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mm: cleancache core ops functions and config

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SecureCRT 2012-08-20 00:49:43 +08:00
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279
Documentation/vm/cleancache.txt Executable file
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MOTIVATION
Cleancache is a new optional feature provided by the VFS layer that
potentially dramatically increases page cache effectiveness for
many workloads in many environments at a negligible cost.
Cleancache can be thought of as a page-granularity victim cache for clean
pages that the kernel's pageframe replacement algorithm (PFRA) would like
to keep around, but can't since there isn't enough memory. So when the
PFRA "evicts" a page, it first attempts to use cleancache code to
put the data contained in that page into "transcendent memory", memory
that is not directly accessible or addressable by the kernel and is
of unknown and possibly time-varying size.
Later, when a cleancache-enabled filesystem wishes to access a page
in a file on disk, it first checks cleancache to see if it already
contains it; if it does, the page of data is copied into the kernel
and a disk access is avoided.
Transcendent memory "drivers" for cleancache are currently implemented
in Xen (using hypervisor memory) and zcache (using in-kernel compressed
memory) and other implementations are in development.
FAQs are included below.
IMPLEMENTATION OVERVIEW
A cleancache "backend" that provides transcendent memory registers itself
to the kernel's cleancache "frontend" by calling cleancache_register_ops,
passing a pointer to a cleancache_ops structure with funcs set appropriately.
Note that cleancache_register_ops returns the previous settings so that
chaining can be performed if desired. The functions provided must conform to
certain semantics as follows:
Most important, cleancache is "ephemeral". Pages which are copied into
cleancache have an indefinite lifetime which is completely unknowable
by the kernel and so may or may not still be in cleancache at any later time.
Thus, as its name implies, cleancache is not suitable for dirty pages.
Cleancache has complete discretion over what pages to preserve and what
pages to discard and when.
Mounting a cleancache-enabled filesystem should call "init_fs" to obtain a
pool id which, if positive, must be saved in the filesystem's superblock;
a negative return value indicates failure. A "put_page" will copy a
(presumably about-to-be-evicted) page into cleancache and associate it with
the pool id, a file key, and a page index into the file. (The combination
of a pool id, a file key, and an index is sometimes called a "handle".)
A "get_page" will copy the page, if found, from cleancache into kernel memory.
An "invalidate_page" will ensure the page no longer is present in cleancache;
an "invalidate_inode" will invalidate all pages associated with the specified
file; and, when a filesystem is unmounted, an "invalidate_fs" will invalidate
all pages in all files specified by the given pool id and also surrender
the pool id.
An "init_shared_fs", like init_fs, obtains a pool id but tells cleancache
to treat the pool as shared using a 128-bit UUID as a key. On systems
that may run multiple kernels (such as hard partitioned or virtualized
systems) that may share a clustered filesystem, and where cleancache
may be shared among those kernels, calls to init_shared_fs that specify the
same UUID will receive the same pool id, thus allowing the pages to
be shared. Note that any security requirements must be imposed outside
of the kernel (e.g. by "tools" that control cleancache). Or a
cleancache implementation can simply disable shared_init by always
returning a negative value.
If a get_page is successful on a non-shared pool, the page is invalidated
(thus making cleancache an "exclusive" cache). On a shared pool, the page
is NOT invalidated on a successful get_page so that it remains accessible to
other sharers. The kernel is responsible for ensuring coherency between
cleancache (shared or not), the page cache, and the filesystem, using
cleancache invalidate operations as required.
Note that cleancache must enforce put-put-get coherency and get-get
coherency. For the former, if two puts are made to the same handle but
with different data, say AAA by the first put and BBB by the second, a
subsequent get can never return the stale data (AAA). For get-get coherency,
if a get for a given handle fails, subsequent gets for that handle will
never succeed unless preceded by a successful put with that handle.
Last, cleancache provides no SMP serialization guarantees; if two
different Linux threads are simultaneously putting and invalidating a page
with the same handle, the results are indeterminate. Callers must
lock the page to ensure serial behavior.
CLEANCACHE PERFORMANCE METRICS
Cleancache monitoring is done by sysfs files in the
/sys/kernel/mm/cleancache directory. The effectiveness of cleancache
can be measured (across all filesystems) with:
succ_gets - number of gets that were successful
failed_gets - number of gets that failed
puts - number of puts attempted (all "succeed")
invalidates - number of invalidates attempted
A backend implementatation may provide additional metrics.
