Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S936600Ab3DIVuL (ORCPT ); Tue, 9 Apr 2013 17:50:11 -0400 Received: from e28smtp09.in.ibm.com ([122.248.162.9]:38719 "EHLO e28smtp09.in.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S936462Ab3DIVuI (ORCPT ); Tue, 9 Apr 2013 17:50:08 -0400 From: "Srivatsa S. Bhat" Subject: [RFC PATCH v2 07/15] mm: Add an optimized version of del_from_freelist to keep page allocation fast To: akpm@linux-foundation.org, mgorman@suse.de, matthew.garrett@nebula.com, dave@sr71.net, rientjes@google.com, riel@redhat.com, arjan@linux.intel.com, srinivas.pandruvada@linux.intel.com, maxime.coquelin@stericsson.com, loic.pallardy@stericsson.com, kamezawa.hiroyu@jp.fujitsu.com, lenb@kernel.org, rjw@sisk.pl Cc: gargankita@gmail.com, paulmck@linux.vnet.ibm.com, amit.kachhap@linaro.org, svaidy@linux.vnet.ibm.com, andi@firstfloor.org, wujianguo@huawei.com, kmpark@infradead.org, thomas.abraham@linaro.org, santosh.shilimkar@ti.com, srivatsa.bhat@linux.vnet.ibm.com, linux-pm@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org Date: Wed, 10 Apr 2013 03:17:19 +0530 Message-ID: <20130409214717.4500.34638.stgit@srivatsabhat.in.ibm.com> In-Reply-To: <20130409214443.4500.44168.stgit@srivatsabhat.in.ibm.com> References: <20130409214443.4500.44168.stgit@srivatsabhat.in.ibm.com> User-Agent: StGIT/0.14.3 MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit X-TM-AS-MML: No X-Content-Scanned: Fidelis XPS MAILER x-cbid: 13040921-2674-0000-0000-00000888B271 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 5580 Lines: 171 One of the main advantages of this design of memory regions is that page allocations can potentially be extremely fast - almost with no extra overhead from memory regions. To exploit that, introduce an optimized version of del_from_freelist(), which utilizes the fact that we always delete items from the head of the list during page allocation. Basically, we want to keep a note of the region from which we are allocating in a given freelist, to avoid having to compute the page-to-zone-region for every page allocation. So introduce a 'next_region' pointer in every freelist to achieve that, and use it to keep the fastpath of page allocation almost as fast as it would have been without memory regions. Signed-off-by: Srivatsa S. Bhat --- include/linux/mm.h | 14 +++++++++++ include/linux/mmzone.h | 6 +++++ mm/page_alloc.c | 62 +++++++++++++++++++++++++++++++++++++++++++++++- 3 files changed, 81 insertions(+), 1 deletion(-) diff --git a/include/linux/mm.h b/include/linux/mm.h index dff478b..cb0d898 100644 --- a/include/linux/mm.h +++ b/include/linux/mm.h @@ -741,6 +741,20 @@ static inline int page_zone_region_id(const struct page *page) return pgdat->node_regions[node_region_idx].zone_region_idx[z_num]; } +static inline void set_next_region_in_freelist(struct free_list *free_list) +{ + struct page *page; + int region_id; + + if (unlikely(list_empty(&free_list->list))) { + free_list->next_region = NULL; + } else { + page = list_entry(free_list->list.next, struct page, lru); + region_id = page_zone_region_id(page); + free_list->next_region = &free_list->mr_list[region_id]; + } +} + #ifdef SECTION_IN_PAGE_FLAGS static inline void set_page_section(struct page *page, unsigned long section) { diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h index 76667bf..d8d67fc 100644 --- a/include/linux/mmzone.h +++ b/include/linux/mmzone.h @@ -92,6 +92,12 @@ struct free_list { struct list_head list; /* + * Pointer to the region from which the next allocation will be + * satisfied. (Same as the freelist's first pageblock's region.) + */ + struct mem_region_list *next_region; /* for fast page allocation */ + + /* * Demarcates pageblocks belonging to different regions within * this freelist. */ diff --git a/mm/page_alloc.c b/mm/page_alloc.c index 7fb4254..a68174c 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -539,6 +539,15 @@ static void add_to_freelist(struct page *page, struct free_list *free_list) /* This is the first region, so add to the head of the list */ prev_region_list = &free_list->list; +#ifdef CONFIG_DEBUG_PAGEALLOC + WARN((list_empty(&free_list->list) && free_list->next_region != NULL), + "%s: next_region not NULL\n", __func__); +#endif + /* + * Set 'next_region' to this region, since this is the first region now + */ + free_list->next_region = region; + out: list_add(lru, prev_region_list); @@ -546,6 +555,47 @@ out: region->page_block = lru; } +/** + * __rmqueue_smallest() *always* deletes elements from the head of the + * list. Use this knowledge to keep page allocation fast, despite being + * region-aware. + * + * Do *NOT* call this function if you are deleting from somewhere deep + * inside the freelist. + */ +static void rmqueue_del_from_freelist(struct page *page, + struct free_list *free_list) +{ + struct list_head *lru = &page->lru; + +#ifdef CONFIG_DEBUG_PAGEALLOC + WARN((free_list->list.next != lru), + "%s: page not at head of list", __func__); +#endif + + list_del(lru); + + /* Fastpath */ + if (--(free_list->next_region->nr_free)) { + +#ifdef CONFIG_DEBUG_PAGEALLOC + WARN(free_list->next_region->nr_free < 0, + "%s: nr_free is negative\n", __func__); +#endif + return; + } + + /* + * Slowpath, when this is the last pageblock of this region + * in this freelist. + */ + free_list->next_region->page_block = NULL; + + /* Set 'next_region' to the new first region in the freelist. */ + set_next_region_in_freelist(free_list); +} + +/* Generic delete function for region-aware buddy allocator. */ static void del_from_freelist(struct page *page, struct free_list *free_list) { struct list_head *prev_page_lru, *lru, *p; @@ -553,6 +603,11 @@ static void del_from_freelist(struct page *page, struct free_list *free_list) int region_id; lru = &page->lru; + + /* Try to fastpath, if deleting from the head of the list */ + if (lru == free_list->list.next) + return rmqueue_del_from_freelist(page, free_list); + region_id = page_zone_region_id(page); region = &free_list->mr_list[region_id]; region->nr_free--; @@ -588,6 +643,11 @@ page_found: prev_page_lru = lru->prev; list_del(lru); + /* + * Since we are not deleting from the head of the freelist, the + * 'next_region' pointer doesn't have to change. + */ + if (region->nr_free == 0) { region->page_block = NULL; } else { @@ -1013,7 +1073,7 @@ struct page *__rmqueue_smallest(struct zone *zone, unsigned int order, page = list_entry(area->free_list[migratetype].list.next, struct page, lru); - del_from_freelist(page, &area->free_list[migratetype]); + rmqueue_del_from_freelist(page, &area->free_list[migratetype]); rmv_page_order(page); area->nr_free--; expand(zone, page, order, current_order, area, migratetype); -- 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/