On Wed, Sep 28, 2022 at 8:38 PM Yosry Ahmed <yosryahmed@xxxxxxxxxx> wrote:
>
> On Wed, Sep 28, 2022 at 1:06 AM ananda <a.badmaev@xxxxxxxxxxxx> wrote:
> >
> > From: Ananda <a.badmaev@xxxxxxxxxxxx>
> >
> > Zblock stores integer number of compressed objects per zblock block.
> > These blocks consist of several physical pages (1/2/4/8) and are arranged
> > in linked lists.
> > The range from 0 to PAGE_SIZE is divided into the number of intervals
> > corresponding to the number of lists and each list only operates objects
> > of size from its interval. Thus the block lists are isolated from each
> > other, which makes it possible to simultaneously perform actions with
> > several objects from different lists.
> > Blocks make it possible to densely arrange objects of various sizes
> > resulting in low internal fragmentation. Also this allocator tries to fill
> > incomplete blocks instead of adding new ones thus in many cases providing
> > a compression ratio substantially higher than z3fold and zbud.
> > Zblock does not require MMU and also is superior to zsmalloc with
> > regard to the worst execution times, thus allowing for better response time
> > and real-time characteristics of the whole system.
> >
>
> It seems to me, and I can be wrong, that there is some overlap in
> design and goals between this zpool backend and zsmalloc. They both
> try to avoid internal fragmentation by avoiding the static slots used
> by zbud and z3fold, and instead pack compressed pages more
> dynamically. They both have some sort of concurrency handling
> (separate block lists in zblock vs. classes in zsmalloc). A key
> difference is that zsmalloc avoids higher order allocations (at least
> based on its docs), and instead allows compressed pages to span across
> 0-order page boundaries.
Well, another key difference is that zsmalloc may only work on
MMU-enabled systems.
> The key differences I see here (based on this commit message and
> zsmalloc docs) are:
> a) Blocks in zblock can consist of higher order pages.
> b) Compressed pages in zsmalloc can span page boundaries (I am
> assuming this isn't the case for zblock).
>
> It appears to me that if zblock has better performance than zsmalloc,
> it can be because pages in zblock are physically contiguous vs. the
> 0-order pages in zsmalloc (TLB misses, cache misses, etc). Is my
> assumption correct?
>
> If yes, would it be better to implement those changes as some tunable
> extension to zsmalloc? It would make it easier if we have overall less
> zpool backends, and also easier for current users of zsmalloc to
> experiment with these changes.
Easier to whom? Not for me, nor for anyone using zswap, that's what I
have to say.
zpool API is created to unify compression backends and so I would
strongly prefer continuing having zpool for backend configuration and
selection, rather than implementing a custom in-zsmalloc selection
mechanism.
I don't think merging is a good idea, and here are the reasons:
- zsmalloc's code is already almost incomprehensible
- zsmalloc's main objective is density, while zblock aims for low latency
- merging the two approaches within zsmalloc would mean creating some
internal selection mechanism within zsmalloc which I would absolutely
like to avoid (for smaller RAM devices I usually don't compile
zsmalloc at all or compile it as a module).
Thanks,
Vitaly
> > Signed-off-by: Ananda <a.badmaev@xxxxxxxxxxxx>
> > ---
> >
> > v2: fixed compiler warnings
> >
> > v3: added documentation and const modifier to struct tree_descr
> >
> > v4: - fixed gfp flags for block allocation
> > - fixed potential memory leak when allocating blocks
> > - resolved some issues with code style and warnings from checkpatch
> > (except warning about single line config symbol description)
> > - moved test results from documentation to changelog
> >
> > v5: - "direct" handle mapping and use of linked lists instead of red-black
> > trees resulting in faster operations and a bit simpler code
> > - renamed ztree -> zblock
> > - edited various comments and descriptions
> >
> > Documentation/mm/zblock.rst | 31 ++
> > MAINTAINERS | 7 +
> > mm/Kconfig | 17 +
> > mm/Makefile | 1 +
> > mm/zblock.c | 637 ++++++++++++++++++++++++++++++++++++
> > 5 files changed, 693 insertions(+)
> > create mode 100644 Documentation/mm/zblock.rst
> > create mode 100644 mm/zblock.c
> >
> > diff --git a/Documentation/mm/zblock.rst b/Documentation/mm/zblock.rst
> > new file mode 100644
> > index 000000000000..5008ce90b54b
> > --- /dev/null
> > +++ b/Documentation/mm/zblock.rst
> > @@ -0,0 +1,31 @@
> > +.. SPDX-License-Identifier: GPL-2.0
> > +
> > +.. _block:
> > +
> > +======
> > +zblock
> > +======
> > +
> > +Zblock stores integer number of compressed objects per block. These
> > +blocks consist of several consecutive physical pages (from 1 to 8) and
> > +are arranged in lists. The range from 0 to PAGE_SIZE is divided into the
> > +number of intervals corresponding to the number of lists and each list
> > +only operates objects of size from its interval. Thus the block lists are
> > +isolated from each other, which makes it possible to simultaneously
> > +perform actions with several objects from different lists.
