Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754180AbdC1Fcx (ORCPT ); Tue, 28 Mar 2017 01:32:53 -0400 Received: from mga06.intel.com ([134.134.136.31]:5482 "EHLO mga06.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754010AbdC1Fcq (ORCPT ); Tue, 28 Mar 2017 01:32:46 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.36,235,1486454400"; d="scan'208";a="1147757254" From: "Huang, Ying" To: Andrew Morton Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, Huang Ying Subject: [PATCH -mm -v7 9/9] mm, THP, swap: Delay splitting THP during swap out Date: Tue, 28 Mar 2017 13:32:09 +0800 Message-Id: <20170328053209.25876-10-ying.huang@intel.com> X-Mailer: git-send-email 2.11.0 In-Reply-To: <20170328053209.25876-1-ying.huang@intel.com> References: <20170328053209.25876-1-ying.huang@intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 6193 Lines: 173 From: Huang Ying In this patch, splitting huge page is delayed from almost the first step of swapping out to after allocating the swap space for the THP (Transparent Huge Page) and adding the THP into the swap cache. This will reduce lock acquiring/releasing for the locks used for the swap cache management. This is the first step for the THP swap support. The plan is to delay splitting the THP step by step and avoid splitting the THP finally. The advantages of the THP swap support include: - Batch the swap operations for the THP to reduce lock acquiring/releasing, including allocating/freeing the swap space, adding/deleting to/from the swap cache, and writing/reading the swap space, etc. This will help to improve the THP swap performance. - The THP swap space read/write will be 2M sequential IO. It is particularly helpful for the swap read, which usually are 4k random IO. This will help to improve the THP swap performance too. - It will help the memory fragmentation, especially when the THP is heavily used by the applications. The 2M continuous pages will be free up after the THP swapping out. - It will improve the THP utilization on the system with the swap turned on. Because the speed for khugepaged to collapse the normal pages into the THP is quite slow. After the THP is split during the swapping out, it will take quite long time for the normal pages to collapse back into the THP after being swapped in. The high THP utilization helps the efficiency of the page based memory management too. There are some concerns regarding THP swap in, mainly because possible enlarged read/write IO size (for swap in/out) may put more overhead on the storage device. To deal with that, the THP swap in should be turned on only when necessary. For example, it can be selected via "always/never/madvise" logic, to be turned on globally, turned off globally, or turned on only for VMA with MADV_HUGEPAGE, etc. With the patchset, the swap out throughput improves 14.9% (from about 3.77GB/s to about 4.34GB/s) in the vm-scalability swap-w-seq test case with 8 processes. The test is done on a Xeon E5 v3 system. The swap device used is a RAM simulated PMEM (persistent memory) device. To test the sequential swapping out, the test case creates 8 processes, which sequentially allocate and write to the anonymous pages until the RAM and part of the swap device is used up. The detailed comparison result is as follow, base base+patchset ---------------- -------------------------- %stddev %change %stddev \ | \ 7043990 ± 0% +21.2% 8536807 ± 0% vm-scalability.throughput 109.94 ± 1% -16.2% 92.09 ± 0% vm-scalability.time.elapsed_time 3957091 ± 0% +14.9% 4547173 ± 0% vmstat.swap.so 31.46 ± 1% -38.3% 19.42 ± 0% perf-stat.cache-miss-rate% 1.04 ± 1% +22.2% 1.27 ± 0% perf-stat.ipc 9.33 ± 2% -60.7% 3.67 ± 1% perf-profile.calltrace.cycles-pp.add_to_swap.shrink_page_list.shrink_inactive_list.shrink_node_memcg.shrink_node Signed-off-by: "Huang, Ying" --- mm/swap_state.c | 60 ++++++++++++++++++++++++++++++++++++++++++++++++++++++--- 1 file changed, 57 insertions(+), 3 deletions(-) diff --git a/mm/swap_state.c b/mm/swap_state.c index 504f67d73f67..6d63ff703d39 100644 --- a/mm/swap_state.c +++ b/mm/swap_state.c @@ -19,6 +19,7 @@ #include #include #include +#include #include @@ -183,12 +184,53 @@ void __delete_from_swap_cache(struct page *page) ADD_CACHE_INFO(del_total, nr); } +#ifdef CONFIG_THP_SWAP_CLUSTER +int add_to_swap_trans_huge(struct page *page, struct list_head *list) +{ + swp_entry_t entry; + int ret = 0; + + /* cannot split, which may be needed during swap in, skip it */ + if (!can_split_huge_page(page, NULL)) + return -EBUSY; + /* fallback to split huge page firstly if no PMD map */ + if (!compound_mapcount(page)) + return 0; + entry = get_huge_swap_page(); + if (!entry.val) + return 0; + if (mem_cgroup_try_charge_swap(page, entry, HPAGE_PMD_NR)) { + __swapcache_free(entry, true); + return -EOVERFLOW; + } + ret = add_to_swap_cache(page, entry, + __GFP_HIGH | __GFP_NOMEMALLOC|__GFP_NOWARN); + /* -ENOMEM radix-tree allocation failure */ + if (ret) { + __swapcache_free(entry, true); + return 0; + } + ret = split_huge_page_to_list(page, list); + if (ret) { + delete_from_swap_cache(page); + return -EBUSY; + } + return 1; +} +#else +static inline int add_to_swap_trans_huge(struct page *page, + struct list_head *list) +{ + return 0; +} +#endif + /** * add_to_swap - allocate swap space for a page * @page: page we want to move to swap * * Allocate swap space for the page and add the page to the - * swap cache. Caller needs to hold the page lock. + * swap cache. Caller needs to hold the page lock. */ int add_to_swap(struct page *page, struct list_head *list) { @@ -198,6 +240,18 @@ int add_to_swap(struct page *page, struct list_head *list) VM_BUG_ON_PAGE(!PageLocked(page), page); VM_BUG_ON_PAGE(!PageUptodate(page), page); + if (unlikely(PageTransHuge(page))) { + err = add_to_swap_trans_huge(page, list); + switch (err) { + case 1: + return 1; + case 0: + /* fallback to split firstly if return 0 */ + break; + default: + return 0; + } + } entry = get_swap_page(); if (!entry.val) return 0; @@ -315,7 +369,7 @@ struct page * lookup_swap_cache(swp_entry_t entry) page = find_get_page(swap_address_space(entry), swp_offset(entry)); - if (page) { + if (page && likely(!PageTransCompound(page))) { INC_CACHE_INFO(find_success); if (TestClearPageReadahead(page)) atomic_inc(&swapin_readahead_hits); @@ -526,7 +580,7 @@ struct page *swapin_readahead(swp_entry_t entry, gfp_t gfp_mask, gfp_mask, vma, addr); if (!page) continue; - if (offset != entry_offset) + if (offset != entry_offset && likely(!PageTransCompound(page))) SetPageReadahead(page); put_page(page); } -- 2.11.0