FAQ
1) Where's the value? (Andrew Morton)
Cleancache provides a significant performance benefit to many workloads
in many environments with negligible overhead by improving the
effectiveness of the pagecache. Clean pagecache pages are
saved in transcendent memory (RAM that is otherwise not directly
addressable to the kernel); fetching those pages later avoids "refaults"
and thus disk reads.
Cleancache (and its sister code "frontswap") provide interfaces for
this transcendent memory (aka "tmem"), which conceptually lies between
fast kernel-directly-addressable RAM and slower DMA/asynchronous devices.
Disallowing direct kernel or userland reads/writes to tmem
is ideal when data is transformed to a different form and size (such
as with compression) or secretly moved (as might be useful for write-
balancing for some RAM-like devices). Evicted page-cache pages (and
swap pages) are a great use for this kind of slower-than-RAM-but-much-
faster-than-disk transcendent memory, and the cleancache (and frontswap)
"page-object-oriented" specification provides a nice way to read and
write -- and indirectly "name" -- the pages.
In the virtual case, the whole point of virtualization is to statistically
multiplex physical resources across the varying demands of multiple
virtual machines. This is really hard to do with RAM and efforts to
do it well with no kernel change have essentially failed (except in some
well-publicized special-case workloads). Cleancache -- and frontswap --
with a fairly small impact on the kernel, provide a huge amount
of flexibility for more dynamic, flexible RAM multiplexing.
Specifically, the Xen Transcendent Memory backend allows otherwise
"fallow" hypervisor-owned RAM to not only be "time-shared" between multiple
virtual machines, but the pages can be compressed and deduplicated to
optimize RAM utilization. And when guest OS's are induced to surrender
underutilized RAM (e.g. with "self-ballooning"), page cache pages
are the first to go, and cleancache allows those pages to be
saved and reclaimed if overall host system memory conditions allow.
And the identical interface used for cleancache can be used in
physical systems as well. The zcache driver acts as a memory-hungry
device that stores pages of data in a compressed state. And
the proposed "RAMster" driver shares RAM across multiple physical
systems.
2) Why does cleancache have its sticky fingers so deep inside the
filesystems and VFS? (Andrew Morton and Christoph Hellwig)
The core hooks for cleancache in VFS are in most cases a single line
and the minimum set are placed precisely where needed to maintain
coherency (via cleancache_invalidate operations) between cleancache,
the page cache, and disk. All hooks compile into nothingness if
cleancache is config'ed off and turn into a function-pointer-
compare-to-NULL if config'ed on but no backend claims the ops
functions, or to a compare-struct-element-to-negative if a
backend claims the ops functions but a filesystem doesn't enable
cleancache.
Some filesystems are built entirely on top of VFS and the hooks
in VFS are sufficient, so don't require an "init_fs" hook; the
initial implementation of cleancache didn't provide this hook.
But for some filesystems (such as btrfs), the VFS hooks are
incomplete and one or more hooks in fs-specific code are required.
And for some other filesystems, such as tmpfs, cleancache may
be counterproductive. So it seemed prudent to require a filesystem
to "opt in" to use cleancache, which requires adding a hook in
each filesystem. Not all filesystems are supported by cleancache
only because they haven't been tested. The existing set should
be sufficient to validate the concept, the opt-in approach means
that untested filesystems are not affected, and the hooks in the
existing filesystems should make it very easy to add more
filesystems in the future.
The total impact of the hooks to existing fs and mm files is only
about 40 lines added (not counting comments and blank lines).
3) Why not make cleancache asynchronous and batched so it can
more easily interface with real devices with DMA instead
of copying each individual page? (Minchan Kim)
The one-page-at-a-time copy semantics simplifies the implementation
on both the frontend and backend and also allows the backend to
do fancy things on-the-fly like page compression and
page deduplication. And since the data is "gone" (copied into/out
of the pageframe) before the cleancache get/put call returns,
a great deal of race conditions and potential coherency issues
are avoided. While the interface seems odd for a "real device"
or for real kernel-addressable RAM, it makes perfect sense for
transcendent memory.
4) Why is non-shared cleancache "exclusive"? And where is the
page "invalidated" after a "get"? (Minchan Kim)
The main reason is to free up space in transcendent memory and
to avoid unnecessary cleancache_invalidate calls. If you want inclusive,
the page can be "put" immediately following the "get". If
put-after-get for inclusive becomes common, the interface could
be easily extended to add a "get_no_invalidate" call.
