Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752991AbaAXOUj (ORCPT ); Fri, 24 Jan 2014 09:20:39 -0500 Received: from mail-ig0-f171.google.com ([209.85.213.171]:50913 "EHLO mail-ig0-f171.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752674AbaAXOUh (ORCPT ); Fri, 24 Jan 2014 09:20:37 -0500 MIME-Version: 1.0 In-Reply-To: References: <20140121050439.GA16664@bbox> <20140121081820.GA31230@bbox> <20140122080238.GD31230@bbox> <20140123030242.GA28732@bbox> Date: Fri, 24 Jan 2014 22:20:36 +0800 Message-ID: Subject: Re: [PATCH v2] mm/zswap: Check all pool pages instead of one pool pages From: Weijie Yang To: Cai Liu Cc: Minchan Kim , Dan Streetman , Seth Jennings , Bob Liu , Cai Liu , Andrew Morton , Linux-MM , Linux-Kernel Content-Type: text/plain; charset=ISO-8859-1 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Jan 23, 2014 at 2:30 PM, Cai Liu wrote: > Hello Minchan > > 2014/1/23 Minchan Kim : >> Hello Cai, >> >> On Thu, Jan 23, 2014 at 09:38:41AM +0800, Cai Liu wrote: >>> Hello Dan >>> >>> 2014/1/22 Dan Streetman : >>> > On Wed, Jan 22, 2014 at 7:16 AM, Cai Liu wrote: >>> >> Hello Minchan >>> >> >>> >> >>> >> 2014/1/22 Minchan Kim >>> >>> >>> >>> Hello Cai, >>> >>> >>> >>> On Tue, Jan 21, 2014 at 09:52:25PM +0800, Cai Liu wrote: >>> >>> > Hello Minchan >>> >>> > >>> >>> > 2014/1/21 Minchan Kim : >>> >>> > > Hello, >>> >>> > > >>> >>> > > On Tue, Jan 21, 2014 at 02:35:07PM +0800, Cai Liu wrote: >>> >>> > >> 2014/1/21 Minchan Kim : >>> >>> > >> > Please check your MUA and don't break thread. >>> >>> > >> > >>> >>> > >> > On Tue, Jan 21, 2014 at 11:07:42AM +0800, Cai Liu wrote: >>> >>> > >> >> Thanks for your review. >>> >>> > >> >> >>> >>> > >> >> 2014/1/21 Minchan Kim : >>> >>> > >> >> > Hello Cai, >>> >>> > >> >> > >>> >>> > >> >> > On Mon, Jan 20, 2014 at 03:50:18PM +0800, Cai Liu wrote: >>> >>> > >> >> >> zswap can support multiple swapfiles. So we need to check >>> >>> > >> >> >> all zbud pool pages in zswap. >>> >>> > >> >> >> >>> >>> > >> >> >> Version 2: >>> >>> > >> >> >> * add *total_zbud_pages* in zbud to record all the pages in pools >>> >>> > >> >> >> * move the updating of pool pages statistics to >>> >>> > >> >> >> alloc_zbud_page/free_zbud_page to hide the details >>> >>> > >> >> >> >>> >>> > >> >> >> Signed-off-by: Cai Liu >>> >>> > >> >> >> --- >>> >>> > >> >> >> include/linux/zbud.h | 2 +- >>> >>> > >> >> >> mm/zbud.c | 44 ++++++++++++++++++++++++++++++++------------ >>> >>> > >> >> >> mm/zswap.c | 4 ++-- >>> >>> > >> >> >> 3 files changed, 35 insertions(+), 15 deletions(-) >>> >>> > >> >> >> >>> >>> > >> >> >> diff --git a/include/linux/zbud.h b/include/linux/zbud.h >>> >>> > >> >> >> index 2571a5c..1dbc13e 100644 >>> >>> > >> >> >> --- a/include/linux/zbud.h >>> >>> > >> >> >> +++ b/include/linux/zbud.h >>> >>> > >> >> >> @@ -17,6 +17,6 @@ void zbud_free(struct zbud_pool *pool, unsigned long handle); >>> >>> > >> >> >> int zbud_reclaim_page(struct zbud_pool *pool, unsigned int retries); >>> >>> > >> >> >> void *zbud_map(struct zbud_pool *pool, unsigned long handle); >>> >>> > >> >> >> void zbud_unmap(struct zbud_pool *pool, unsigned long handle); >>> >>> > >> >> >> -u64 zbud_get_pool_size(struct zbud_pool *pool); >>> >>> > >> >> >> +u64 zbud_get_pool_size(void); >>> >>> > >> >> >> >>> >>> > >> >> >> #endif /* _ZBUD_H_ */ >>> >>> > >> >> >> diff --git a/mm/zbud.c b/mm/zbud.c >>> >>> > >> >> >> index 9451361..711aaf4 100644 >>> >>> > >> >> >> --- a/mm/zbud.c >>> >>> > >> >> >> +++ b/mm/zbud.c >>> >>> > >> >> >> @@ -52,6 +52,13 @@ >>> >>> > >> >> >> #include >>> >>> > >> >> >> #include >>> >>> > >> >> >> >>> >>> > >> >> >> +/********************************* >>> >>> > >> >> >> +* statistics >>> >>> > >> >> >> +**********************************/ >>> >>> > >> >> >> + >>> >>> > >> >> >> +/* zbud pages in all pools */ >>> >>> > >> >> >> +static u64 total_zbud_pages; >>> >>> > >> >> >> + >>> >>> > >> >> >> /***************** >>> >>> > >> >> >> * Structures >>> >>> > >> >> >> *****************/ >>> >>> > >> >> >> @@ -142,10 +149,28 @@ static struct zbud_header *init_zbud_page(struct page *page) >>> >>> > >> >> >> return zhdr; >>> >>> > >> >> >> } >>> >>> > >> >> >> >>> >>> > >> >> >> +static struct page *alloc_zbud_page(struct zbud_pool *pool, gfp_t gfp) >>> >>> > >> >> >> +{ >>> >>> > >> >> >> + struct page *page; >>> >>> > >> >> >> + >>> >>> > >> >> >> + page = alloc_page(gfp); >>> >>> > >> >> >> + >>> >>> > >> >> >> + if (page) { >>> >>> > >> >> >> + pool->pages_nr++; >>> >>> > >> >> >> + total_zbud_pages++; >>> >>> > >> >> > >>> >>> > >> >> > Who protect race? >>> >>> > >> >> >>> >>> > >> >> Yes, here the pool->pages_nr and also the total_zbud_pages are not protected. >>> >>> > >> >> I will re-do it. >>> >>> > >> >> >>> >>> > >> >> I will change *total_zbud_pages* to atomic type. >>> >>> > >> > >>> >>> > >> > Wait, it doesn't make sense. Now, you assume zbud allocator would be used >>> >>> > >> > for only zswap. It's true until now but we couldn't make sure it in future. >>> >>> > >> > If other user start to use zbud allocator, total_zbud_pages would be pointless. >>> >>> > >> >>> >>> > >> Yes, you are right. ZBUD is a common module. So in this patch calculate the >>> >>> > >> zswap pool size in zbud is not suitable. >>> >>> > >> >>> >>> > >> > >>> >>> > >> > Another concern is that what's your scenario for above two swap? >>> >>> > >> > How often we need to call zbud_get_pool_size? >>> >>> > >> > In previous your patch, you reduced the number of call so IIRC, >>> >>> > >> > we only called it in zswap_is_full and for debugfs. >>> >>> > >> >>> >>> > >> zbud_get_pool_size() is called frequently when adding/freeing zswap >>> >>> > >> entry happen in zswap . This is why in this patch I added a counter in zbud, >>> >>> > >> and then in zswap the iteration of zswap_list to calculate the pool size will >>> >>> > >> not be needed. >>> >>> > > >>> >>> > > We can remove updating zswap_pool_pages in zswap_frontswap_store and >>> >>> > > zswap_free_entry as I said. So zswap_is_full is only hot spot. >>> >>> > > Do you think it's still big overhead? Why? Maybe locking to prevent >>> >>> > > destroying? Then, we can use RCU to minimize the overhead as I mentioned. >>> >>> > >>> >>> > I get your point. Yes, In my previous patch, zswap_is_full() was the >>> >>> > only path to call >>> >>> > zbud_get_pool_size(). And your suggestion on patch v1 to remove the unnecessary >>> >>> > iteration will reduce the overhead further. >>> >>> > >>> >>> > So adding the calculating of all the pool size in zswap.c is better. >>> >>> > >>> >>> > >> >>> >>> > >> > Of course, it would need some lock or refcount to prevent destroy >>> >>> > >> > of zswap_tree in parallel with zswap_frontswap_invalidate_area but >>> >>> > >> > zswap_is_full doesn't need to be exact so RCU would be good fit. >>> >>> > >> > >>> >>> > >> > Most important point is that now zswap doesn't consider multiple swap. >>> >>> > >> > For example, Let's assume you uses two swap A and B with different priority >>> >>> > >> > and A already has charged 19% long time ago and let's assume that A swap is >>> >>> > >> > full now so VM start to use B so that B