forked from Minki/linux
a7733fb632
Add a number of helper functions to manage access to a cookie, pinning the
cache object in place for the duration to prevent cache withdrawal from
removing it:
(1) void fscache_init_access_gate(struct fscache_cookie *cookie);
This function initialises the access count when a cache binds to a
cookie. An extra ref is taken on the access count to prevent wakeups
while the cache is active. We're only interested in the wakeup when a
cookie is being withdrawn and we're waiting for it to quiesce - at
which point the counter will be decremented before the wait.
The FSCACHE_COOKIE_NACC_ELEVATED flag is set on the cookie to keep
track of the extra ref in order to handle a race between
relinquishment and withdrawal both trying to drop the extra ref.
(2) bool fscache_begin_cookie_access(struct fscache_cookie *cookie,
enum fscache_access_trace why);
This function attempts to begin access upon a cookie, pinning it in
place if it's cached. If successful, it returns true and leaves a the
access count incremented.
(3) void fscache_end_cookie_access(struct fscache_cookie *cookie,
enum fscache_access_trace why);
This function drops the access count obtained by (2), permitting
object withdrawal to take place when it reaches zero.
A tracepoint is provided to track changes to the access counter on a
cookie.
Changes
=======
ver #2:
- Don't hold n_accesses elevated whilst cache is bound to a cookie, but
rather add a flag that prevents the state machine from being queued when
n_accesses reaches 0.
Signed-off-by: David Howells <dhowells@redhat.com>
Reviewed-by: Jeff Layton <jlayton@kernel.org>
cc: linux-cachefs@redhat.com
Link: https://lore.kernel.org/r/163819595085.215744.1706073049250505427.stgit@warthog.procyon.org.uk/ # v1
Link: https://lore.kernel.org/r/163906895313.143852.10141619544149102193.stgit@warthog.procyon.org.uk/ # v2
Link: https://lore.kernel.org/r/163967095980.1823006.1133648159424418877.stgit@warthog.procyon.org.uk/ # v3
Link: https://lore.kernel.org/r/164021503063.640689.8870918985269528670.stgit@warthog.procyon.org.uk/ # v4
122 lines
2.8 KiB
C
122 lines
2.8 KiB
C
// SPDX-License-Identifier: GPL-2.0-or-later
|
|
/* General filesystem local caching manager
|
|
*
|
|
* Copyright (C) 2021 Red Hat, Inc. All Rights Reserved.
|
|
* Written by David Howells (dhowells@redhat.com)
|
|
*/
|
|
|
|
#define FSCACHE_DEBUG_LEVEL CACHE
|
|
#include <linux/module.h>
|
|
#include <linux/init.h>
|
|
#define CREATE_TRACE_POINTS
|
|
#include "internal.h"
|
|
|
|
MODULE_DESCRIPTION("FS Cache Manager");
|
|
MODULE_AUTHOR("Red Hat, Inc.");
|
|
MODULE_LICENSE("GPL");
|
|
|
|
unsigned fscache_debug;
|
|
module_param_named(debug, fscache_debug, uint,
|
|
S_IWUSR | S_IRUGO);
|
|
MODULE_PARM_DESC(fscache_debug,
|
|
"FS-Cache debugging mask");
|
|
|
|
EXPORT_TRACEPOINT_SYMBOL(fscache_access_cache);
|
|
EXPORT_TRACEPOINT_SYMBOL(fscache_access_volume);
|
|
EXPORT_TRACEPOINT_SYMBOL(fscache_access);
|
|
|
|
struct workqueue_struct *fscache_wq;
|
|
EXPORT_SYMBOL(fscache_wq);
|
|
|
|
/*
|
|
* Mixing scores (in bits) for (7,20):
|
|
* Input delta: 1-bit 2-bit
|
|
* 1 round: 330.3 9201.6
|
|
* 2 rounds: 1246.4 25475.4
|
|
* 3 rounds: 1907.1 31295.1
|
|
* 4 rounds: 2042.3 31718.6
|
|
* Perfect: 2048 31744
|
|
* (32*64) (32*31/2 * 64)
|
|
*/
|
|
#define HASH_MIX(x, y, a) \
|
|
( x ^= (a), \
|
|
y ^= x, x = rol32(x, 7),\
|
|
x += y, y = rol32(y,20),\
|
|
y *= 9 )
|
|
|
|
static inline unsigned int fold_hash(unsigned long x, unsigned long y)
|
|
{
|
|
/* Use arch-optimized multiply if one exists */
|
|
return __hash_32(y ^ __hash_32(x));
|
|
}
|
|
|
|
/*
|
|
* Generate a hash. This is derived from full_name_hash(), but we want to be
|
|
* sure it is arch independent and that it doesn't change as bits of the
|
|
* computed hash value might appear on disk. The caller must guarantee that
|
|
* the source data is a multiple of four bytes in size.
|
|
*/
|
|
unsigned int fscache_hash(unsigned int salt, const void *data, size_t len)
|
|
{
|
|
const __le32 *p = data;
|
|
unsigned int a, x = 0, y = salt, n = len / sizeof(__le32);
|
|
|
|
for (; n; n--) {
|
|
a = le32_to_cpu(*p++);
|
|
HASH_MIX(x, y, a);
|
|
}
|
|
return fold_hash(x, y);
|
|
}
|
|
|
|
/*
|
|
* initialise the fs caching module
|
|
*/
|
|
static int __init fscache_init(void)
|
|
{
|
|
int ret = -ENOMEM;
|
|
|
|
fscache_wq = alloc_workqueue("fscache", WQ_UNBOUND | WQ_FREEZABLE, 0);
|
|
if (!fscache_wq)
|
|
goto error_wq;
|
|
|
|
ret = fscache_proc_init();
|
|
if (ret < 0)
|
|
goto error_proc;
|
|
|
|
fscache_cookie_jar = kmem_cache_create("fscache_cookie_jar",
|
|
sizeof(struct fscache_cookie),
|
|
0, 0, NULL);
|
|
if (!fscache_cookie_jar) {
|
|
pr_notice("Failed to allocate a cookie jar\n");
|
|
ret = -ENOMEM;
|
|
goto error_cookie_jar;
|
|
}
|
|
|
|
pr_notice("Loaded\n");
|
|
return 0;
|
|
|
|
error_cookie_jar:
|
|
fscache_proc_cleanup();
|
|
error_proc:
|
|
destroy_workqueue(fscache_wq);
|
|
error_wq:
|
|
return ret;
|
|
}
|
|
|
|
fs_initcall(fscache_init);
|
|
|
|
/*
|
|
* clean up on module removal
|
|
*/
|
|
static void __exit fscache_exit(void)
|
|
{
|
|
_enter("");
|
|
|
|
kmem_cache_destroy(fscache_cookie_jar);
|
|
fscache_proc_cleanup();
|
|
destroy_workqueue(fscache_wq);
|
|
pr_notice("Unloaded\n");
|
|
}
|
|
|
|
module_exit(fscache_exit);
|