The invalidate is done by the cleancache backend implementation.
5) What's the performance impact?
Performance analysis has been presented at OLS'09 and LCA'10.
Briefly, performance gains can be significant on most workloads,
especially when memory pressure is high (e.g. when RAM is
overcommitted in a virtual workload); and because the hooks are
invoked primarily in place of or in addition to a disk read/write,
overhead is negligible even in worst case workloads. Basically
cleancache replaces I/O with memory-copy-CPU-overhead; on older
single-core systems with slow memory-copy speeds, cleancache
has little value, but in newer multicore machines, especially
consolidated/virtualized machines, it has great value.
6) How do I add cleancache support for filesystem X? (Boaz Harrash)
Filesystems that are well-behaved and conform to certain
restrictions can utilize cleancache simply by making a call to
cleancache_init_fs at mount time. Unusual, misbehaving, or
poorly layered filesystems must either add additional hooks
and/or undergo extensive additional testing... or should just
not enable the optional cleancache.
Some points for a filesystem to consider:
- The FS should be block-device-based (e.g. a ram-based FS such
as tmpfs should not enable cleancache)
- To ensure coherency/correctness, the FS must ensure that all
file removal or truncation operations either go through VFS or
add hooks to do the equivalent cleancache "invalidate" operations
- To ensure coherency/correctness, either inode numbers must
be unique across the lifetime of the on-disk file OR the
FS must provide an "encode_fh" function.
- The FS must call the VFS superblock alloc and deactivate routines
or add hooks to do the equivalent cleancache calls done there.
- To maximize performance, all pages fetched from the FS should
go through the do_mpag_readpage routine or the FS should add
hooks to do the equivalent (cf. btrfs)
- Currently, the FS blocksize must be the same as PAGESIZE. This
is not an architectural restriction, but no backends currently
support anything different.
- A clustered FS should invoke the "shared_init_fs" cleancache
hook to get best performance for some backends.
7) Why not use the KVA of the inode as the key? (Christoph Hellwig)
If cleancache would use the inode virtual address instead of
inode/filehandle, the pool id could be eliminated. But, this
won't work because cleancache retains pagecache data pages
persistently even when the inode has been pruned from the
inode unused list, and only invalidates the data page if the file
gets removed/truncated. So if cleancache used the inode kva,
there would be potential coherency issues if/when the inode
kva is reused for a different file. Alternately, if cleancache
invalidated the pages when the inode kva was freed, much of the value
of cleancache would be lost because the cache of pages in cleanache
is potentially much larger than the kernel pagecache and is most
useful if the pages survive inode cache removal.
8) Why is a global variable required?
The cleancache_enabled flag is checked in all of the frequently-used
cleancache hooks. The alternative is a function call to check a static
variable. Since cleancache is enabled dynamically at runtime, systems
that don't enable cleancache would suffer thousands (possibly
tens-of-thousands) of unnecessary function calls per second. So the
global variable allows cleancache to be enabled by default at compile
time, but have insignificant performance impact when cleancache remains
disabled at runtime.
9) Does cleanache work with KVM?
The memory model of KVM is sufficiently different that a cleancache
backend may have less value for KVM. This remains to be tested,
especially in an overcommitted system.
10) Does cleancache work in userspace? It sounds useful for
memory hungry caches like web browsers. (Jamie Lokier)
No plans yet, though we agree it sounds useful, at least for
apps that bypass the page cache (e.g. O_DIRECT).