> > +
> > +Blocks make it possible to densely arrange objects of various sizes
> > +resulting in low internal fragmentation. Also this allocator tries to fill
> > +incomplete blocks instead of adding new ones thus in many cases providing
> > +a compression ratio substantially higher than z3fold and zbud. Zblock does
> > +not require MMU and also is superior to zsmalloc with regard to the worst
> > +execution times, thus allowing for better response time and real-time
> > +characteristics of the whole system.
> > +
> > +Like z3fold and zsmalloc zblock_alloc() does not return a dereferenceable
> > +pointer. Instead, it returns an unsigned long handle which encodes actual
> > +location of the allocated object.
> > +
> > +Unlike zbud and z3fold zblock works well with objects of various sizes - both
> > +highly compressed and poorly compressed including cases where both types
> > +are present.
> > diff --git a/MAINTAINERS b/MAINTAINERS
> > index f1390b8270b2..014fb19eb2cc 100644
> > --- a/MAINTAINERS
> > +++ b/MAINTAINERS
> > @@ -22457,6 +22457,13 @@ L: linux-mm@xxxxxxxxx
> > S: Maintained
> > F: mm/z3fold.c
> >
> > +ZBLOCK COMPRESSED PAGE ALLOCATOR
> > +M: Ananda Badmaev <a.badmaev@xxxxxxxxxxxx>
> > +M: Vitaly Wool <vitaly.wool@xxxxxxxxxxxx>
> > +L: linux-mm@xxxxxxxxx
> > +S: Maintained
> > +F: mm/zblock.c
> > +
> > ZD1211RW WIRELESS DRIVER
> > M: Ulrich Kunitz <kune@xxxxxxxxxxxxxx>
> > L: linux-wireless@xxxxxxxxxxxxxxx
> > diff --git a/mm/Kconfig b/mm/Kconfig
> > index 0331f1461f81..470c80f5726d 100644
> > --- a/mm/Kconfig
> > +++ b/mm/Kconfig
> > @@ -149,6 +149,12 @@ config ZSWAP_ZPOOL_DEFAULT_ZSMALLOC
> > select ZSMALLOC
> > help
> > Use the zsmalloc allocator as the default allocator.
> > +
> > +config ZSWAP_ZPOOL_DEFAULT_ZBLOCK
> > + bool "zblock"
> > + select ZBLOCK
> > + help
> > + Use the zblock allocator as the default allocator.
> > endchoice
> >
> > config ZSWAP_ZPOOL_DEFAULT
> > @@ -157,6 +163,7 @@ config ZSWAP_ZPOOL_DEFAULT
> > default "zbud" if ZSWAP_ZPOOL_DEFAULT_ZBUD
> > default "z3fold" if ZSWAP_ZPOOL_DEFAULT_Z3FOLD
> > default "zsmalloc" if ZSWAP_ZPOOL_DEFAULT_ZSMALLOC
> > + default "zblock" if ZSWAP_ZPOOL_DEFAULT_ZBLOCK
> > default ""
> >
> > config ZBUD
> > @@ -187,6 +194,16 @@ config ZSMALLOC
> > pages of various compression levels efficiently. It achieves
> > the highest storage density with the least amount of fragmentation.
> >
> > +config ZBLOCK
> > + tristate "Simple block allocator (zblock)"
> > + depends on ZPOOL
> > + help
> > + A special purpose allocator for storing compressed pages.
> > + It stores integer number of compressed pages per block and
> > + each block consists of number of physical pages being a power of 2.
