Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753665AbaAUGfO (ORCPT ); Tue, 21 Jan 2014 01:35:14 -0500 Received: from mail-qa0-f48.google.com ([209.85.216.48]:33820 "EHLO mail-qa0-f48.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753578AbaAUGfJ (ORCPT ); Tue, 21 Jan 2014 01:35:09 -0500 MIME-Version: 1.0 In-Reply-To: <20140121050439.GA16664@bbox> References: <20140121050439.GA16664@bbox> Date: Tue, 21 Jan 2014 14:35:07 +0800 Message-ID: Subject: Re: [PATCH v2] mm/zswap: Check all pool pages instead of one pool pages From: Cai Liu To: Minchan Kim Cc: 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 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. > 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 think the original intention of zswap designer is to keep the total zswap pools size below 20% of RAM size. Thanks. > Please say your usecase scenario and if it's really problem, > we need more surgery. > > Thanks. > >> For *pool->pages_nr*, one way is to use pool->lock to protect. But I >> think it is too heavy. >> So does it ok to change pages_nr to atomic type too? >> >> >> > >> >> + } >> >> + >> >> + return page; >> >> +} >> >> + >> >> + >> >> /* Resets the struct page fields and frees the page */ >> >> -static void free_zbud_page(struct zbud_header *zhdr) >> >> +static void free_zbud_page(struct zbud_pool *pool, struct zbud_header *zhdr) >> >> { >> >> __free_page(virt_to_page(zhdr)); >> >> + >> >> + pool->pages_nr--; >> >> + total_zbud_pages--; >> >> } >> >> >> >> /* >> >> @@ -279,11 +304,10 @@ int zbud_alloc(struct zbud_pool *pool, int size, gfp_t gfp, >> >> >> >> /* Couldn't find unbuddied zbud page, create new one */ >> >> spin_unlock(&pool->lock); >> >> - page = alloc_page(gfp); >> >> + page = alloc_zbud_page(pool, gfp); >> >> if (!page) >> >> return -ENOMEM; >> >> spin_lock(&pool->lock); >> >> - pool->pages_nr++; >> >> zhdr = init_zbud_page(page); >> >> bud = FIRST; >> >> >> >> @@ -349,8 +373,7 @@ void zbud_free(struct zbud_pool *pool, unsigned long handle) >> >> if (zhdr->first_chunks == 0 && zhdr->last_chunks == 0) { >> >> /* zbud page is empty, free */ >> >> list_del(&zhdr->lru); >> >> - free_zbud_page(zhdr); >> >> - pool->pages_nr--; >> >> + free_zbud_page(pool, zhdr); >> >> } else { >> >> /* Add to unbuddied list */ >> >> freechunks = num_free_chunks(zhdr); >> >> @@ -447,8 +470,7 @@ next: >> >> * Both buddies are now free, free the zbud page and >> >> * return success. >> >> */ >> >> - free_zbud_page(zhdr); >> >> - pool->pages_nr--; >> >> + free_zbud_page(pool, zhdr); >> >> spin_unlock(&pool->lock); >> >> return 0; >> >> } else if (zhdr->first_chunks == 0 || >> >> @@ -496,14 +518,12 @@ void zbud_unmap(struct zbud_pool *pool, unsigned long handle) >> >> >> >> /** >> >> * zbud_get_pool_size() - gets the zbud pool size in pages >> >> - * @pool: pool whose size is being queried >> >> * >> >> - * Returns: size in pages of the given pool. The pool lock need not be >> >> - * taken to access pages_nr. >> >> + * Returns: size in pages of all the zbud pools. >> >> */ >> >> -u64 zbud_get_pool_size(struct zbud_pool *pool) >> >> +u64 zbud_get_pool_size(void) >> >> { >> >> - return pool->pages_nr; >> >> + return total_zbud_pages; >> >> } >> >> >> >> static int __init init_zbud(void) >> >> diff --git a/mm/zswap.c b/mm/zswap.c >> >> index 5a63f78..ef44d9d 100644 >> >> --- a/mm/zswap.c >> >> +++ b/mm/zswap.c >> >> @@ -291,7 +291,7 @@ static void zswap_free_entry(struct zswap_tree *tree, >> >> zbud_free(tree->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(); >> >> } >> >> >> >> /* caller must hold the tree lock */ >> >> @@ -716,7 +716,7 @@ 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(); >> >> >> >> return 0; >> >> >> >> -- >> >> 1.7.10.4 >> >> >> >> -- >> >> To unsubscribe, send a message with 'unsubscribe linux-mm' in >> >> the body to majordomo@kvack.org. For more info on Linux MM, >> >> see: http://www.linux-mm.org/ . >> >> Don't email: email@kvack.org >> > >> > -- >> > Kind regards, >> > Minchan Kim >> >> -- >> To unsubscribe, send a message with 'unsubscribe linux-mm' in >> the body to majordomo@kvack.org. For more info on Linux MM, >> see: http://www.linux-mm.org/ . >> Don't email: email@kvack.org > > -- > 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/