Last updated: Dan Magenheimer, April 13 2011

122
include/linux/cleancache.h Executable file
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#ifndef _LINUX_CLEANCACHE_H
#define _LINUX_CLEANCACHE_H
#include <linux/fs.h>
#include <linux/exportfs.h>
#include <linux/mm.h>
#define CLEANCACHE_KEY_MAX 6
/*
* cleancache requires every file with a page in cleancache to have a
* unique key unless/until the file is removed/truncated. For some
* filesystems, the inode number is unique, but for "modern" filesystems
* an exportable filehandle is required (see exportfs.h)
*/
struct cleancache_filekey {
union {
ino_t ino;
__u32 fh[CLEANCACHE_KEY_MAX];
u32 key[CLEANCACHE_KEY_MAX];
} u;
};
struct cleancache_ops {
int (*init_fs)(size_t);
int (*init_shared_fs)(char *uuid, size_t);
int (*get_page)(int, struct cleancache_filekey,
pgoff_t, struct page *);
void (*put_page)(int, struct cleancache_filekey,
pgoff_t, struct page *);
void (*flush_page)(int, struct cleancache_filekey, pgoff_t);
void (*flush_inode)(int, struct cleancache_filekey);
void (*flush_fs)(int);
};
extern struct cleancache_ops
cleancache_register_ops(struct cleancache_ops *ops);
extern void __cleancache_init_fs(struct super_block *);
extern void __cleancache_init_shared_fs(char *, struct super_block *);
extern int __cleancache_get_page(struct page *);
extern void __cleancache_put_page(struct page *);
extern void __cleancache_flush_page(struct address_space *, struct page *);
extern void __cleancache_flush_inode(struct address_space *);
extern void __cleancache_flush_fs(struct super_block *);
extern int cleancache_enabled;
#ifdef CONFIG_CLEANCACHE
static inline bool cleancache_fs_enabled(struct page *page)
{
return page->mapping->host->i_sb->cleancache_poolid >= 0;
}
static inline bool cleancache_fs_enabled_mapping(struct address_space *mapping)
{
return mapping->host->i_sb->cleancache_poolid >= 0;
}
#else
#define cleancache_enabled (0)
#define cleancache_fs_enabled(_page) (0)
#define cleancache_fs_enabled_mapping(_page) (0)
#endif
/*
* The shim layer provided by these inline functions allows the compiler
* to reduce all cleancache hooks to nothingness if CONFIG_CLEANCACHE
* is disabled, to a single global variable check if CONFIG_CLEANCACHE
* is enabled but no cleancache "backend" has dynamically enabled it,
* and, for the most frequent cleancache ops, to a single global variable
* check plus a superblock element comparison if CONFIG_CLEANCACHE is enabled
* and a cleancache backend has dynamically enabled cleancache, but the
* filesystem referenced by that cleancache op has not enabled cleancache.
* As a result, CONFIG_CLEANCACHE can be enabled by default with essentially
* no measurable performance impact.
*/
static inline void cleancache_init_fs(struct super_block *sb)
{
if (cleancache_enabled)
__cleancache_init_fs(sb);
}
static inline void cleancache_init_shared_fs(char *uuid, struct super_block *sb)
{
if (cleancache_enabled)
__cleancache_init_shared_fs(uuid, sb);
}
static inline int cleancache_get_page(struct page *page)
{
int ret = -1;
if (cleancache_enabled && cleancache_fs_enabled(page))
ret = __cleancache_get_page(page);
return ret;
}
static inline void cleancache_put_page(struct page *page)
{
if (cleancache_enabled && cleancache_fs_enabled(page))
__cleancache_put_page(page);
}
static inline void cleancache_flush_page(struct address_space *mapping,
struct page *page)
{
/* careful... page->mapping is NULL sometimes when this is called */
if (cleancache_enabled && cleancache_fs_enabled_mapping(mapping))
__cleancache_flush_page(mapping, page);
}
static inline void cleancache_flush_inode(struct address_space *mapping)
{
if (cleancache_enabled && cleancache_fs_enabled_mapping(mapping))
__cleancache_flush_inode(mapping);
}
static inline void cleancache_flush_fs(struct super_block *sb)
{
if (cleancache_enabled)
__cleancache_flush_fs(sb);
}
#endif /* _LINUX_CLEANCACHE_H */

22
mm/Kconfig Normal file → Executable file
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@ -288,3 +288,25 @@ config NOMMU_INITIAL_TRIM_EXCESS
of 1 says that all excess pages should be trimmed.
See Documentation/nommu-mmap.txt for more information.
config CLEANCACHE
bool "Enable cleancache driver to cache clean pages if tmem is present"
default n
help
Cleancache can be thought of as a page-granularity victim cache
for clean pages that the kernel's pageframe replacement algorithm
(PFRA) would like to keep around, but can't since there isn't enough
memory. So when the PFRA "evicts" a page, it first attempts to use
cleancacne code to put the data contained in that page into
"transcendent memory", memory that is not directly accessible or
addressable by the kernel and is of unknown and possibly
time-varying size. And when a cleancache-enabled
filesystem wishes to access a page in a file on disk, it first
checks cleancache to see if it already contains it; if it does,
the page is copied into the kernel and a disk access is avoided.
When a transcendent memory driver is available (such as zcache or
Xen transcendent memory), a significant I/O reduction
may be achieved. When none is available, all cleancache calls
are reduced to a single pointer-compare-against-NULL resulting
in a negligible performance hit.
