From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-ee0-f51.google.com (mail-ee0-f51.google.com [74.125.83.51]) by kanga.kvack.org (Postfix) with ESMTP id 8377B6B004D for ; Fri, 18 Apr 2014 10:50:50 -0400 (EDT) Received: by mail-ee0-f51.google.com with SMTP id c13so1700787eek.38 for ; Fri, 18 Apr 2014 07:50:50 -0700 (PDT) Received: from mx2.suse.de (cantor2.suse.de. [195.135.220.15]) by mx.google.com with ESMTPS id z2si40615447eeo.34.2014.04.18.07.50.48 for (version=TLSv1 cipher=ECDHE-RSA-RC4-SHA bits=128/128); Fri, 18 Apr 2014 07:50:49 -0700 (PDT) From: Mel Gorman Subject: [PATCH 10/16] mm: page_alloc: Use word-based accesses for get/set pageblock bitmaps Date: Fri, 18 Apr 2014 15:50:37 +0100 Message-Id: <1397832643-14275-11-git-send-email-mgorman@suse.de> In-Reply-To: <1397832643-14275-1-git-send-email-mgorman@suse.de> References: <1397832643-14275-1-git-send-email-mgorman@suse.de> Sender: owner-linux-mm@kvack.org List-ID: To: Linux-MM Cc: Linux-FSDevel The test_bit operations in get/set pageblock flags are expensive. This patch reads the bitmap on a word basis and use shifts and masks to isolate the bits of interest. Similarly masks are used to set a local copy of the bitmap and then use cmpxchg to update the bitmap if there have been no other changes made in parallel. In a test running dd onto tmpfs the overhead of the pageblock-related functions went from 1.27% in profiles to 0.5%. Signed-off-by: Mel Gorman --- include/linux/mmzone.h | 6 +++++- include/linux/pageblock-flags.h | 21 ++++++++++++++++---- mm/page_alloc.c | 43 +++++++++++++++++++++++++---------------- 3 files changed, 48 insertions(+), 22 deletions(-) diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h index c1dbe0b..c97b4bc 100644 --- a/include/linux/mmzone.h +++ b/include/linux/mmzone.h @@ -75,9 +75,13 @@ enum { extern int page_group_by_mobility_disabled; +#define NR_MIGRATETYPE_BITS 3 +#define MIGRATETYPE_MASK ((1UL << NR_MIGRATETYPE_BITS) - 1) + static inline int get_pageblock_migratetype(struct page *page) { - return get_pageblock_flags_group(page, PB_migrate, PB_migrate_end); + BUILD_BUG_ON(PB_migrate_end - PB_migrate != 2); + return get_pageblock_flags_mask(page, NR_MIGRATETYPE_BITS, MIGRATETYPE_MASK); } struct free_area { diff --git a/include/linux/pageblock-flags.h b/include/linux/pageblock-flags.h index 2ee8cd2..c89ac75 100644 --- a/include/linux/pageblock-flags.h +++ b/include/linux/pageblock-flags.h @@ -30,9 +30,12 @@ enum pageblock_bits { PB_migrate, PB_migrate_end = PB_migrate + 3 - 1, /* 3 bits required for migrate types */ -#ifdef CONFIG_COMPACTION PB_migrate_skip,/* If set the block is skipped by compaction */ -#endif /* CONFIG_COMPACTION */ + + /* + * Assume the bits will always align on a word. If this assumption + * changes then get/set pageblock needs updating. + */ NR_PAGEBLOCK_BITS }; @@ -62,9 +65,19 @@ extern int pageblock_order; /* Forward declaration */ struct page; +unsigned long get_pageblock_flags_mask(struct page *page, + unsigned long nr_flag_bits, + unsigned long mask); + /* Declarations for getting and setting flags. See mm/page_alloc.c */ -unsigned long get_pageblock_flags_group(struct page *page, - int start_bitidx, int end_bitidx); +static inline unsigned long get_pageblock_flags_group(struct page *page, + int start_bitidx, int end_bitidx) +{ + unsigned long nr_flag_bits = end_bitidx - start_bitidx + 1; + unsigned long mask = (1 << nr_flag_bits) - 1; + + return get_pageblock_flags_mask(page, nr_flag_bits, mask); +} void set_pageblock_flags_group(struct page *page, unsigned long flags, int start_bitidx, int end_bitidx); diff --git a/mm/page_alloc.c b/mm/page_alloc.c index 737577c..6047866 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -6012,25 +6012,24 @@ static inline int pfn_to_bitidx(struct zone *zone, unsigned long pfn) * @end_bitidx: The last bit of interest * returns pageblock_bits flags */ -unsigned long get_pageblock_flags_group(struct page *page, - int start_bitidx, int end_bitidx) +unsigned long get_pageblock_flags_mask(struct page *page, + unsigned long nr_flag_bits, + unsigned long mask) { struct zone *zone; unsigned long *bitmap; - unsigned long pfn, bitidx; - unsigned long flags = 0; - unsigned long value = 1; + unsigned long pfn, bitidx, word_bitidx; + unsigned long word; zone = page_zone(page); pfn = page_to_pfn(page); bitmap = get_pageblock_bitmap(zone, pfn); bitidx = pfn_to_bitidx(zone, pfn); + word_bitidx = bitidx / BITS_PER_LONG; + bitidx &= (BITS_PER_LONG-1); - for (; start_bitidx <= end_bitidx; start_bitidx++, value <<= 1) - if (test_bit(bitidx + start_bitidx, bitmap)) - flags |= value; - - return flags; + word = bitmap[word_bitidx]; + return (word >> (BITS_PER_LONG - (bitidx + nr_flag_bits))) & mask; } /** @@ -6045,20 +6044,30 @@ void set_pageblock_flags_group(struct page *page, unsigned long flags, { struct zone *zone; unsigned long *bitmap; - unsigned long pfn, bitidx; - unsigned long value = 1; + unsigned long pfn, bitidx, word_bitidx; + unsigned long nr_flag_bits = end_bitidx - start_bitidx + 1; + unsigned long mask = (1 << nr_flag_bits) - 1; + unsigned long old_word, new_word; + + BUILD_BUG_ON(NR_PAGEBLOCK_BITS != 4); zone = page_zone(page); pfn = page_to_pfn(page); bitmap = get_pageblock_bitmap(zone, pfn); bitidx = pfn_to_bitidx(zone, pfn); + word_bitidx = bitidx / BITS_PER_LONG; + bitidx &= (BITS_PER_LONG-1); + VM_BUG_ON_PAGE(!zone_spans_pfn(zone, pfn), page); - for (; start_bitidx <= end_bitidx; start_bitidx++, value <<= 1) - if (flags & value) - __set_bit(bitidx + start_bitidx, bitmap); - else - __clear_bit(bitidx + start_bitidx, bitmap); + end_bitidx = bitidx + (end_bitidx - start_bitidx); + mask <<= (BITS_PER_LONG - end_bitidx - 1); + flags <<= (BITS_PER_LONG - end_bitidx - 1); + + do { + old_word = ACCESS_ONCE(bitmap[word_bitidx]); + new_word = (old_word & ~mask) | flags; + } while (cmpxchg(&bitmap[word_bitidx], old_word, new_word) != old_word); } /* -- 1.8.4.5 -- 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