Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758206Ab3ENQCK (ORCPT ); Tue, 14 May 2013 12:02:10 -0400 Received: from e9.ny.us.ibm.com ([32.97.182.139]:57691 "EHLO e9.ny.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1758058Ab3ENQCI (ORCPT ); Tue, 14 May 2013 12:02:08 -0400 Date: Tue, 14 May 2013 11:00:40 -0500 From: Seth Jennings To: Bob Liu Cc: Andrew Morton , Greg Kroah-Hartman , Nitin Gupta , Minchan Kim , Konrad Rzeszutek Wilk , Dan Magenheimer , Robert Jennings , Jenifer Hopper , Mel Gorman , Johannes Weiner , Rik van Riel , Larry Woodman , Benjamin Herrenschmidt , Dave Hansen , Joe Perches , Joonsoo Kim , Cody P Schafer , Hugh Dickens , Paul Mackerras , linux-mm@kvack.org, linux-kernel@vger.kernel.org, devel@driverdev.osuosl.org Subject: Re: [PATCHv11 3/4] zswap: add to mm/ Message-ID: <20130514160040.GB4024@medulla> References: <1368448803-2089-1-git-send-email-sjenning@linux.vnet.ibm.com> <1368448803-2089-4-git-send-email-sjenning@linux.vnet.ibm.com> <51920197.9070105@oracle.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <51920197.9070105@oracle.com> User-Agent: Mutt/1.5.21 (2010-09-15) X-TM-AS-MML: No X-Content-Scanned: Fidelis XPS MAILER x-cbid: 13051416-7182-0000-0000-000006AEEE2D Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 24863 Lines: 754 On Tue, May 14, 2013 at 05:19:19PM +0800, Bob Liu wrote: > Hi Seth, Hi Bob, thanks for the review! > > On 05/13/2013 08:40 PM, Seth Jennings wrote: > > zswap is a thin compression backend for frontswap. It receives pages from > > frontswap and attempts to store them in a compressed memory pool, resulting in > > an effective partial memory reclaim and dramatically reduced swap device I/O. > > > > Additionally, in most cases, pages can be retrieved from this compressed store > > much more quickly than reading from tradition swap devices resulting in faster > > performance for many workloads. > > > > It also has support for evicting swap pages that are currently compressed in > > zswap to the swap device on an LRU(ish) basis. This functionality is very > > important and make zswap a true cache in that, once the cache is full or can't > > grow due to memory pressure, the oldest pages can be moved out of zswap to the > > swap device so newer pages can be compressed and stored in zswap. > > > > This patch adds the zswap driver to mm/ > > > > Signed-off-by: Seth Jennings > > It seems that you didn't address some comments from Mel in > [PATCHv9 4/8] zswap: add to mm/ > > > --- > > mm/Kconfig | 15 + > > mm/Makefile | 1 + > > mm/zswap.c | 952 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ > > 3 files changed, 968 insertions(+) > > create mode 100644 mm/zswap.c > > > > diff --git a/mm/Kconfig b/mm/Kconfig > > index 908f41b..4042e07 100644 > > --- a/mm/Kconfig > > +++ b/mm/Kconfig > > @@ -487,3 +487,18 @@ config ZBUD > > 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 ZSWAP > > + bool "In-kernel swap page compression" > > + depends on FRONTSWAP && CRYPTO > > + select CRYPTO_LZO > > + select ZBUD > > + default n > > + help > > + Zswap is a backend for the frontswap mechanism in the VMM. > > + It receives pages from frontswap and attempts to store them > > + in a compressed memory pool, resulting in an effective > > + partial memory reclaim. In addition, pages and be retrieved > > + from this compressed store much faster than most tradition > > + swap devices resulting in reduced I/O and faster performance > > + for many workloads. > > diff --git a/mm/Makefile b/mm/Makefile > > index 95f0197..f008033 100644 > > --- a/mm/Makefile > > +++ b/mm/Makefile > > @@ -32,6 +32,7 @@ obj-$(CONFIG_HAVE_MEMBLOCK) += memblock.o > > obj-$(CONFIG_BOUNCE) += bounce.o > > obj-$(CONFIG_SWAP) += page_io.o swap_state.o swapfile.o > > obj-$(CONFIG_FRONTSWAP) += frontswap.o > > +obj-$(CONFIG_ZSWAP) += zswap.o > > obj-$(CONFIG_HAS_DMA) += dmapool.o > > obj-$(CONFIG_HUGETLBFS) += hugetlb.o > > obj-$(CONFIG_NUMA) += mempolicy.o > > diff --git a/mm/zswap.c b/mm/zswap.c > > new file mode 100644 > > index 0000000..b1070ca > > --- /dev/null > > +++ b/mm/zswap.c > > @@ -0,0 +1,952 @@ > > +/* > > + * zswap.c - zswap driver file > > + * > > + * zswap is a backend for frontswap that takes pages that are in the > > + * process of being swapped out and attempts to compress them and store > > + * them in a RAM-based memory pool. This results in a significant I/O > > + * reduction on the real swap device and, in the case of a slow swap > > + * device, can also improve workload performance. > > + * > > + * Copyright (C) 2012 Seth Jennings > > + * > > + * This program is free software; you can redistribute it and/or > > + * modify it under the terms of the GNU General Public License > > + * as published by the Free Software Foundation; either version 2 > > + * of the License, or (at your option) any later version. > > + * > > + * This program is distributed in the hope that it will be useful, > > + * but WITHOUT ANY WARRANTY; without even the implied warranty of > > + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the > > + * GNU General Public License for more details. > > +*/ > > + > > +#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt > > + > > +#include > > +#include > > +#include > > +#include > > +#include > > +#include > > +#include > > +#include > > +#include > > +#include > > +#include > > +#include > > +#include > > + > > +#include > > +#include > > +#include > > +#include > > +#include > > + > > +/********************************* > > +* statistics > > +**********************************/ > > +/* Number of memory pages used by the compressed pool */ > > +static atomic_t zswap_pool_pages = ATOMIC_INIT(0); > > +/* The number of compressed pages currently stored in zswap */ > > +static atomic_t zswap_stored_pages = ATOMIC_INIT(0); > > + > > +/* > > + * The statistics below are not protected from concurrent access for > > + * performance reasons so they may not be a 100% accurate. However, > > + * they do provide useful information on roughly how many times a > > + * certain event is occurring. > > +*/ > > +static u64 zswap_pool_limit_hit; > > +static u64 zswap_written_back_pages; > > +static u64 zswap_reject_reclaim_fail; > > +static u64 zswap_reject_compress_poor; > > +static u64 zswap_reject_alloc_fail; > > +static u64 zswap_reject_kmemcache_fail; > > +static u64 zswap_duplicate_entry; > > + > > +/********************************* > > +* tunables > > +**********************************/ > > +/* Enable/disable zswap (disabled by default, fixed at boot for now) */ > > +static bool zswap_enabled; > > +module_param_named(enabled, zswap_enabled, bool, 0); > > + > > +/* Compressor to be used by zswap (fixed at boot for now) */ > > +#define ZSWAP_COMPRESSOR_DEFAULT "lzo" > > +static char *zswap_compressor = ZSWAP_COMPRESSOR_DEFAULT; > > +module_param_named(compressor, zswap_compressor, charp, 0); > > + > > +/* The maximum percentage of memory that the compressed pool can occupy */ > > +static unsigned int zswap_max_pool_percent = 20; > > +module_param_named(max_pool_percent, > > + zswap_max_pool_percent, uint, 0644); > > + > > I think it's reasonable but... see comments in