Re: [PATCHv3 3/6] mm/zpool: implement common zpool api to zbud/zsmalloc

[Seth Jennings]

On Sat, May 24, 2014 at 03:06:06PM -0400, Dan Streetman wrote:
> Add zpool api.
> 
> zpool provides an interface for memory storage, typically of compressed
> memory.  Users can select what backend to use; currently the only
> implementations are zbud, a low density implementation with up to
> two compressed pages per storage page, and zsmalloc, a higher density
> implementation with multiple compressed pages per storage page.
> 
> Signed-off-by: Dan Streetman <ddstreet@xxxxxxxx>
> Cc: Seth Jennings <sjennings@xxxxxxxxxxxxxx>
> Cc: Minchan Kim <minchan@xxxxxxxxxx>
> Cc: Nitin Gupta <ngupta@xxxxxxxxxx>
> Cc: Weijie Yang <weijie.yang@xxxxxxxxxxx>
> ---
> 
> Note this patch set is against the mmotm tree at
> git://git.cmpxchg.org/linux-mmotm.git
> This patch may need context changes to the -next or other trees.
> 
> Changes since v2 : https://lkml.org/lkml/2014/5/7/733
>   -Remove hardcoded zbud/zsmalloc implementations
>   -Add driver (un)register functions
> 
> Changes since v1 https://lkml.org/lkml/2014/4/19/101
>  -add some pr_info() during creation and pr_err() on errors
>  -remove zpool code to call zs_shrink(), since zsmalloc shrinking
>   was removed from this patchset
>  -remove fallback; only specified pool type will be tried
>  -pr_fmt() is defined in zpool to prefix zpool: in any pr_XXX() calls
> 
> 
>  include/linux/zpool.h | 214 ++++++++++++++++++++++++++++++++++++++++++++++++++
>  mm/Kconfig            |  41 ++++++----
>  mm/Makefile           |   1 +
>  mm/zpool.c            | 197 ++++++++++++++++++++++++++++++++++++++++++++++
>  4 files changed, 436 insertions(+), 17 deletions(-)
>  create mode 100644 include/linux/zpool.h
>  create mode 100644 mm/zpool.c
> 
> diff --git a/include/linux/zpool.h b/include/linux/zpool.h
> new file mode 100644
> index 0000000..699ac9b
> --- /dev/null
> +++ b/include/linux/zpool.h
> @@ -0,0 +1,214 @@
> +/*
> + * zpool memory storage api
> + *
> + * Copyright (C) 2014 Dan Streetman
> + *
> + * This is a common frontend for the zbud and zsmalloc memory
> + * storage pool implementations.  Typically, this is used to
> + * store compressed memory.
> + */
> +
> +#ifndef _ZPOOL_H_
> +#define _ZPOOL_H_
> +
> +struct zpool;
> +
> +struct zpool_ops {
> +	int (*evict)(struct zpool *pool, unsigned long handle);
> +};
> +
> +/*
> + * Control how a handle is mapped.  It will be ignored if the
> + * implementation does not support it.  Its use is optional.
> + * Note that this does not refer to memory protection, it
> + * refers to how the memory will be copied in/out if copying
> + * is necessary during mapping; read-write is the safest as
> + * it copies the existing memory in on map, and copies the
> + * changed memory back out on unmap.  Write-only does not copy