> > + zblock provides fast read/write, limited worst case time for
> > + operations and good compression ratio in most scenarios.
> > +
> > config ZSMALLOC_STAT
> > bool "Export zsmalloc statistics"
> > depends on ZSMALLOC
> > diff --git a/mm/Makefile b/mm/Makefile
> > index 9a564f836403..eb7235da6e61 100644
> > --- a/mm/Makefile
> > +++ b/mm/Makefile
> > @@ -110,6 +110,7 @@ obj-$(CONFIG_ZPOOL) += zpool.o
> > obj-$(CONFIG_ZBUD) += zbud.o
> > obj-$(CONFIG_ZSMALLOC) += zsmalloc.o
> > obj-$(CONFIG_Z3FOLD) += z3fold.o
> > +obj-$(CONFIG_ZBLOCK) += zblock.o
> > obj-$(CONFIG_GENERIC_EARLY_IOREMAP) += early_ioremap.o
> > obj-$(CONFIG_CMA) += cma.o
> > obj-$(CONFIG_MEMORY_BALLOON) += balloon_compaction.o
> > diff --git a/mm/zblock.c b/mm/zblock.c
> > new file mode 100644
> > index 000000000000..b389f43e0c26
> > --- /dev/null
> > +++ b/mm/zblock.c
> > @@ -0,0 +1,637 @@
> > +// SPDX-License-Identifier: GPL-2.0-only
> > +/*
> > + * zblock.c
> > + *
> > + * Author: Ananda Badmaev <a.badmaev@xxxxxxxxxxxx>
> > + * Copyright (C) 2022, Konsulko AB.
> > + *
> > + * This implementation is based on z3fold written by Vitaly Wool.
> > + * Zblock is a small object allocator with the intention to serve as a
> > + * zpool backend. It operates on page blocks which consist of number
> > + * of physical pages being a power of 2 and store integer number of
> > + * compressed pages per block which results in determinism and simplicity.
> > + *
> > + * zblock doesn't export any API and is meant to be used via zpool API.
> > + */
> > +
> > +#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
> > +
> > +#include <linux/atomic.h>
> > +#include <linux/list.h>
> > +#include <linux/mm.h>
> > +#include <linux/module.h>
> > +#include <linux/preempt.h>
> > +#include <linux/slab.h>
> > +#include <linux/spinlock.h>
> > +#include <linux/zpool.h>
> > +
> > +#define SLOT_FREE 0
> > +#define SLOT_OCCUPIED 1
> > +#define SLOT_MAPPED 2
> > +#define SLOT_UNMAPPED 3
> > +
> > +#define SLOT_BITS 5
> > +#define MAX_SLOTS (1 << SLOT_BITS)
> > +#define SLOT_MASK ((0x1UL << SLOT_BITS) - 1)
> > +
> > +#define BLOCK_DATA_SIZE(order) ((PAGE_SIZE << order) - sizeof(struct zblock_block))
> > +#define SLOT_SIZE(nslots, order) (round_down((BLOCK_DATA_SIZE(order) / nslots), sizeof(long)))
> > +
> > +#define BLOCK_CACHE_SIZE 32
> > +
> > +struct zblock_pool;
> > +
> > +struct zblock_ops {
> > + int (*evict)(struct zblock_pool *pool, unsigned long handle);
> > +};
> > +
> > +/**
> > + * struct zblock_block - block metadata
> > + * Block consists of several (1/2/4/8) pages and contains fixed
> > + * integer number of slots for allocating compressed pages.
> > + *
> > + * lock: protects block
> > + * block_node: links block into the relevant list in the pool
> > + * slot_info: contains data about free/occupied slots
> > + * free_slots: number of free slots in the block
> > + * under_reclaim: if true shows that block is being evicted
> > + */
> > +struct zblock_block {
> > + spinlock_t lock;
> > + struct list_head block_node;
> > + u8 slot_info[MAX_SLOTS];
> > + unsigned int free_slots;
> > + bool under_reclaim;
> > +};
> > +/**
> > + * struct block_desc - general metadata for block lists
> > + * Each block list stores only blocks of corresponding type which means
> > + * that all blocks in it have the same number and size of slots.
> > + * All slots are aligned to size of long.