zbud_reclaim_page(). > > > +/* > > + * Maximum compression ratio, as as percentage, for an acceptable > > + * compressed page. Any pages that do not compress by at least > > + * this ratio will be rejected. > > +*/ > > +static unsigned int zswap_max_compression_ratio = 80; > > +module_param_named(max_compression_ratio, > > + zswap_max_compression_ratio, uint, 0644); > > + > > Prefer not export it, it's hard for use to know what value should set to. True, this is kind of a remnant from zsmalloc. I can remove it. > > > +/********************************* > > +* compression functions > > +**********************************/ > > +/* per-cpu compression transforms */ > > +static struct crypto_comp * __percpu *zswap_comp_pcpu_tfms; > > + > > +enum comp_op { > > + ZSWAP_COMPOP_COMPRESS, > > + ZSWAP_COMPOP_DECOMPRESS > > +}; > > + > > +static int zswap_comp_op(enum comp_op op, const u8 *src, unsigned int slen, > > + u8 *dst, unsigned int *dlen) > > +{ > > + struct crypto_comp *tfm; > > + int ret; > > + > > + tfm = *per_cpu_ptr(zswap_comp_pcpu_tfms, get_cpu()); > > + switch (op) { > > + case ZSWAP_COMPOP_COMPRESS: > > + ret = crypto_comp_compress(tfm, src, slen, dst, dlen); > > + break; > > + case ZSWAP_COMPOP_DECOMPRESS: > > + ret = crypto_comp_decompress(tfm, src, slen, dst, dlen); > > + break; > > + default: > > + ret = -EINVAL; > > + } > > + > > + put_cpu(); > > + return ret; > > +} > > + > > +static int __init zswap_comp_init(void) > > +{ > > + if (!crypto_has_comp(zswap_compressor, 0, 0)) { > > + pr_info("%s compressor not available\n", zswap_compressor); > > + /* fall back to default compressor */ > > + zswap_compressor = ZSWAP_COMPRESSOR_DEFAULT; > > + if (!crypto_has_comp(zswap_compressor, 0, 0)) > > + /* can't even load the default compressor */ > > + return -ENODEV; > > + } > > + pr_info("using %s compressor\n", zswap_compressor); > > + > > + /* alloc percpu transforms */ > > + zswap_comp_pcpu_tfms = alloc_percpu(struct crypto_comp *); > > + if (!zswap_comp_pcpu_tfms) > > + return -ENOMEM; > > + return 0; > > +} > > + > > +static void zswap_comp_exit(void) > > +{ > > + /* free percpu transforms */ > > + if (zswap_comp_pcpu_tfms) > > + free_percpu(zswap_comp_pcpu_tfms); > > +} > > + > > +/********************************* > > +* data structures > > +**********************************/ > > +/* > > + * struct zswap_entry > > + * > > + * This structure contains the metadata for tracking a single compressed > > + * page within zswap. > > + * > > + * rbnode - links the entry into red-black tree for the appropriate swap type > > + * refcount - the number of outstanding reference to the entry. This is needed > > + * to protect against premature freeing of the entry by code > > + * concurent calls to load, invalidate, and writeback. The lock > > + * for the zswap_tree structure that contains the entry must > > + * be held while changing the refcount. Since the lock must > > + * be held, there is no reason to also make refcount atomic. > > + * type - the swap type for the entry. Used to map back to the zswap_tree > > + * structure that contains the entry. > > + * offset - the swap offset for the entry. Index into the red-black tree. > > + * handle - zsmalloc allocation handle that stores the compressed page data > > + * length - the length in bytes of the compressed page data. Needed during > > + * decompression > > The sequence is different from the struct define? Yes, Mel pointed this out too and I forgot to make the change. > > > + */ > > +struct zswap_entry { > > + struct rb_node rbnode; > > + pgoff_t offset; > > + int