> + * in the memory and should only be used for initialization.
> + * If in doubt, use ZPOOL_MM_DEFAULT which is read-write.
> + */
> +enum zpool_mapmode {
> +	ZPOOL_MM_RW, /* normal read-write mapping */
> +	ZPOOL_MM_RO, /* read-only (no copy-out at unmap time) */
> +	ZPOOL_MM_WO, /* write-only (no copy-in at map time) */
> +
> +	ZPOOL_MM_DEFAULT = ZPOOL_MM_RW
> +};
> +
> +/**
> + * zpool_create_pool() - Create a new zpool
> + * @type	The type of the zpool to create (e.g. zbud, zsmalloc)
> + * @flags	What GFP flags should be used when the zpool allocates memory.
> + * @ops		The optional ops callback.
> + *
> + * This creates a new zpool of the specified type.  The zpool will use the
> + * given flags when allocating any memory.  If the ops param is NULL, then
> + * the created zpool will not be shrinkable.
> + *
> + * Returns: New zpool on success, NULL on failure.
> + */
> +struct zpool *zpool_create_pool(char *type, gfp_t flags,
> +			struct zpool_ops *ops);
> +
> +/**
> + * zpool_get_type() - Get the type of the zpool
> + * @pool	The zpool to check
> + *
> + * This returns the type of the pool.
> + *
> + * Returns: The type of zpool.
> + */
> +char *zpool_get_type(struct zpool *pool);
> +
> +/**
> + * zpool_destroy_pool() - Destroy a zpool
> + * @pool	The zpool to destroy.
> + *
> + * This destroys an existing zpool.  The zpool should not be in use.
> + */
> +void zpool_destroy_pool(struct zpool *pool);
> +
> +/**
> + * zpool_malloc() - Allocate memory
> + * @pool	The zpool to allocate from.
> + * @size	The amount of memory to allocate.
> + * @handle	Pointer to the handle to set
> + *
> + * This allocates the requested amount of memory from the pool.
> + * The provided @handle will be set to the allocated object handle.
> + *
> + * Returns: 0 on success, negative value on error.
> + */
> +int zpool_malloc(struct zpool *pool, size_t size, unsigned long *handle);
> +
> +/**
> + * zpool_free() - Free previously allocated memory
> + * @pool	The zpool that allocated the memory.
> + * @handle	The handle to the memory to free.
> + *
> + * This frees previously allocated memory.  This does not guarantee
> + * that the pool will actually free memory, only that the memory
> + * in the pool will become available for use by the pool.
> + */
> +void zpool_free(struct zpool *pool, unsigned long handle);
> +
> +/**
> + * zpool_shrink() - Shrink the pool size
> + * @pool	The zpool to shrink.
> + * @size	The minimum amount to shrink the pool.
> + *
> + * This attempts to shrink the actual memory size of the pool
> + * by evicting currently used handle(s).  If the pool was
> + * created with no zpool_ops, or the evict call fails for any
> + * of the handles, this will fail.
> + *
> + * Returns: 0 on success, negative value on error/failure.
> + */
> +int zpool_shrink(struct zpool *pool, size_t size);