> > + *
> > + * slot_size: size of slot for this list
> > + * slots_per_block: number of slots per block for this list
> > + * order: order for __get_free_pages
> > + */
> > +static const struct block_desc {
> > + const unsigned int slot_size;
> > + const unsigned short slots_per_block;
> > + const unsigned short order;
> > +} block_desc[] = {
> > + { SLOT_SIZE(32, 0), 32, 0 },
> > + { SLOT_SIZE(22, 0), 22, 0 },
> > + { SLOT_SIZE(17, 0), 17, 0 },
> > + { SLOT_SIZE(13, 0), 13, 0 },
> > + { SLOT_SIZE(11, 0), 11, 0 },
> > + { SLOT_SIZE(9, 0), 9, 0 },
> > + { SLOT_SIZE(8, 0), 8, 0 },
> > + { SLOT_SIZE(14, 1), 14, 1 },
> > + { SLOT_SIZE(12, 1), 12, 1 },
> > + { SLOT_SIZE(11, 1), 11, 1 },
> > + { SLOT_SIZE(10, 1), 10, 1 },
> > + { SLOT_SIZE(9, 1), 9, 1 },
> > + { SLOT_SIZE(8, 1), 8, 1 },
> > + { SLOT_SIZE(15, 2), 15, 2 },
> > + { SLOT_SIZE(14, 2), 14, 2 },
> > + { SLOT_SIZE(13, 2), 13, 2 },
> > + { SLOT_SIZE(12, 2), 12, 2 },
> > + { SLOT_SIZE(11, 2), 11, 2 },
> > + { SLOT_SIZE(10, 2), 10, 2 },
> > + { SLOT_SIZE(9, 2), 9, 2 },
> > + { SLOT_SIZE(8, 2), 8, 2 },
> > + { SLOT_SIZE(15, 3), 15, 3 },
> > + { SLOT_SIZE(14, 3), 14, 3 },
> > + { SLOT_SIZE(13, 3), 13, 3 },
> > + { SLOT_SIZE(12, 3), 12, 3 },
> > + { SLOT_SIZE(11, 3), 11, 3 },
> > + { SLOT_SIZE(10, 3), 10, 3 },
> > + { SLOT_SIZE(9, 3), 9, 3 },
> > + { SLOT_SIZE(7, 3), 7, 3 }
> > +};
> > +
> > +/**
> > + * struct block_list - stores metadata of particular list
> > + * lock: protects list
> > + * head: head of this list
> > + * block_cache: blocks with free slots
> > + * block_count: total number of blocks in the list
> > + */
> > +struct block_list {
> > + spinlock_t lock;
> > + struct list_head head;
> > + struct zblock_block *block_cache[BLOCK_CACHE_SIZE];
> > + unsigned long block_count;
> > +};
> > +
> > +/**
> > + * struct zblock_pool - stores metadata for each zblock pool
> > + * @block_lists: array of block lists
> > + * @ops: pointer to a structure of user defined operations specified at
> > + * pool creation time.
> > + * @zpool: zpool driver
> > + * @zpool_ops: zpool operations structure with an evict callback
> > + * @alloc_flag: protects block allocation from memory leak
> > + *
> > + * This structure is allocated at pool creation time and maintains metadata
> > + * for a particular zblock pool.