has charged 1% recently. >>> >>> > >> > It menas zswap charged (19% + 1%)i is full by default. >>> >>> > >> > >>> >>> > >> > Then, if VM want to swap out more pages into B, zbud_reclaim_page >>> >>> > >> > would be evict one of pages in B's pool and it would be repeated >>> >>> > >> > continuously. It's totally LRU reverse problem and swap thrashing in B >>> >>> > >> > would happen. >>> >>> > >> > >>> >>> > >> >>> >>> > >> The scenario is below: >>> >>> > >> There are 2 swap A, B in system. If pool size of A reach 19% of ram >>> >>> > >> size and swap A >>> >>> > >> is also full. Then swap B will be used. Pool size of B will be >>> >>> > >> increased until it hit >>> >>> > >> the 20% of the ram size. By now zswap pool size is about 39% of ram size. >>> >>> > >> If there are more than 2 swap file/device, zswap pool will expand out >>> >>> > >> of control >>> >>> > >> and there may be no swapout happened. >>> >>> > > >>> >>> > > I know. >>> >>> > > >>> >>> > >> >>> >>> > >> I think the original intention of zswap designer is to keep the total >>> >>> > >> zswap pools size below >>> >>> > >> 20% of RAM size. >>> >>> > > >>> >>> > > My point is your patch still doesn't solve the example I mentioned. >>> >>> > >>> >>> > Hmm. My patch only make sure all the zswap pools use maximum 20% of >>> >>> > RAM size. It is a new problem in your example. The zbud_reclaim_page would >>> >>> > not swap out the oldest zbud page when multiple swaps are used. >>> >>> > >>> >>> > Maybe the new problem can be resolved in another patch. >>> >>> >>> >>> It means current zswap has a problem in multiple swap but you want >>> >>> to fix a problem which happens only when it is used for multiple swap. >>> >>> So, I'm not sure we want a fix in this phase before discussing more >>> >>> fundamental thing. >>> >>> >>> >> >>> >> Yes, The bug which I want to fix only happens when multiple swap are used. >>> >> >>> >>> That's why I want to know why you want to use multiple swap with zswap >>> >>> but you are never saying it to us. :( >>> >>> >>> >> >>> >> If user uses more than one swap device/file, then this is an issue. >>> >> Zswap pool is created when a swap device/file is swapped on happens. >>> >> So there will be more than one zswap pool when user uses 2 or even >>> >> more swap devices/files. >>> >> >>> >> I am not sure whether multiple swap are popular. But if multiple swap >>> >> are swapped >>> >> on, then multiple zswap pool will be created. And the size of these pools may >>> >> out of control. >>> > >>> > Personally I don't think using multiple swap partitions/files has to >>> > be popular to need to solve this, it only needs to be possible, which >>> > it is. >>> > >>> > Why not just leave zbud unchanged, and sum up the total size using a >>> > list of active zswap_trees as Minchan suggested for the v1 patch? The >>> >>> Yes. This is what I want to do in the v3 patch after this bug is considered need >>> to be fixed. >> >> In my position, I'd like to fix zswap and multiple swap problem firstly >> and like the Weijie's suggestion. >> >> So, how about this? >> I didn't look at code in detail and want to show the concept. > > I read the RFC patch. I think it's perfect. > >> That's why I added RFC tag. >> >> From 67c64746e977a091ee30ca37bbc034990adf5ca5 Mon Sep 17 00:00:00 2001 >> From: Minchan Kim >> Date: Thu, 23 Jan 2014 11:41:44 +0900 >> Subject: [RFC] zswap: support multiple swap >> >> Cai Liu reporeted that now zbud pool pages counting has a problem >> when multiple swap is used because it just counts one of swap >> among mutliple