If unsure, say Y to enable cleancache

1
mm/Makefile Normal file → Executable file
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@ -46,3 +46,4 @@ obj-$(CONFIG_MEMORY_FAILURE) += memory-failure.o
obj-$(CONFIG_HWPOISON_INJECT) += hwpoison-inject.o
obj-$(CONFIG_DEBUG_KMEMLEAK) += kmemleak.o
obj-$(CONFIG_DEBUG_KMEMLEAK_TEST) += kmemleak-test.o
obj-$(CONFIG_CLEANCACHE) += cleancache.o

244
mm/cleancache.c Executable file
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/*
* Cleancache frontend
*
* This code provides the generic "frontend" layer to call a matching
* "backend" driver implementation of cleancache. See
* Documentation/vm/cleancache.txt for more information.
*
* Copyright (C) 2009-2010 Oracle Corp. All rights reserved.
* Author: Dan Magenheimer
*
* This work is licensed under the terms of the GNU GPL, version 2.
*/
#include <linux/module.h>
#include <linux/fs.h>
#include <linux/exportfs.h>
#include <linux/mm.h>
#include <linux/cleancache.h>
/*
* This global enablement flag may be read thousands of times per second
* by cleancache_get/put/flush even on systems where cleancache_ops
* is not claimed (e.g. cleancache is config'ed on but remains
* disabled), so is preferred to the slower alternative: a function
* call that checks a non-global.
*/
int cleancache_enabled;
EXPORT_SYMBOL(cleancache_enabled);
/*
* cleancache_ops is set by cleancache_ops_register to contain the pointers
* to the cleancache "backend" implementation functions.
*/
static struct cleancache_ops cleancache_ops;
/* useful stats available in /sys/kernel/mm/cleancache */
static unsigned long cleancache_succ_gets;
static unsigned long cleancache_failed_gets;
static unsigned long cleancache_puts;
static unsigned long cleancache_flushes;
/*
* register operations for cleancache, returning previous thus allowing
* detection of multiple backends and possible nesting
*/
struct cleancache_ops cleancache_register_ops(struct cleancache_ops *ops)
{
struct cleancache_ops old = cleancache_ops;
cleancache_ops = *ops;
cleancache_enabled = 1;
return old;
}
EXPORT_SYMBOL(cleancache_register_ops);
/* Called by a cleancache-enabled filesystem at time of mount */
void __cleancache_init_fs(struct super_block *sb)
{
sb->cleancache_poolid = (*cleancache_ops.init_fs)(PAGE_SIZE);
}
EXPORT_SYMBOL(__cleancache_init_fs);
/* Called by a cleancache-enabled clustered filesystem at time of mount */
void __cleancache_init_shared_fs(char *uuid, struct super_block *sb)
{
sb->cleancache_poolid =
(*cleancache_ops.init_shared_fs)(uuid, PAGE_SIZE);
}
EXPORT_SYMBOL(__cleancache_init_shared_fs);
/*
* If the filesystem uses exportable filehandles, use the filehandle as
* the key, else use the inode number.
*/
static int cleancache_get_key(struct inode *inode,
struct cleancache_filekey *key)
{
int (*fhfn)(struct dentry *, __u32 *fh, int *, int);
int len = 0, maxlen = CLEANCACHE_KEY_MAX;
struct super_block *sb = inode->i_sb;
key->u.ino = inode->i_ino;
if (sb->s_export_op != NULL) {
fhfn = sb->s_export_op->encode_fh;
if (fhfn) {
struct dentry d;
d.d_inode = inode;
len = (*fhfn)(&d, &key->u.fh[0], &maxlen, 0);
if (len <= 0 || len == 255)
return -1;
if (maxlen > CLEANCACHE_KEY_MAX)
return -1;
}
}
return 0;
}
/*
* "Get" data from cleancache associated with the poolid/inode/index
* that were specified when the data was put to cleanache and, if
* successful, use it to fill the specified page with data and return 0.
* The pageframe is unchanged and returns -1 if the get fails.
* Page must be locked by caller.