> > + */
> > +struct zblock_pool {
> > + struct block_list block_lists[ARRAY_SIZE(block_desc)];
> > + const struct zblock_ops *ops;
> > + struct zpool *zpool;
> > + const struct zpool_ops *zpool_ops;
> > + atomic_t alloc_flag;
> > +};
> > +
> > +/*****************
> > + * Helpers
> > + *****************/
> > +
> > +static void cache_insert_block(struct zblock_block *block, struct block_list *list)
> > +{
> > + unsigned int i, min_free_slots, min_index;
> > +
> > + min_free_slots = MAX_SLOTS;
> > + for (i = 0; i < BLOCK_CACHE_SIZE; i++) {
> > + if (!list->block_cache[i] || !(list->block_cache[i])->free_slots) {
> > + list->block_cache[i] = block;
> > + return;
> > + }
> > + if ((list->block_cache[i])->free_slots < min_free_slots) {
> > + min_free_slots = (list->block_cache[i])->free_slots;
> > + min_index = i;
> > + }
> > + }
> > + list->block_cache[min_index] = block;
> > +}
> > +
> > +static struct zblock_block *cache_find_block(struct block_list *list)
> > +{
> > + int i;
> > +
> > + for (i = 0; i < BLOCK_CACHE_SIZE; i++) {
> > + if (list->block_cache[i] && (list->block_cache[i])->free_slots)
> > + return list->block_cache[i];
> > + }
> > + return NULL;
> > +}
> > +
> > +static int is_in_cache(struct zblock_block *block, struct block_list *list)
> > +{
> > + int i;
> > +
> > + for (i = 0; i < BLOCK_CACHE_SIZE; i++) {
> > + if (block == list->block_cache[i])
> > + return i;
> > + }
> > + return -1;
> > +}
> > +
> > +/*
> > + * allocate new block and add it to corresponding block list
> > + */
> > +static struct zblock_block *alloc_block(struct zblock_pool *pool,
> > + int block_type, gfp_t gfp)
> > +{
> > + struct zblock_block *block;
> > + struct block_list *list;
> > +
> > + block = (void *)__get_free_pages(gfp, block_desc[block_type].order);
> > + if (!block)
> > + return NULL;
> > +
> > + list = &(pool->block_lists)[block_type];
> > +
> > + /* init block data */
> > + spin_lock_init(&block->lock);
> > + memset(block->slot_info, SLOT_FREE, block_desc[block_type].slots_per_block);
> > + block->free_slots = block_desc[block_type].slots_per_block;
> > + block->under_reclaim = false;
> > +
> > + spin_lock(&list->lock);
> > + /* inserting block into list */
> > + INIT_LIST_HEAD(&block->block_node);
> > + list_add(&block->block_node, &list->head);
> > + cache_insert_block(block, list);
> > + list->block_count++;
> > + spin_unlock(&list->lock);
> > + return block;
> > +}
> > +
> > +/*
> > + * Encodes the handle of a particular slot in the pool using metadata
> > + */
> > +static inline unsigned long metadata_to_handle(struct zblock_block *block,
> > + unsigned int block_type, unsigned int slot)
> > +{
> > + return (unsigned long)(block) + (block_type << SLOT_BITS) + slot;
> > +}
> > +
> > +/* Returns block, block type and slot in the pool corresponding to handle */
> > +static inline struct zblock_block *handle_to_metadata(unsigned long handle,
> > + unsigned int *block_type, unsigned int *slot)
> > +{
> > + *block_type = (handle & (PAGE_SIZE - 1)) >> SLOT_BITS;
> > + *slot = handle & SLOT_MASK;
> > + return (struct zblock_block *)(handle & PAGE_MASK);
> > +}
> > +
> > +
> > +/*****************
> > + * API Functions
> > + *****************/
> > +/**
> > + * zblock_create_pool() - create a new zblock pool
> > + * @gfp: gfp flags when allocating the zblock pool structure
> > + * @ops: user-defined operations for the zblock pool
> > + *
> > + * Return: pointer to the new zblock pool or NULL if the metadata allocation
> > + * failed.
> > + */
> > +static struct zblock_pool *zblock_create_pool(gfp_t gfp, const struct zblock_ops *ops)
> > +{
> > + struct zblock_pool *pool;
> > + struct block_list *list;
> > + int i, j;
> > +
> > + pool = kmalloc(sizeof(struct zblock_pool), gfp);
> > + if (!pool)
> > + return NULL;
> > +
> > + /* init each block list */
> > + for (i = 0; i < ARRAY_SIZE(block_desc); i++) {
> > + list = &(pool->block_lists)[i];
> > + spin_lock_init(&list->lock);
> > + INIT_LIST_HEAD(&list->head);
> > + for (j = 0; j < BLOCK_CACHE_SIZE; j++)
> > + list->block_cache[j] = NULL;
> > + list->block_count = 0;
> > + }
> > + pool->ops = ops;
> > + atomic_set(&pool->alloc_flag, 0);
> > + return pool;
> > +}
> > +
> > +/**
> > + * zblock_destroy_pool() - destroys an existing zblock pool
> > + * @pool: the zblock pool to be destroyed
> > + *
> > + */
> > +static void zblock_destroy_pool(struct zblock_pool *pool)
> > +{
> > + kfree(pool);
> > +}
> > +
> > +
> > +/**
> > + * zblock_alloc() - allocates a slot of appropriate size
> > + * @pool: zblock pool from which to allocate
> > + * @size: size in bytes of the desired allocation
> > + * @gfp: gfp flags used if the pool needs to grow
> > + * @handle: handle of the new allocation
> > + *
> > + * Return: 0 if success and handle is set, otherwise -EINVAL if the size or
> > + * gfp arguments are invalid or -ENOMEM if the pool was unable to allocate
> > + * a new slot.