refcount; > > + unsigned int length; > > + unsigned long handle; > > +}; > > + > > +struct zswap_header { > > + swp_entry_t swpentry; > > +}; > > + > > +/* > > + * The tree lock in the zswap_tree struct protects a few things: > > + * - the rbtree > > + * - the refcount field of each entry in the tree > > + */ > > +struct zswap_tree { > > + struct rb_root rbroot; > > + spinlock_t lock; > > + struct zbud_pool *pool; > > + unsigned type; > > It seems that zswap_tree->type have no usage for zswap. Good catch. Seems that it isn't used anymore. > > > +}; > > + > > +static struct zswap_tree *zswap_trees[MAX_SWAPFILES]; > > + > > +/********************************* > > +* zswap entry functions > > +**********************************/ > > +#define ZSWAP_KMEM_CACHE_NAME "zswap_entry_cache" > > +static struct kmem_cache *zswap_entry_cache; > > + > > +static inline int zswap_entry_cache_create(void) > > +{ > > + zswap_entry_cache = > > + kmem_cache_create(ZSWAP_KMEM_CACHE_NAME, > > + sizeof(struct zswap_entry), 0, 0, NULL); > > + return (zswap_entry_cache == NULL); > > +} > > + > > +static inline void zswap_entry_cache_destory(void) > > +{ > > + kmem_cache_destroy(zswap_entry_cache); > > +} > > + > > +static inline struct zswap_entry *zswap_entry_cache_alloc(gfp_t gfp) > > +{ > > + struct zswap_entry *entry; > > + entry = kmem_cache_alloc(zswap_entry_cache, gfp); > > + if (!entry) > > + return NULL; > > + entry->refcount = 1; > > + return entry; > > +} > > + > > +static inline void zswap_entry_cache_free(struct zswap_entry *entry) > > +{ > > + kmem_cache_free(zswap_entry_cache, entry); > > +} > > + > > +static inline void zswap_entry_get(struct zswap_entry *entry) > > +{ > > + entry->refcount++; > > +} > > + > > +static inline int zswap_entry_put(struct zswap_entry *entry) > > +{ > > + entry->refcount--; > > + return entry->refcount; > > +} > > Better if have lock comments here. will do. > > > + > > +/********************************* > > +* rbtree functions > > +**********************************/ > > +static struct zswap_entry *zswap_rb_search(struct rb_root *root, pgoff_t offset) > > +{ > > + struct rb_node *node = root->rb_node; > > + struct zswap_entry *entry; > > + > > + while (node) { > > + entry = rb_entry(node, struct zswap_entry, rbnode); > > + if (entry->offset > offset) > > + node = node->rb_left; > > + else if (entry->offset < offset) > > + node = node->rb_right; > > + else > > + return entry; > > + } > > + return NULL; > > +} > > + > > +/* > > + * In the case that a entry with the same offset is found, it a pointer to > > + * the existing entry is stored in dupentry and the function returns -EEXIST > > +*/ > > +static int zswap_rb_insert(struct rb_root *root, struct zswap_entry *entry, > > + struct zswap_entry **dupentry) > > +{ > > + struct rb_node **link = &root->rb_node, *parent = NULL; > > + struct zswap_entry *myentry; > > + > > + while (*link) { > > + parent = *link; > > + myentry = rb_entry(parent, struct zswap_entry, rbnode); > > + if (myentry->offset > entry->offset) > > + link = &(*link)->rb_left; > > + else if (myentry->offset < entry->offset) > > + link = &(*link)->rb_right; > > + else { > > + *dupentry = myentry; > > + return -EEXIST; > > + } > > + } > > + rb_link_node(&entry->rbnode, parent, link); > > + rb_insert_color(&entry->rbnode, root); > > + return 0; > > +} > > + > > +/********************************* > > +* per-cpu code > > +**********************************/ > > +static DEFINE_PER_CPU(u8 *, zswap_dstmem); > > + > > +static int __zswap_cpu_notifier(unsigned long action, unsigned long