mm: cleancache: s/flush/invalidate/

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.

A "flush_page" will ensure the page no longer is present in cleancache;

a "flush_inode" will flush all pages associated with the specified file;

and, when a filesystem is unmounted, a "flush_fs" will flush all pages in

all files specified by the given pool id and also surrender the pool id.

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

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 flushed (thus

making cleancache an "exclusive" cache).  On a shared pool, the page

is NOT flushed on a successful get_page so that it remains accessible to

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 flush operations as required.

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

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 flushing a page

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.

succ_gets	- number of gets that were successful

failed_gets	- number of gets that failed

puts		- number of puts attempted (all "succeed")

flushes		- number of flushes attempted

invalidates	- number of invalidates attempted

A backend implementatation may provide additional metrics.

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_flush operations) between cleancache,

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

transcendent memory.

4) Why is non-shared cleancache "exclusive"?  And where is the

   page "flushed" after a "get"? (Minchan Kim)

   page "invalidated" after a "get"? (Minchan Kim)

The main reason is to free up space in transcendent memory and

to avoid unnecessary cleancache_flush calls.  If you want inclusive,

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_flush" call.

be easily extended to add a "get_no_invalidate" call.

The flush is done by the cleancache backend implementation.

The invalidate is done by the cleancache backend implementation.

5) What's the performance impact?

  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 "flush" operations

  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.

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 flushes the data page if the file

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

flushed the pages when the inode kva was freed, much of the value

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.

	/* 99% of the time, we don't need to flush the cleancache on the bdev.

	 * But, for the strange corners, lets be cautious

	 */

	cleancache_flush_inode(mapping);

	cleancache_invalidate_inode(mapping);

}

EXPORT_SYMBOL(invalidate_bdev);

{

	struct file_system_type *fs = s->s_type;

	if (atomic_dec_and_test(&s->s_active)) {

		cleancache_flush_fs(s);

		cleancache_invalidate_fs(s);

		fs->kill_sb(s);

		/* caches are now gone, we can safely kill the shrinker now */

			pgoff_t, struct page *);

	void (*put_page)(int, struct cleancache_filekey,

			pgoff_t, struct page *);

	/*

	 * NOTE: per akpm, flush_page, flush_inode and flush_fs will be

	 * renamed to invalidate_* in a later commit in which all

	 * dependencies (i.e Xen, zcache) will be renamed simultaneously

	 */

	void (*flush_page)(int, struct cleancache_filekey, pgoff_t);

	void (*flush_inode)(int, struct cleancache_filekey);

	void (*flush_fs)(int);

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 void __cleancache_invalidate_page(struct address_space *, struct page *);

extern void __cleancache_invalidate_inode(struct address_space *);

extern void __cleancache_invalidate_fs(struct super_block *);

extern int cleancache_enabled;

#ifdef CONFIG_CLEANCACHE

		__cleancache_put_page(page);

}

static inline void cleancache_flush_page(struct address_space *mapping,

static inline void cleancache_invalidate_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);

		__cleancache_invalidate_page(mapping, page);

}

static inline void cleancache_flush_inode(struct address_space *mapping)

static inline void cleancache_invalidate_inode(struct address_space *mapping)

{

	if (cleancache_enabled && cleancache_fs_enabled_mapping(mapping))

		__cleancache_flush_inode(mapping);

		__cleancache_invalidate_inode(mapping);

}

static inline void cleancache_flush_fs(struct super_block *sb)

static inline void cleancache_invalidate_fs(struct super_block *sb)

{

	if (cleancache_enabled)

		__cleancache_flush_fs(sb);

		__cleancache_invalidate_fs(sb);

}

#endif /* _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

 * by cleancache_get/put/invalidate 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.

EXPORT_SYMBOL(__cleancache_put_page);

/*

 * Flush any data from cleancache associated with the poolid and the

 * Invalidate 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)

void __cleancache_invalidate_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;

		}

	}

}

EXPORT_SYMBOL(__cleancache_flush_page);

EXPORT_SYMBOL(__cleancache_invalidate_page);

/*

 * Flush all data from cleancache associated with the poolid and the

 * Invalidate 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)

void __cleancache_invalidate_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);

EXPORT_SYMBOL(__cleancache_invalidate_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)

void __cleancache_invalidate_fs(struct super_block *sb)

{

	if (sb->cleancache_poolid >= 0) {

		int old_poolid = sb->cleancache_poolid;

		(*cleancache_ops.flush_fs)(old_poolid);

	}

}

EXPORT_SYMBOL(__cleancache_flush_fs);

EXPORT_SYMBOL(__cleancache_invalidate_fs);

#ifdef CONFIG_SYSFS