> > + */
> > +static int zblock_alloc(struct zblock_pool *pool, size_t size, gfp_t gfp,
> > + unsigned long *handle)
> > +{
> > + unsigned int block_type, slot;
> > + struct zblock_block *block;
> > + struct block_list *list;
> > +
> > + if (!size)
> > + return -EINVAL;
> > +
> > + if (size > PAGE_SIZE)
> > + return -ENOSPC;
> > +
> > + /* find basic block type with suitable slot size */
> > + for (block_type = 0; block_type < ARRAY_SIZE(block_desc); block_type++) {
> > + if (size <= block_desc[block_type].slot_size)
> > + break;
> > + }
> > + list = &(pool->block_lists[block_type]);
> > +
> > +check:
> > + spin_lock(&list->lock);
> > + /* check if there are free slots in cache */
> > + block = cache_find_block(list);
> > + if (block)
> > + goto found;
> > + spin_unlock(&list->lock);
> > +
> > + /* not found block with free slots try to allocate new empty block */
> > + if (atomic_cmpxchg(&pool->alloc_flag, 0, 1))
> > + goto check;
> > + block = alloc_block(pool, block_type, gfp & ~(__GFP_HIGHMEM | __GFP_MOVABLE));
> > + if (block) {
> > + spin_lock(&list->lock);
> > + goto found;
> > + }
> > + atomic_set(&pool->alloc_flag, 0);
> > + return -ENOMEM;
> > +
> > +found:
> > + spin_lock(&block->lock);
> > + block->free_slots--;
> > + spin_unlock(&list->lock);
> > + /* find the first free slot in block */
> > + for (slot = 0; slot < block_desc[block_type].slots_per_block; slot++) {
> > + if (block->slot_info[slot] == SLOT_FREE)
> > + break;
> > + }
> > + block->slot_info[slot] = SLOT_OCCUPIED;
> > + spin_unlock(&block->lock);
> > + *handle = metadata_to_handle(block, block_type, slot);
> > + atomic_set(&pool->alloc_flag, 0);
> > + return 0;
> > +}
> > +
> > +/**
> > + * zblock_free() - frees the allocation associated with the given handle
> > + * @pool: pool in which the allocation resided
> > + * @handle: handle associated with the allocation returned by zblock_alloc()
> > + *
> > + */
> > +static void zblock_free(struct zblock_pool *pool, unsigned long handle)
> > +{
> > + unsigned int slot, block_type;
> > + struct zblock_block *block;
> > + struct block_list *list;
> > + int i;
> > +
> > + block = handle_to_metadata(handle, &block_type, &slot);
> > + list = &(pool->block_lists[block_type]);
> > +
> > + if (block->under_reclaim)
> > + return;
> > + spin_lock(&list->lock);
> > + i = is_in_cache(block, list);
> > + block->free_slots++;
> > + /* if all slots in block are empty delete whole block */
> > + if (block->free_slots == block_desc[block_type].slots_per_block) {
> > + list_del(&block->block_node);
> > + list->block_count--;
> > +
> > + /* if cached block to be deleted */
> > + if (i != -1)
> > + list->block_cache[i] = NULL;
> > + spin_unlock(&list->lock);
> > + free_pages((unsigned long)block, block_desc[block_type].order);
> > + return;
> > + }
> > + /* if block is not cached update cache */
> > + if (i == -1)
> > + cache_insert_block(block, list);
> > +
> > + spin_lock(&block->lock);
> > + spin_unlock(&list->lock);
> > + block->slot_info[slot] = SLOT_FREE;
> > + spin_unlock(&block->lock);
> > +}
> > +
> > +/**
> > + * zblock_reclaim_block() - evicts allocations from block and frees it
> > + * @pool: pool from which a block will attempt to be evicted
> > + *
> > + * Returns: pages reclaimed count if block is successfully freed
> > + * otherwise -EINVAL if there are no blocks to evict
> > + */
> > +static int zblock_reclaim_block(struct zblock_pool *pool)
> > +{
> > + struct zblock_block *block;
