Re: [PATCH V4 3/8] Cleancache: core ops functions and configuration

[Jeremy Fitzhardinge]

 On 08/30/2010 03:31 PM, Dan Magenheimer wrote:
> [PATCH V4 3/8] Cleancache: core ops functions and configuration
>
> Cleancache core ops functions and configuration
>
> Credits: Cleancache_ops design derived from Jeremy Fitzhardinge
> design for tmem; sysfs code modelled after mm/ksm.c
>
> Note that CONFIG_CLEANCACHE defaults to on; all hooks devolve
> to a compare-function-pointer-to-NULL so performance impact should
> be negligible, but can be reduced to zero impact if config'ed off.
>
> Signed-off-by: Dan Magenheimer <dan.magenheimer@xxxxxxxxxx>
>
> Diffstat:
>  include/linux/cleancache.h               |  101 ++++++++++
>  mm/Kconfig                               |   22 ++
>  mm/Makefile                              |    1 
>  mm/cleancache.c                          |  201 +++++++++++++++++++++
>  4 files changed, 325 insertions(+)
>
> --- linux-2.6.36-rc3/include/linux/cleancache.h	1969-12-31 17:00:00.000000000 -0700
> +++ linux-2.6.36-rc3-cleancache/include/linux/cleancache.h	2010-08-30 14:54:31.000000000 -0600
> @@ -0,0 +1,101 @@
> +#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
> +
> +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_ops;
> +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 *);
> +
> +#ifdef CONFIG_CLEANCACHE
> +#define cleancache_enabled (cleancache_ops.init_fs)

Pointers can be used in a boolean context, but it would probably be
cleaner to have this evaluate to a proper boolean type.  Also I'd
probably go with an all-caps macro name rather than making it look like
a variable.

> +#else
> +#define cleancache_enabled (0)
> +#endif
> +
> +/* called by a cleancache-enabled filesystem at time of mount */
> +static inline int cleancache_init_fs(size_t pagesize)
> +{
> +	int ret = -1;
> +
> +	if (cleancache_enabled)
> +		ret = (*cleancache_ops.init_fs)(pagesize);
> +	return ret;
> +}
> +
> +/* called by a cleancache-enabled clustered filesystem at time of mount */
> +static inline int cleancache_init_shared_fs(char *uuid, size_t pagesize)
> +{
> +	int ret = -1;
> +
> +	if (cleancache_enabled)
> +		ret = (*cleancache_ops.init_shared_fs)(uuid, pagesize);
> +	return ret;
> +}
> +
> +static inline int cleancache_get_page(struct page *page)
> +{
> +	int ret = -1;
> +
> +	if (cleancache_enabled)
> +		ret = __cleancache_get_page(page);
> +	return ret;
> +}
> +
> +static inline void cleancache_put_page(struct page *page)
> +{
> +	if (cleancache_enabled)
> +		__cleancache_put_page(page);
> +}
> +
> +static inline void cleancache_flush_page(struct address_space *mapping,
> +					struct page *page)
> +{
> +	if (cleancache_enabled)
> +		__cleancache_flush_page(mapping, page);
> +}
> +
> +static inline void cleancache_flush_inode(struct address_space *mapping)
> +{
> +	if (cleancache_enabled)
> +		__cleancache_flush_inode(mapping);
> +}
> +
> +/*
> + * called by any cleancache-enabled filesystem at time of unmount;
> + * note that pool_id is surrendered and may be returned by a subsequent
> + * cleancache_init_fs or cleancache_init_shared_fs
> + */
> +static inline void cleancache_flush_fs(int pool_id)
> +{
> +	if (cleancache_enabled && pool_id >= 0)
> +		(*cleancache_ops.flush_fs)(pool_id);
> +}
> +
> +#endif /* _LINUX_CLEANCACHE_H */
> --- linux-2.6.36-rc3/mm/cleancache.c	1969-12-31 17:00:00.000000000 -0700
> +++ linux-2.6.36-rc3-cleancache/mm/cleancache.c	2010-08-30 14:58:40.000000000 -0600
> @@ -0,0 +1,201 @@
> +/*
> + * 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>
> +
> +/*
> + * cleancache_ops contains the pointers to the cleancache "backend"
> + * implementation functions.  This global variable may be checked thousands
> + * of times per second by cleancache_get/put/flush_page even on systems
> + * where cleancache_ops is not claimed (e.g. cleancache stays disabled),
> + * so is preferred to the slower alternative: a function call that
> + * checks a non-global.
> + */
> +struct cleancache_ops cleancache_ops;
> +
> +/* useful stats available in /sys/kernel/mm/cleancache */
> +static unsigned long succ_gets;
> +static unsigned long failed_gets;
> +static unsigned long puts;
> +static unsigned long flushes;

I'd probably give these very generic-sounding names some slightly unique
prefix just to help out people looking at "nm" output or using ctags.

