHE_CACHE_IS_PREPARING, /* A cache is preparing to come live */
+ FSCACHE_CACHE_IS_ACTIVE, /* Attached cache is active and can be used */
+ FSCACHE_CACHE_GOT_IOERROR, /* Attached cache stopped on I/O error */
+ FSCACHE_CACHE_IS_WITHDRAWN, /* Attached cache is being withdrawn */
+#define NR__FSCACHE_CACHE_STATE (FSCACHE_CACHE_IS_WITHDRAWN + 1)
+};
+
+/*
+ * Cache cookie.
+ */
+struct fscache_cache {
+ struct list_head cache_link; /* Link in cache list */
+ void *cache_priv; /* Private cache data (or NULL) */
+ refcount_t ref;
+ atomic_t n_volumes; /* Number of active volumes; */
+ atomic_t n_accesses; /* Number of in-progress accesses on the cache */
+ atomic_t object_count; /* no. of live objects in this cache */
+ unsigned int debug_id;
+ enum fscache_cache_state state;
+ char *name;
+};
+
extern struct workqueue_struct *fscache_wq;
+/*
+ * out-of-line cache backend functions
+ */
+extern struct rw_semaphore fscache_addremove_sem;
+extern struct fscache_cache *fscache_acquire_cache(const char *name);
+extern void fscache_relinquish_cache(struct fscache_cache *cache);
+
#endif /* _LINUX_FSCACHE_CACHE_H */
diff --git a/include/trace/events/fscache.h b/include/trace/events/fscache.h
index fe214c5cc87f..3b8e0597b2c1 100644
--- a/include/trace/events/fscache.h
+++ b/include/trace/events/fscache.h
@@ -19,11 +19,27 @@
#ifndef __FSCACHE_DECLARE_TRACE_ENUMS_ONCE_ONLY
#define __FSCACHE_DECLARE_TRACE_ENUMS_ONCE_ONLY
+enum fscache_cache_trace {
+ fscache_cache_collision,
+ fscache_cache_get_acquire,
+ fscache_cache_new_acquire,
+ fscache_cache_put_cache,
+ fscache_cache_put_prep_failed,
+ fscache_cache_put_relinquish,
+};
+
#endif
/*
* Declare tracing information enums and their string mappings for display.
*/
+#define fscache_cache_traces \
+ EM(fscache_cache_collision, "*COLLIDE*") \
+ EM(fscache_cache_get_acquire, "GET acq ") \
+ EM(fscache_cache_new_acquire, "NEW acq ") \
+ EM(fscache_cache_put_cache, "PUT cache") \
+ EM(fscache_cache_put_prep_failed, "PUT pfail") \
+ E_(fscache_cache_put_relinquish, "PUT relnq")
/*
* Export enum symbols via userspace.
@@ -33,6 +49,8 @@
#define EM(a, b) TRACE_DEFINE_ENUM(a);
#define E_(a, b) TRACE_DEFINE_ENUM(a);
+fscache_cache_traces;
+
/*
* Now redefine the EM() and E_() macros to map the enums to the strings that
* will be printed in the output.
@@ -43,6 +61,31 @@
#define E_(a, b) { a, b }
+TRACE_EVENT(fscache_cache,
+ TP_PROTO(unsigned int cache_debug_id,
+ int usage,
+ enum fscache_cache_trace where),
+
+ TP_ARGS(cache_debug_id, usage, where),
+
+ TP_STRUCT__entry(
+ __field(unsigned int, cache )
+ __field(int, usage )
+ __field(enum fscache_cache_trace, where )
+ ),
+
+ TP_fast_assign(
+ __entry->cache = cache_debug_id;
+ __entry->usage = usage;
+ __entry->where = where;
+ ),
+
+ TP_printk("C=%08x %s r=%d",
+ __entry->cache,
+ __print_symbolic(__entry->where, fscache_cache_traces),
+ __entry->usage)
+ );
+
#endif /* _TRACE_FSCACHE_H */
/* This part must be outside protection */
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