> > + struct block_list *list;
> > + unsigned long handle, block_type, slot;
> > + int ret, i, reclaimed;
> > +
> > + /* start with list storing blocks with the worst compression and try
> > + * to evict the first added (oldest) block in this list
> > + */
> > + for (block_type = ARRAY_SIZE(block_desc) - 1; block_type >= 0; --block_type) {
> > + list = &(pool->block_lists[block_type]);
> > + spin_lock(&list->lock);
> > +
> > + /* find the oldest block in list */
> > + block = list_last_entry(&list->head, struct zblock_block, block_node);
> > +
> > + if (!block) {
> > + spin_unlock(&list->lock);
> > + continue;
> > + }
> > + i = is_in_cache(block, list);
> > + /* skip iteration if this block is cached */
> > + if (i != -1) {
> > + spin_unlock(&list->lock);
> > + continue;
> > + }
> > + block->under_reclaim = true;
> > + spin_unlock(&list->lock);
> > + reclaimed = 0;
> > +
> > + /* try to evict all UNMAPPED slots in block */
> > + for (slot = 0; slot < block_desc[block_type].slots_per_block; ++slot) {
> > + if (block->slot_info[slot] == SLOT_UNMAPPED) {
> > + handle = metadata_to_handle(block, block_type, slot);
> > + ret = pool->ops->evict(pool, handle);
> > + if (ret)
> > + break;
> > +
> > + ++reclaimed;
> > + spin_lock(&block->lock);
> > + block->slot_info[slot] = SLOT_FREE;
> > + spin_unlock(&block->lock);
> > + block->free_slots++;
> > + }
> > + }
> > + spin_lock(&list->lock);
> > + /* some occupied slots remained - insert block */
> > + if (block->free_slots != block_desc[block_type].slots_per_block) {
> > + block->under_reclaim = false;
> > + cache_insert_block(block, list);
> > + spin_unlock(&list->lock);
> > + } else {
> > + /* all slots are free - delete this block */
> > + list_del(&block->block_node);
> > + list->block_count--;
> > + spin_unlock(&list->lock);
> > + free_pages((unsigned long)block, block_desc[block_type].order);
> > + }
> > + if (reclaimed != 0)
> > + return reclaimed;
> > + return -EAGAIN;
> > + }
> > + return -EINVAL;
> > +}
> > +
> > +
> > +/**
> > + * zblock_map() - maps the allocation associated with the given handle
> > + * @pool: pool in which the allocation resides
> > + * @handle: handle associated with the allocation to be mapped
> > + *
> > + *
> > + * Returns: a pointer to the mapped allocation
> > + */
> > +static void *zblock_map(struct zblock_pool *pool, unsigned long handle)
> > +{
> > + unsigned int block_type, slot;
> > + struct zblock_block *block;
> > +
> > + block = handle_to_metadata(handle, &block_type, &slot);
> > + spin_lock(&block->lock);
> > + block->slot_info[slot] = SLOT_MAPPED;
> > + spin_unlock(&block->lock);
> > + return (void *)(block + 1) + slot * block_desc[block_type].slot_size;
> > +}
> > +
> > +/**
> > + * zblock_unmap() - unmaps the allocation associated with the given handle
> > + * @pool: pool in which the allocation resides
> > + * @handle: handle associated with the allocation to be unmapped
> > + */
> > +static void zblock_unmap(struct zblock_pool *pool, unsigned long handle)
> > +{
> > + unsigned int block_type, slot;
> > + struct zblock_block *block;
> > +
> > + block = handle_to_metadata(handle, &block_type, &slot);
> > + spin_lock(&block->lock);
> > + block->slot_info[slot] = SLOT_UNMAPPED;
> > + spin_unlock(&block->lock);
> > +}
> > +
> > +/**
> > + * zblock_get_pool_size() - gets the zblock pool size in bytes
> > + * @pool: pool whose size is being queried
> > + *
> > + * Returns: size in bytes of the given pool.