> +
> +/*
> + * If the filesystem uses exportable filehandles, use the filehandle as
> + * the key, else use the inode number.
> + */
> +static int get_key(struct inode *inode, struct cleancache_filekey *key)

Ditto.

> +{
> +	int (*fhfn)(struct dentry *, __u32 *fh, int *, int);
> +	int maxlen = CLEANCACHE_KEY_MAX;
> +	struct super_block *sb = inode->i_sb;
> +	struct dentry *d;
> +	
> +	if (sb->s_export_op && (fhfn = sb->s_export_op->encode_fh)) {
> +		d = list_first_entry(&inode->i_dentry, struct dentry, d_alias);
> +		(void)(*fhfn)(d, &key->u.fh[0], &maxlen, 0); 
> +		if (maxlen > CLEANCACHE_KEY_MAX)
> +			return -1;
> +	}
> +	else
> +		key->u.ino = inode->i_ino;
> +	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 (get_key(page->mapping->host,&key) < 0)
> +		goto out;
> +
> +	ret = (*cleancache_ops.get_page)(pool_id, key, page->index, page);
> +	if (ret == 0)
> +		succ_gets++;
> +	else
> +		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 && get_key(page->mapping->host,&key) >= 0) {
> +		(*cleancache_ops.put_page)(pool_id, key, page->index, page);
> +		puts++;
> +	}
> +}
> +
> +/*
> + * 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)
> +{
> +	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 (get_key(page->mapping->host,&key) >= 0) {
> +			(*cleancache_ops.flush_page)(pool_id, key, page->index);
> +			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 && get_key(mapping->host,&key) >= 0)
> +		(*cleancache_ops.flush_inode)(pool_id, key);
> +}
> +EXPORT_SYMBOL(__cleancache_flush_inode);
> +
> +#ifdef CONFIG_SYSFS
> +
> +/* see Documentation/ABI/xxx/sysfs-kernel-mm-cleancache */
> +
> +#define CLEANCACHE_ATTR_RO(_name) \
> +	static struct kobj_attribute _name##_attr = __ATTR_RO(_name)
> +
> +static ssize_t succ_gets_show(struct kobject *kobj,
> +			       struct kobj_attribute *attr, char *buf)
> +{
> +	return sprintf(buf, "%lu\n", succ_gets);
> +}
> +CLEANCACHE_ATTR_RO(succ_gets);
> +
> +static ssize_t failed_gets_show(struct kobject *kobj,
> +			       struct kobj_attribute *attr, char *buf)
> +{
> +	return sprintf(buf, "%lu\n", failed_gets);
> +}
> +CLEANCACHE_ATTR_RO(failed_gets);
> +
> +static ssize_t puts_show(struct kobject *kobj,
> +			       struct kobj_attribute *attr, char *buf)
> +{
> +	return sprintf(buf, "%lu\n", puts);
> +}
> +CLEANCACHE_ATTR_RO(puts);
> +
> +static ssize_t flushes_show(struct kobject *kobj,
> +			       struct kobj_attribute *attr, char *buf)
> +{
> +	return sprintf(buf, "%lu\n", flushes);
> +}
> +CLEANCACHE_ATTR_RO(flushes);
> +
> +static struct attribute *cleancache_attrs[] = {
> +	&succ_gets_attr.attr,
> +	&failed_gets_attr.attr,
> +	&puts_attr.attr,
> +	&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)
> --- linux-2.6.36-rc3/mm/Kconfig	2010-08-29 09:36:04.000000000 -0600
> +++ linux-2.6.36-rc3-cleancache/mm/Kconfig	2010-08-30 09:20:43.000000000 -0600
> @@ -301,3 +301,25 @@ 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 pseudo-RAM driver to cache clean pages"
> +	default y
> +	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 put
> +	  it into a synchronous concurrency-safe page-oriented pseudo-RAM
> +	  device (such as Xen's Transcendent Memory, aka "tmem") which 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 pseudo-RAM device is available, 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
> --- linux-2.6.36-rc3/mm/Makefile	2010-08-29 09:36:04.000000000 -0600
> +++ linux-2.6.36-rc3-cleancache/mm/Makefile	2010-08-30 09:20:43.000000000 -0600
> @@ -47,3 +47,4 @@ obj-$(CONFIG_MEMORY_FAILURE) += memory-f
>  obj-$(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
>

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