This should take a number of pages to be reclaimed, not a size.  The
user can evict their own object to reclaim a certain number of bytes
from the pool.  What the user can't do is reclaim a page since it is not
aware of the arrangement of the stored objects in the memory pages.

Also in patch 5/6 of six I see:

-		if (zbud_reclaim_page(zswap_pool, 8)) {
+		if (zpool_shrink(zswap_pool, PAGE_SIZE)) {

but then in 4/6 I see:

+int zbud_zpool_shrink(void *pool, size_t size)
+{
+	return zbud_reclaim_page(pool, 8);
+}

That is why it didn't completely explode on you since the zbud logic
is still reclaiming pages.

> +
> +/**
> + * zpool_map_handle() - Map a previously allocated handle into memory
> + * @pool	The zpool that the handle was allocated from
> + * @handle	The handle to map
> + * @mm	How the memory should be mapped
> + *
> + * This maps a previously allocated handle into memory.  The @mm
> + * param indicates to the implemenation how the memory will be
> + * used, i.e. read-only, write-only, read-write.  If the
> + * implementation does not support it, the memory will be treated
> + * as read-write.
> + *
> + * This may hold locks, disable interrupts, and/or preemption,
> + * and the zpool_unmap_handle() must be called to undo those
> + * actions.  The code that uses the mapped handle should complete
> + * its operatons on the mapped handle memory quickly and unmap
> + * as soon as possible.  Multiple handles should not be mapped
> + * concurrently on a cpu.
> + *
> + * Returns: A pointer to the handle's mapped memory area.
> + */
> +void *zpool_map_handle(struct zpool *pool, unsigned long handle,
> +			enum zpool_mapmode mm);
> +
> +/**
> + * zpool_unmap_handle() - Unmap a previously mapped handle
> + * @pool	The zpool that the handle was allocated from
> + * @handle	The handle to unmap
> + *
> + * This unmaps a previously mapped handle.  Any locks or other
> + * actions that the implemenation took in zpool_map_handle()
> + * will be undone here.  The memory area returned from
> + * zpool_map_handle() should no longer be used after this.
> + */
> +void zpool_unmap_handle(struct zpool *pool, unsigned long handle);
> +
> +/**
> + * zpool_get_total_size() - The total size of the pool
> + * @pool	The zpool to check
> + *
> + * This returns the total size in bytes of the pool.
> + *
> + * Returns: Total size of the zpool in bytes.
> + */
> +u64 zpool_get_total_size(struct zpool *pool);
> +
> +
> +/**
> + * struct zpool_driver - driver implementation for zpool
> + * @type:	name of the driver.
> + * @list:	entry in the list of zpool drivers.
> + * @create:	create a new pool.
> + * @destroy:	destroy a pool.
> + * @malloc:	allocate mem from a pool.
> + * @free:	free mem from a pool.
> + * @shrink:	shrink the pool.
> + * @map:	map a handle.
> + * @unmap:	unmap a handle.
> + * @total_size:	get total size of a pool.
> + *
> + * This is created by a zpool implementation and registered
> + * with zpool.
> + */
> +struct zpool_driver {
> +	char *type;
> +	struct list_head list;
> +
> +	void *(*create)(gfp_t gfp, struct zpool_ops *ops);
> +	void (*destroy)(void *pool);
> +
> +	int (*malloc)(void *pool, size_t size, unsigned long *handle);
> +	void (*free)(void *pool, unsigned long handle);
> +
> +	int (*shrink)(void *pool, size_t size);
> +
> +	void *(*map)(void *pool, unsigned long handle,
> +				enum zpool_mapmode mm);
> +	void (*unmap)(void *pool, unsigned long handle);
> +
> +	u64 (*total_size)(void *pool);
> +};
> +
> +/**
> + * zpool_register_driver() - register a zpool implementation.
> + * @driver:	driver to register
> + */
> +void zpool_register_driver(struct zpool_driver *driver);
> +
> +/**
> + * zpool_unregister_driver() - unregister a zpool implementation.
> + * @driver:	driver to unregister.
> + */
> +void zpool_unregister_driver(struct zpool_driver *driver);
> +
> +/**
> + * zpool_evict() - evict callback from a zpool implementation.
> + * @pool:	pool to evict from.
> + * @handle:	handle to evict.
> + *
> + * This can be used by zpool implementations to call the
> + * user's evict zpool_ops struct evict callback.
> + */
> +int zpool_evict(void *pool, unsigned long handle);
> +
> +#endif
> diff --git a/mm/Kconfig b/mm/Kconfig
> index 7511b4a..00f7720 100644
> --- a/mm/Kconfig
> +++ b/mm/Kconfig
> @@ -515,15 +515,17 @@ config CMA_DEBUG