cpu) > > +{ > > + struct crypto_comp *tfm; > > + u8 *dst; > > + > > + switch (action) { > > + case CPU_UP_PREPARE: > > + tfm = crypto_alloc_comp(zswap_compressor, 0, 0); > > + if (IS_ERR(tfm)) { > > + pr_err("can't allocate compressor transform\n"); > > + return NOTIFY_BAD; > > + } > > + *per_cpu_ptr(zswap_comp_pcpu_tfms, cpu) = tfm; > > + dst = kmalloc(PAGE_SIZE * 2, GFP_KERNEL); > > + if (!dst) { > > + pr_err("can't allocate compressor buffer\n"); > > + crypto_free_comp(tfm); > > + *per_cpu_ptr(zswap_comp_pcpu_tfms, cpu) = NULL; > > + return NOTIFY_BAD; > > + } > > + per_cpu(zswap_dstmem, cpu) = dst; > > + break; > > + case CPU_DEAD: > > + case CPU_UP_CANCELED: > > + tfm = *per_cpu_ptr(zswap_comp_pcpu_tfms, cpu); > > + if (tfm) { > > + crypto_free_comp(tfm); > > + *per_cpu_ptr(zswap_comp_pcpu_tfms, cpu) = NULL; > > + } > > + dst = per_cpu(zswap_dstmem, cpu); > > + kfree(dst); > > + per_cpu(zswap_dstmem, cpu) = NULL; > > + break; > > + default: > > + break; > > + } > > + return NOTIFY_OK; > > +} > > + > > +static int zswap_cpu_notifier(struct notifier_block *nb, > > + unsigned long action, void *pcpu) > > +{ > > + unsigned long cpu = (unsigned long)pcpu; > > + return __zswap_cpu_notifier(action, cpu); > > +} > > + > > +static struct notifier_block zswap_cpu_notifier_block = { > > + .notifier_call = zswap_cpu_notifier > > +}; > > + > > +static int zswap_cpu_init(void) > > +{ > > + unsigned long cpu; > > + > > + get_online_cpus(); > > + for_each_online_cpu(cpu) > > + if (__zswap_cpu_notifier(CPU_UP_PREPARE, cpu) != NOTIFY_OK) > > + goto cleanup; > > + register_cpu_notifier(&zswap_cpu_notifier_block); > > + put_online_cpus(); > > + return 0; > > + > > +cleanup: > > + for_each_online_cpu(cpu) > > + __zswap_cpu_notifier(CPU_UP_CANCELED, cpu); > > + put_online_cpus(); > > + return -ENOMEM; > > +} > > + > > +/********************************* > > +* helpers > > +**********************************/ > > +static inline bool zswap_is_full(void) > > +{ > > + int pool_pages = atomic_read(&zswap_pool_pages); > > + return (totalram_pages * zswap_max_pool_percent / 100 < pool_pages); > > +} > > + > > +/* > > + * Carries out the common pattern of freeing and entry's zsmalloc allocation, > > + * freeing the entry itself, and decrementing the number of stored pages. > > + */ > > +static void zswap_free_entry(struct zswap_tree *tree, struct zswap_entry *entry) > > +{ > > + zbud_free(tree->pool, entry->handle); > > + zswap_entry_cache_free(entry); > > + atomic_dec(&zswap_stored_pages); > > + atomic_set(&zswap_pool_pages, zbud_get_pool_size(tree->pool)); > > +} > > + > > +/********************************* > > +* writeback code > > +**********************************/ > > +/* return enum for zswap_get_swap_cache_page */ > > +enum zswap_get_swap_ret { > > + ZSWAP_SWAPCACHE_NEW, > > + ZSWAP_SWAPCACHE_EXIST, > > + ZSWAP_SWAPCACHE_NOMEM > > +}; > > + > > +/* > > + * zswap_get_swap_cache_page > > + * > > + * This is an adaption of read_swap_cache_async() > > + * > > + * This function tries to find a page with the given swap entry > > + * in the swapper_space address space (the swap cache). If the page > > + * is found, it is returned in retpage. Otherwise, a page is allocated, > > + * added to the swap cache, and returned in retpage. > > + * > > + * If success, the swap cache page is returned in retpage > > + * Returns 0 if page was already in the swap cache, page is not locked > > + * Returns 1 if the new page needs to be populated, page is locked > > + * Returns <0 on error > > + */ > > +static int zswap_get_swap_cache_page(swp_entry_t