*/
int __cleancache_get_page(struct page *page)
{
int ret = -1;
int pool_id;
struct cleancache_filekey key = { .u.key = { 0 } };
VM_BUG_ON(!PageLocked(page));
pool_id = page->mapping->host->i_sb->cleancache_poolid;
if (pool_id < 0)
goto out;
if (cleancache_get_key(page->mapping->host, &key) < 0)
goto out;
ret = (*cleancache_ops.get_page)(pool_id, key, page->index, page);
if (ret == 0)
cleancache_succ_gets++;
else
cleancache_failed_gets++;
out:
return ret;
}
EXPORT_SYMBOL(__cleancache_get_page);
/*
* "Put" data from a page to cleancache and associate it with the
* (previously-obtained per-filesystem) poolid and the page's,
* inode and page index. Page must be locked. Note that a put_page
* always "succeeds", though a subsequent get_page may succeed or fail.
*/
void __cleancache_put_page(struct page *page)
{
int pool_id;
struct cleancache_filekey key = { .u.key = { 0 } };
VM_BUG_ON(!PageLocked(page));
pool_id = page->mapping->host->i_sb->cleancache_poolid;
if (pool_id >= 0 &&
cleancache_get_key(page->mapping->host, &key) >= 0) {
(*cleancache_ops.put_page)(pool_id, key, page->index, page);
cleancache_puts++;
}
}
EXPORT_SYMBOL(__cleancache_put_page);
/*
* Flush any data from cleancache associated with the poolid and the
* page's inode and page index so that a subsequent "get" will fail.
*/
void __cleancache_flush_page(struct address_space *mapping, struct page *page)
{
/* careful... page->mapping is NULL sometimes when this is called */
int pool_id = mapping->host->i_sb->cleancache_poolid;
struct cleancache_filekey key = { .u.key = { 0 } };
if (pool_id >= 0) {
VM_BUG_ON(!PageLocked(page));
if (cleancache_get_key(mapping->host, &key) >= 0) {
(*cleancache_ops.flush_page)(pool_id, key, page->index);
cleancache_flushes++;
}
}
}
EXPORT_SYMBOL(__cleancache_flush_page);
/*
* Flush all data from cleancache associated with the poolid and the
* mappings's inode so that all subsequent gets to this poolid/inode
* will fail.
*/
void __cleancache_flush_inode(struct address_space *mapping)
{
int pool_id = mapping->host->i_sb->cleancache_poolid;
struct cleancache_filekey key = { .u.key = { 0 } };
if (pool_id >= 0 && cleancache_get_key(mapping->host, &key) >= 0)
(*cleancache_ops.flush_inode)(pool_id, key);
}
EXPORT_SYMBOL(__cleancache_flush_inode);
/*
* Called by any cleancache-enabled filesystem at time of unmount;
* note that pool_id is surrendered and may be reutrned by a subsequent
* cleancache_init_fs or cleancache_init_shared_fs
*/
void __cleancache_flush_fs(struct super_block *sb)
{
if (sb->cleancache_poolid >= 0) {
int old_poolid = sb->cleancache_poolid;
sb->cleancache_poolid = -1;
(*cleancache_ops.flush_fs)(old_poolid);
}
}
EXPORT_SYMBOL(__cleancache_flush_fs);
#ifdef CONFIG_SYSFS
/* see Documentation/ABI/xxx/sysfs-kernel-mm-cleancache */
#define CLEANCACHE_SYSFS_RO(_name) \
static ssize_t cleancache_##_name##_show(struct kobject *kobj, \
struct kobj_attribute *attr, char *buf) \
{ \
return sprintf(buf, "%lu\n", cleancache_##_name); \
} \
static struct kobj_attribute cleancache_##_name##_attr = { \
.attr = { .name = __stringify(_name), .mode = 0444 }, \
.show = cleancache_##_name##_show, \
}
CLEANCACHE_SYSFS_RO(succ_gets);
CLEANCACHE_SYSFS_RO(failed_gets);
CLEANCACHE_SYSFS_RO(puts);
CLEANCACHE_SYSFS_RO(flushes);
static struct attribute *cleancache_attrs[] = {
&cleancache_succ_gets_attr.attr,
&cleancache_failed_gets_attr.attr,
&cleancache_puts_attr.attr,
&cleancache_flushes_attr.attr,
NULL,
};
static struct attribute_group cleancache_attr_group = {
.attrs = cleancache_attrs,
.name = "cleancache",
};
#endif /* CONFIG_SYSFS */
static int __init init_cleancache(void)
{
#ifdef CONFIG_SYSFS
int err;
err = sysfs_create_group(mm_kobj, &cleancache_attr_group);
#endif /* CONFIG_SYSFS */
return 0;
}
module_init(init_cleancache)