swap intead of all of swap so zswap cannot control >> writeback properly. The result is unnecessary writeback or >> no writeback when we should really writeback. IOW, it made zswap >> crazy. >> >> Another problem in zswap is following as. >> For example, let's assume we use two swap A and B with different >> priority and A already has charged 19% long time ago and let's assume >> that A swap is full now so VM start to use B so that B has charged 1% >> recently. It menas zswap charged (19% + 1%) is full by default. >> Then, if VM want to swap out more pages into B, zbud_reclaim_page >> would be evict one of pages in B's pool and it would be repeated >> continuously. It's totally LRU reverse problem and swap thrashing >> in B would happen. >> >> This patch makes zswap consider mutliple swap by creating *a* zbud >> pool which will be shared by multiple swap so all of zswap pages >> in multiple swap keep order by LRU so it can prevent above two >> problems. >> >> Reported-by: Cai Liu >> Suggested-by: Weijie Yang >> Signed-off-by: Minchan Kim >> --- >> mm/zswap.c | 56 +++++++++++++++++++++++++++++--------------------------- >> 1 file changed, 29 insertions(+), 27 deletions(-) Hi, Minchan I reviewed this patch, it is good to me. Just have a little nitpick, see below. Regards >> diff --git a/mm/zswap.c b/mm/zswap.c >> index 5a63f78a5601..96039e86db79 100644 >> --- a/mm/zswap.c >> +++ b/mm/zswap.c >> @@ -89,6 +89,8 @@ static unsigned int zswap_max_pool_percent = 20; >> module_param_named(max_pool_percent, >> zswap_max_pool_percent, uint, 0644); >> >> +static struct zbud_pool *mem_pool; >> + nitpick1: I'd like to put the same logical code together. such as put this mem_pool definition with zswap_trees and zswap_entry_cache Just my oddity, of course you can ignore it. >> /********************************* >> * compression functions >> **********************************/ >> @@ -189,7 +191,6 @@ struct zswap_header { >> struct zswap_tree { >> struct rb_root rbroot; >> spinlock_t lock; >> - struct zbud_pool *pool; >> }; >> >> static struct zswap_tree *zswap_trees[MAX_SWAPFILES]; >> @@ -288,10 +289,10 @@ static void zswap_rb_erase(struct rb_root *root, struct zswap_entry *entry) >> static void zswap_free_entry(struct zswap_tree *tree, >> struct zswap_entry *entry) nitpick2: How about remove the tree parameter in zswap_free_entry? >> { >> - zbud_free(tree->pool, entry->handle); >> + zbud_free(mem_pool, entry->handle); >> zswap_entry_cache_free(entry); >> atomic_dec(&zswap_stored_pages); >> - zswap_pool_pages = zbud_get_pool_size(tree->pool); >> + zswap_pool_pages = zbud_get_pool_size(mem_pool); >> } >> >> /* caller must hold the tree lock */ >> @@ -545,7 +546,7 @@ static int zswap_writeback_entry(struct zbud_pool *pool, unsigned long handle) >> zbud_unmap(pool, handle); >> tree = zswap_trees[swp_type(swpentry)]; >> offset = swp_offset(swpentry); >> - BUG_ON(pool != tree->pool); >> + BUG_ON(pool != mem_pool); >> >> /* find and ref zswap entry */ >> spin_lock(&tree->lock); >> @@ -573,13 +574,13 @@ static int zswap_writeback_entry(struct zbud_pool *pool, unsigned long handle) >> case ZSWAP_SWAPCACHE_NEW: /* page is locked */ >> /* decompress */ >> dlen = PAGE_SIZE; >> - src = (u8 *)zbud_map(tree->pool, entry->handle) + >> + src = (u8 *)zbud_map(mem_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); >> + zbud_unmap(mem_pool, entry->handle); >> BUG_ON(ret); >> BUG_ON(dlen != PAGE_SIZE); >> >> @@ -652,7 +653,7 @@ static int zswap_frontswap_store(unsigned type, pgoff_t offset, >> /* reclaim space if needed */ >> if (zswap_is_full()) { >> zswap_pool_limit_hit++; >> - if (zbud_reclaim_page(tree->pool, 8)) { >> + if (zbud_reclaim_page(mem_pool, 8)) { >> zswap_reject_reclaim_fail++; >> ret = -ENOMEM; >> goto reject; >> @@ -679,7 +680,7 @@ static int zswap_frontswap_store(unsigned type, pgoff_t offset, >> >> /* store */ >> len = dlen + sizeof(struct zswap_header); >> - ret = zbud_alloc(tree->pool, len, __GFP_NORETRY | __GFP_NOWARN, >> + ret = zbud_alloc(mem_pool, len, __GFP_NORETRY | __GFP_NOWARN, >> &handle); >> if (ret == -ENOSPC) { >> zswap_reject_compress_poor++; >> @@ -689,11 +690,11 @@ static int zswap_frontswap_store(unsigned type, pgoff_t offset, >> zswap_reject_alloc_fail++; >> goto freepage; >> } >> - zhdr = zbud_map(tree->pool, handle); >> + zhdr = zbud_map(mem_pool, handle); >> zhdr->swpentry = swp_entry(type, offset); >> buf = (u8 *)(zhdr + 1); >> memcpy(buf, dst, dlen); >> - zbud_unmap(tree->pool, handle); >> + zbud_unmap(mem_pool, handle); >> put_cpu_var(zswap_dstmem); >> >> /* populate entry */ >> @@ -716,7 +717,7 @@ static int zswap_frontswap_store(unsigned type, pgoff_t offset, >> >> /* update stats */ >> atomic_inc(&zswap_stored_pages); >> - zswap_pool_pages = zbud_get_pool_size(tree->pool); >> + zswap_pool_pages = zbud_get_pool_size(mem_pool); >> >> return 0; >> >> @@ -752,13 +753,13 @@ static int zswap_frontswap_load(unsigned type, pgoff_t offset, >> >> /* decompress */ >> dlen = PAGE_SIZE; >> - src = (u8 *)zbud_map(tree->pool, entry->handle) + >> + src = (u8 *)zbud_map(mem_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); >> + zbud_unmap(mem_pool, entry->handle); >> BUG_ON(ret); >> >> spin_lock(&tree->lock); >> @@ -807,8 +808,6 @@ static void zswap_frontswap_invalidate_area(unsigned type) >> zswap_free_entry(tree, entry); >> tree->rbroot = RB_ROOT; >> spin_unlock(&tree->lock); >> - >> - zbud_destroy_pool(tree->pool); >> kfree(tree); >> zswap_trees[type] = NULL; >> } >> @@ -822,20 +821,14 @@ static void zswap_frontswap_init(unsigned type) >> struct zswap_tree *tree; >> >> tree = kzalloc(sizeof(struct zswap_tree), GFP_KERNEL); >> - if (!tree) >> - goto err; >> - tree->pool = zbud_create_pool(GFP_KERNEL, &zswap_zbud_ops); >> - if (!tree->pool) >> - goto freetree; >> + if (!tree) { >> + pr_err("alloc failed, zswap disabled for swap type %d\n", type); >> + return; >> + } >> + >> tree->rbroot = RB_ROOT; >> spin_lock_init(&tree->lock); >> zswap_trees[type] = tree; >> - return; >> - >> -freetree: >> - kfree(tree); >> -err: >> - pr_err("alloc failed, zswap disabled for swap type %d\n", type); >> } >> >> static struct frontswap_ops zswap_frontswap_ops = { >> @@ -907,9 +900,14 @@ static int __init init_zswap(void) >> return 0; >> >> pr_info("loading zswap\n"); >> + >> + mem_pool = zbud_create_pool(GFP_KERNEL, &zswap_zbud_ops); >> + if (!mem_pool) >> + goto error; >> + >> if (zswap_entry_cache_create()) { >> pr_err("entry cache creation failed\n"); >> - goto error; >> + goto cachefail; >> } >> if (zswap_comp_init()) { >> pr_err("compressor initialization failed\n"); >> @@ -919,6 +917,8 @@ static int __init init_zswap(void) >> pr_err("per-cpu initialization failed\n"); >> goto pcpufail; >> } >> + >> + >> frontswap_register_ops(&zswap_frontswap_ops); >> if (zswap_debugfs_init()) >> pr_warn("debugfs initialization failed\n"); >> @@ -927,6 +927,8 @@ pcpufail: >> zswap_comp_exit(); >> compfail: >> zswap_entry_cache_destory(); >> +cachefail: >> + zbud_destroy_pool(mem_pool); >> error: >> return -ENOMEM; >> } >> -- >> 1.8.5.2 >> >> >> -- >> Kind regards, >> Minchan Kim -- 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/