entry, > > + struct page **retpage) > > +{ > > + struct page *found_page, *new_page = NULL; > > + struct address_space *swapper_space = &swapper_spaces[swp_type(entry)]; > > + int err; > > + > > + *retpage = NULL; > > + do { > > + /* > > + * First check the swap cache. Since this is normally > > + * called after lookup_swap_cache() failed, re-calling > > + * that would confuse statistics. > > + */ > > + found_page = find_get_page(swapper_space, entry.val); > > + if (found_page) > > + break; > > + > > + /* > > + * Get a new page to read into from swap. > > + */ > > + if (!new_page) { > > + new_page = alloc_page(GFP_KERNEL); > > + if (!new_page) > > + break; /* Out of memory */ > > + } > > + > > + /* > > + * call radix_tree_preload() while we can wait. > > + */ > > + err = radix_tree_preload(GFP_KERNEL); > > + if (err) > > + break; > > + > > + /* > > + * Swap entry may have been freed since our caller observed it. > > + */ > > + err = swapcache_prepare(entry); > > + if (err == -EEXIST) { /* seems racy */ > > + radix_tree_preload_end(); > > + continue; > > + } > > + if (err) { /* swp entry is obsolete ? */ > > + radix_tree_preload_end(); > > + break; > > + } > > + > > + /* May fail (-ENOMEM) if radix-tree node allocation failed. */ > > + __set_page_locked(new_page); > > + SetPageSwapBacked(new_page); > > + err = __add_to_swap_cache(new_page, entry); > > + if (likely(!err)) { > > + radix_tree_preload_end(); > > + lru_cache_add_anon(new_page); > > + *retpage = new_page; > > + return ZSWAP_SWAPCACHE_NEW; > > + } > > + radix_tree_preload_end(); > > + ClearPageSwapBacked(new_page); > > + __clear_page_locked(new_page); > > + /* > > + * add_to_swap_cache() doesn't return -EEXIST, so we can safely > > + * clear SWAP_HAS_CACHE flag. > > + */ > > + swapcache_free(entry, NULL); > > + } while (err != -ENOMEM); > > + > > + if (new_page) > > + page_cache_release(new_page); > > + if (!found_page) > > + return ZSWAP_SWAPCACHE_NOMEM; > > + *retpage = found_page; > > + return ZSWAP_SWAPCACHE_EXIST; > > +} > > + > > +/* > > + * Attempts to free and entry by adding a page to the swap cache, > > + * decompressing the entry data into the page, and issuing a > > + * bio write to write the page back to the swap device. > > + * > > + * This can be thought of as a "resumed writeback" of the page > > + * to the swap device. We are basically resuming the same swap > > + * writeback path that was intercepted with the frontswap_store() > > + * in the first place. After the page has been decompressed into > > + * the swap cache, the compressed version stored by zswap can be > > + * freed. > > + */ > > +static int zswap_writeback_entry(struct zbud_pool *pool, unsigned long handle) > > +{ > > + struct zswap_header *zhdr; > > + swp_entry_t swpentry; > > + struct zswap_tree *tree; > > + pgoff_t offset; > > + struct zswap_entry *entry; > > + struct page *page; > > + u8 *src, *dst; > > + unsigned int dlen; > > + int ret, refcount; > > + struct writeback_control wbc = { > > + .sync_mode = WB_SYNC_NONE, > > + }; > > + > > + /* extract swpentry from data */ > > + zhdr = zbud_map(pool, handle); > > + swpentry = zhdr->swpentry; /* here */ > > + zbud_unmap(pool, handle); > > + tree = zswap_trees[swp_type(swpentry)]; > > + offset = swp_offset(swpentry); > > + BUG_ON(pool != tree->pool); > > + > > + /* find and ref zswap entry */ > > + spin_lock(&tree->lock); > > + entry = zswap_rb_search(&tree->rbroot, offset); > > + if (!entry) { > > + /* entry was invalidated */ > > + spin_unlock(&tree->lock); > > + return 0; > > + } > > + zswap_entry_get(entry); > > + spin_unlock(&tree->lock); > > + BUG_ON(offset != entry->offset); > > + > > + /* try to allocate swap cache page */ > > + switch (zswap_get_swap_cache_page(swpentry, &page)) { > > + case ZSWAP_SWAPCACHE_NOMEM: /* no memory */ > > + ret = -ENOMEM; > > + goto fail; > > + > > + case ZSWAP_SWAPCACHE_EXIST: /* page is unlocked */ > > + /* page is already in the swap cache, ignore for now */ > > + page_cache_release(page); > > + ret = -EEXIST; > > + goto fail; > > + > > + case ZSWAP_SWAPCACHE_NEW: /* page is locked */ > > + /* decompress */ > > + dlen = PAGE_SIZE; > > + src = (u8 *)zbud_map(tree->pool, entry->handle) + > > + sizeof(struct zswap_header); > > + dst = kmap_atomic(page); > > + ret = zswap_comp_op(ZSWAP_COMPOP_DECOMPRESS, src, > > + entry->length, dst, &dlen); > > + kunmap_atomic(dst); > > + zbud_unmap(tree->pool, entry->handle); > > + BUG_ON(ret); > > + BUG_ON(dlen != PAGE_SIZE); > > + > > + /* page is up to date */ > > + SetPageUptodate(page); > > + } > > + > > + /* start writeback */ > > + SetPageReclaim(page); > > + __swap_writepage(page, &wbc, end_swap_bio_write); > > + page_cache_release(page); > > + zswap_written_back_pages++; > > + > > + spin_lock(&tree->lock); > > + > > + /* drop local reference */ > > + zswap_entry_put(entry); > > + /* drop the initial reference from entry creation */ > > + refcount = zswap_entry_put(entry); > > + > > + /* > > + * There are three possible values for refcount here: > > + * (1) refcount is 1, load is in progress, unlink from rbtree, > > + * load will free > > + * (2) refcount is 0, (normal case) entry is valid, > > + * remove from rbtree and free entry > > + * (3) refcount is -1, invalidate happened during writeback, > > + * free entry > > + */ > > + if (refcount >= 0) { > > + /* no invalidate yet, remove from rbtree */ > > + rb_erase(&entry->rbnode, &tree->rbroot); > > + } > > + spin_unlock(&tree->lock); > > + if (refcount <= 0) { > > + /* free the entry */ > > + zswap_free_entry(tree, entry); > > + return 0; > > + } > > + return -EAGAIN; > > + > > +fail: > > + spin_lock(&tree->lock); > > + zswap_entry_put(entry); > > + spin_unlock(&tree->lock); > > + return ret; > > +} > > + > > +/********************************* > > +* frontswap hooks > > +**********************************/ > > +/* attempts to compress and store an single page */ > > +static int zswap_frontswap_store(unsigned type, pgoff_t offset, > > + struct page *page) > > +{ > > + struct zswap_tree *tree = zswap_trees[type]; > > + struct zswap_entry *entry, *dupentry; > > + int ret; > > + unsigned int dlen = PAGE_SIZE, len; > > + unsigned long handle; > > + char *buf; > > + u8 *src, *dst; > > + struct zswap_header *zhdr; > > + > > + if (!tree) { > > + ret = -ENODEV; > > + goto reject; > > + } > > + > > + /* reclaim space if needed */ > > + if (zswap_is_full()) { > > + zswap_pool_limit_hit++; > > + if (zbud_reclaim_page(tree->pool, 8)) { > > My idea is to wake up a kernel thread here to do the reclaim. > Once zswap is full(20% percent of total mem currently), the kernel > thread should reclaim pages from it. Not only reclaim one page, it > should depend on the current memory pressure. > And then the API in zbud may like this: > zbud_reclaim_page(pool, nr_pages_to_reclaim, nr_retry); So kswapd for zswap. I'm not opposed to the idea if a case can be made for the complexity. I must say, I don't see that case though. The policy can evolve as deficiencies are demonstrated and solutions are found. Can I get your ack on this pending the other changes? Thanks, Seth -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/