>  	  processing calls such as dma_alloc_from_contiguous().
>  	  This option does not affect warning and error messages.
>  
> -config ZBUD
> -	tristate
> -	default n
> +config MEM_SOFT_DIRTY
> +	bool "Track memory changes"
> +	depends on CHECKPOINT_RESTORE && HAVE_ARCH_SOFT_DIRTY && PROC_FS
> +	select PROC_PAGE_MONITOR
>  	help
> -	  A special purpose allocator for storing compressed pages.
> -	  It is designed to store up to two compressed pages per physical
> -	  page.  While this design limits storage density, it has simple and
> -	  deterministic reclaim properties that make it preferable to a higher
> -	  density approach when reclaim will be used.
> +	  This option enables memory changes tracking by introducing a
> +	  soft-dirty bit on pte-s. This bit it set when someone writes
> +	  into a page just as regular dirty bit, but unlike the latter
> +	  it can be cleared by hands.
> +
> +	  See Documentation/vm/soft-dirty.txt for more details.
>  
>  config ZSWAP
>  	bool "Compressed cache for swap pages (EXPERIMENTAL)"
> @@ -545,17 +547,22 @@ config ZSWAP
>  	  they have not be fully explored on the large set of potential
>  	  configurations and workloads that exist.
>  
> -config MEM_SOFT_DIRTY
> -	bool "Track memory changes"
> -	depends on CHECKPOINT_RESTORE && HAVE_ARCH_SOFT_DIRTY && PROC_FS
> -	select PROC_PAGE_MONITOR
> +config ZPOOL
> +	tristate "Common API for compressed memory storage"
> +	default n
>  	help
> -	  This option enables memory changes tracking by introducing a
> -	  soft-dirty bit on pte-s. This bit it set when someone writes
> -	  into a page just as regular dirty bit, but unlike the latter
> -	  it can be cleared by hands.
> +	  Compressed memory storage API.  This allows using either zbud or
> +	  zsmalloc.
>  
> -	  See Documentation/vm/soft-dirty.txt for more details.
> +config ZBUD
> +	tristate "Low density storage for compressed pages"
> +	default n
> +	help
> +	  A special purpose allocator for storing compressed pages.
> +	  It is designed to store up to two compressed pages per physical
> +	  page.  While this design limits storage density, it has simple and
> +	  deterministic reclaim properties that make it preferable to a higher
> +	  density approach when reclaim will be used.
>  
>  config ZSMALLOC
>  	tristate "Memory allocator for compressed pages"
> diff --git a/mm/Makefile b/mm/Makefile
> index 2b6fff2..759db04 100644
> --- a/mm/Makefile
> +++ b/mm/Makefile
> @@ -61,6 +61,7 @@ obj-$(CONFIG_DEBUG_KMEMLEAK_TEST) += kmemleak-test.o
>  obj-$(CONFIG_CLEANCACHE) += cleancache.o
>  obj-$(CONFIG_MEMORY_ISOLATION) += page_isolation.o
>  obj-$(CONFIG_PAGE_OWNER) += pageowner.o
> +obj-$(CONFIG_ZPOOL)	+= zpool.o
>  obj-$(CONFIG_ZBUD)	+= zbud.o
>  obj-$(CONFIG_ZSMALLOC)	+= zsmalloc.o
>  obj-$(CONFIG_GENERIC_EARLY_IOREMAP) += early_ioremap.o
> diff --git a/mm/zpool.c b/mm/zpool.c
> new file mode 100644
> index 0000000..89ed71f
> --- /dev/null
> +++ b/mm/zpool.c
> @@ -0,0 +1,197 @@
> +/*
> + * zpool memory storage api
> + *
> + * Copyright (C) 2014 Dan Streetman
> + *
> + * This is a common frontend for memory storage pool implementations.
> + * Typically, this is used to store compressed memory.
> + */
> +
> +#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
> +
> +#include <linux/list.h>
> +#include <linux/types.h>
> +#include <linux/mm.h>
> +#include <linux/slab.h>
> +#include <linux/spinlock.h>
> +#include <linux/module.h>
> +#include <linux/zpool.h>
> +
> +struct zpool {
> +	char *type;
> +
> +	struct zpool_driver *driver;
> +	void *pool;
> +	struct zpool_ops *ops;
> +
> +	struct list_head list;
> +};
> +
> +static LIST_HEAD(drivers_head);
> +static DEFINE_SPINLOCK(drivers_lock);
> +
> +static LIST_HEAD(pools_head);
> +static DEFINE_SPINLOCK(pools_lock);
> +
> +void zpool_register_driver(struct zpool_driver *driver)
> +{
> +	spin_lock(&drivers_lock);
> +	list_add(&driver->list, &drivers_head);
> +	spin_unlock(&drivers_lock);
> +}
> +EXPORT_SYMBOL(zpool_register_driver);
> +
> +void zpool_unregister_driver(struct zpool_driver *driver)
> +{
> +	spin_lock(&drivers_lock);
> +	list_del(&driver->list);
> +	spin_unlock(&drivers_lock);
> +}
> +EXPORT_SYMBOL(zpool_unregister_driver);
> +
> +int zpool_evict(void *pool, unsigned long handle)
> +{
> +	struct zpool *zpool;
> +
> +	spin_lock(&pools_lock);
> +	list_for_each_entry(zpool, &pools_head, list) {