> > + */
> > +static u64 zblock_get_pool_size(struct zblock_pool *pool)
> > +{
> > + u64 total_size;
> > + int i;
> > +
> > + total_size = 0;
> > + for (i = 0; i < ARRAY_SIZE(block_desc); i++) {
> > + total_size += (pool->block_lists)[i].block_count
> > + * (PAGE_SIZE << block_desc[i].order);
> > + }
> > + return total_size;
> > +}
> > +
> > +/*****************
> > + * zpool
> > + ****************/
> > +
> > +static int zblock_zpool_evict(struct zblock_pool *pool, unsigned long handle)
> > +{
> > + if (pool->zpool && pool->zpool_ops && pool->zpool_ops->evict)
> > + return pool->zpool_ops->evict(pool->zpool, handle);
> > + else
> > + return -ENOENT;
> > +}
> > +
> > +static const struct zblock_ops zblock_zpool_ops = {
> > + .evict = zblock_zpool_evict
> > +};
> > +
> > +static void *zblock_zpool_create(const char *name, gfp_t gfp,
> > + const struct zpool_ops *zpool_ops,
> > + struct zpool *zpool)
> > +{
> > + struct zblock_pool *pool;
> > +
> > + pool = zblock_create_pool(gfp, &zblock_zpool_ops);
> > + if (pool) {
> > + pool->zpool = zpool;
> > + pool->zpool_ops = zpool_ops;
> > + }
> > + return pool;
> > +}
> > +
> > +static void zblock_zpool_destroy(void *pool)
> > +{
> > + zblock_destroy_pool(pool);
> > +}
> > +
> > +static int zblock_zpool_malloc(void *pool, size_t size, gfp_t gfp,
> > + unsigned long *handle)
> > +{
> > + return zblock_alloc(pool, size, gfp, handle);
> > +}
> > +
> > +static void zblock_zpool_free(void *pool, unsigned long handle)
> > +{
> > + zblock_free(pool, handle);
> > +}
> > +
> > +static int zblock_zpool_shrink(void *pool, unsigned int pages,
> > + unsigned int *reclaimed)
> > +{
> > + unsigned int total = 0;
> > + int ret = -EINVAL;
> > +
> > + while (total < pages) {
> > + ret = zblock_reclaim_block(pool);
> > + if (ret < 0)
> > + break;
> > + total += ret;
> > + }
> > + if (reclaimed)
> > + *reclaimed = total;
> > +
> > + return ret;
> > +}
> > +
> > +static void *zblock_zpool_map(void *pool, unsigned long handle,
> > + enum zpool_mapmode mm)
> > +{
> > + return zblock_map(pool, handle);
> > +}
> > +
> > +static void zblock_zpool_unmap(void *pool, unsigned long handle)
> > +{
> > + zblock_unmap(pool, handle);
> > +}
> > +
> > +static u64 zblock_zpool_total_size(void *pool)
> > +{
> > + return zblock_get_pool_size(pool);
> > +}
> > +
> > +static struct zpool_driver zblock_zpool_driver = {
> > + .type = "zblock",
> > + .owner = THIS_MODULE,
> > + .create = zblock_zpool_create,
> > + .destroy = zblock_zpool_destroy,
> > + .malloc = zblock_zpool_malloc,
> > + .free = zblock_zpool_free,
> > + .shrink = zblock_zpool_shrink,
> > + .map = zblock_zpool_map,
> > + .unmap = zblock_zpool_unmap,
> > + .total_size = zblock_zpool_total_size,
> > +};
> > +
> > +MODULE_ALIAS("zpool-zblock");
> > +
> > +static int __init init_zblock(void)
> > +{
> > + pr_info("loaded\n");
> > + zpool_register_driver(&zblock_zpool_driver);
> > + return 0;
> > +}
> > +
> > +static void __exit exit_zblock(void)
> > +{
> > + zpool_unregister_driver(&zblock_zpool_driver);
> > + pr_info("unloaded\n");
> > +}
> > +
> > +module_init(init_zblock);
> > +module_exit(exit_zblock);
> > +
> > +MODULE_LICENSE("GPL");
> > +MODULE_AUTHOR("Ananda Badmaeb <a.badmaev@xxxxxxxxxxxx>");
> > +MODULE_DESCRIPTION("Block allocator for compressed pages");
> > --
> > 2.34.1
> >
> >