You can do a container_of() here:

zpool = container_of(pool, struct zpool, pool);

Seth

> +		if (zpool->pool == pool) {
> +			spin_unlock(&pools_lock);
> +			if (!zpool->ops || !zpool->ops->evict)
> +				return -EINVAL;
> +			return zpool->ops->evict(zpool, handle);
> +		}
> +	}
> +	spin_unlock(&pools_lock);
> +
> +	return -ENOENT;
> +}
> +EXPORT_SYMBOL(zpool_evict);
> +
> +static struct zpool_driver *zpool_get_driver(char *type)
> +{
> +	struct zpool_driver *driver;
> +
> +	assert_spin_locked(&drivers_lock);
> +	list_for_each_entry(driver, &drivers_head, list) {
> +		if (!strcmp(driver->type, type))
> +			return driver;
> +	}
> +
> +	return NULL;
> +}
> +
> +struct zpool *zpool_create_pool(char *type, gfp_t flags,
> +			struct zpool_ops *ops)
> +{
> +	struct zpool_driver *driver;
> +	struct zpool *zpool;
> +
> +	pr_info("creating pool type %s\n", type);
> +
> +	spin_lock(&drivers_lock);
> +	driver = zpool_get_driver(type);
> +	spin_unlock(&drivers_lock);
> +
> +	if (!driver) {
> +		request_module(type);
> +		spin_lock(&drivers_lock);
> +		driver = zpool_get_driver(type);
> +		spin_unlock(&drivers_lock);
> +	}
> +
> +	if (!driver) {
> +		pr_err("no driver for type %s\n", type);
> +		return NULL;
> +	}
> +
> +	zpool = kmalloc(sizeof(*zpool), GFP_KERNEL);
> +	if (!zpool) {
> +		pr_err("couldn't create zpool - out of memory\n");
> +		return NULL;
> +	}
> +
> +	zpool->type = driver->type;
> +	zpool->driver = driver;
> +	zpool->pool = driver->create(flags, ops);
> +	zpool->ops = ops;
> +
> +	if (!zpool->pool) {
> +		pr_err("couldn't create %s pool\n", type);
> +		kfree(zpool);
> +		return NULL;
> +	}
> +
> +	pr_info("created %s pool\n", type);
> +
> +	spin_lock(&pools_lock);
> +	list_add(&zpool->list, &pools_head);
> +	spin_unlock(&pools_lock);
> +
> +	return zpool;
> +}
> +
> +void zpool_destroy_pool(struct zpool *zpool)
> +{
> +	pr_info("destroying pool type %s\n", zpool->type);
> +
> +	spin_lock(&pools_lock);
> +	list_del(&zpool->list);
> +	spin_unlock(&pools_lock);
> +	zpool->driver->destroy(zpool->pool);
> +	kfree(zpool);
> +}
> +
> +char *zpool_get_type(struct zpool *zpool)
> +{
> +	return zpool->type;
> +}
> +
> +int zpool_malloc(struct zpool *zpool, size_t size, unsigned long *handle)
> +{
> +	return zpool->driver->malloc(zpool->pool, size, handle);
> +}
> +
> +void zpool_free(struct zpool *zpool, unsigned long handle)
> +{
> +	zpool->driver->free(zpool->pool, handle);
> +}
> +
> +int zpool_shrink(struct zpool *zpool, size_t size)
> +{
> +	return zpool->driver->shrink(zpool->pool, size);
> +}
> +
> +void *zpool_map_handle(struct zpool *zpool, unsigned long handle,
> +			enum zpool_mapmode mapmode)
> +{
> +	return zpool->driver->map(zpool->pool, handle, mapmode);
> +}
> +
> +void zpool_unmap_handle(struct zpool *zpool, unsigned long handle)
> +{
> +	zpool->driver->unmap(zpool->pool, handle);
> +}
> +
> +u64 zpool_get_total_size(struct zpool *zpool)
> +{
> +	return zpool->driver->total_size(zpool->pool);
> +}
> +
> +static int __init init_zpool(void)
> +{
> +	pr_info("loaded\n");
> +	return 0;
> +}
> +
> +static void __exit exit_zpool(void)
> +{
> +	pr_info("unloaded\n");
> +}
> +
> +module_init(init_zpool);
> +module_exit(exit_zpool);
> +
> +MODULE_LICENSE("GPL");
> +MODULE_AUTHOR("Dan Streetman <ddstreet@xxxxxxxx>");
> +MODULE_DESCRIPTION("Common API for compressed memory storage");
> -- 
> 1.8.3.1
> 
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