From d93d5ab9ca01e24efc6add60371b0d5684b5c146 Mon Sep 17 00:00:00 2001 From: Wei Yang Date: Thu, 6 Aug 2020 23:25:48 -0700 Subject: [PATCH] mm/page_alloc.c: simplify pageblock bitmap access Due to commit e58469bafd05 ("mm: page_alloc: use word-based accesses for get/set pageblock bitmaps"), pageblock bitmap is accessed with word-based access. This operation could be simplified a little. Intuitively, if we want to get a bit range [start_idx, end_idx] in a word, we can do like this: mask = (1 << (end_bitidx - start_bitidx + 1)) - 1; ret = (word >> start_idx) & mask; And also if we want to set a bit range [start_idx, end_idx] with flags, we can do the same by just shift start_bitidx. By doing so we reduce some instructions for these two helper functions: Before Patched set_pfnblock_flags_mask 209 198(-5%) get_pfnblock_flags_mask 101 87(-13%) Since the syntax is changed a little, we need to check the whole 4-bit migrate_type instead of part of it. Signed-off-by: Wei Yang Signed-off-by: Andrew Morton Cc: Mel Gorman Link: http://lkml.kernel.org/r/20200623124201.8199-3-richard.weiyang@linux.alibaba.com Signed-off-by: Linus Torvalds --- include/linux/pageblock-flags.h | 22 +++++++--------------- mm/page_alloc.c | 13 ++++++------- 2 files changed, 13 insertions(+), 22 deletions(-) diff --git a/include/linux/pageblock-flags.h b/include/linux/pageblock-flags.h index c066fec5b74b..6556e4474409 100644 --- a/include/linux/pageblock-flags.h +++ b/include/linux/pageblock-flags.h @@ -66,25 +66,17 @@ void set_pfnblock_flags_mask(struct page *page, unsigned long mask); /* Declarations for getting and setting flags. See mm/page_alloc.c */ -#define get_pageblock_flags_group(page, start_bitidx, end_bitidx) \ - get_pfnblock_flags_mask(page, page_to_pfn(page), \ - end_bitidx, \ - (1 << (end_bitidx - start_bitidx + 1)) - 1) -#define set_pageblock_flags_group(page, flags, start_bitidx, end_bitidx) \ - set_pfnblock_flags_mask(page, flags, page_to_pfn(page), \ - end_bitidx, \ - (1 << (end_bitidx - start_bitidx + 1)) - 1) - #ifdef CONFIG_COMPACTION #define get_pageblock_skip(page) \ - get_pageblock_flags_group(page, PB_migrate_skip, \ - PB_migrate_skip) + get_pfnblock_flags_mask(page, page_to_pfn(page), \ + PB_migrate_skip, (1 << (PB_migrate_skip))) #define clear_pageblock_skip(page) \ - set_pageblock_flags_group(page, 0, PB_migrate_skip, \ - PB_migrate_skip) + set_pfnblock_flags_mask(page, 0, page_to_pfn(page), \ + PB_migrate_skip, (1 << PB_migrate_skip)) #define set_pageblock_skip(page) \ - set_pageblock_flags_group(page, 1, PB_migrate_skip, \ - PB_migrate_skip) + set_pfnblock_flags_mask(page, (1 << PB_migrate_skip), \ + page_to_pfn(page), \ + PB_migrate_skip, (1 << PB_migrate_skip)) #else static inline bool get_pageblock_skip(struct page *page) { diff --git a/mm/page_alloc.c b/mm/page_alloc.c index 6c524fb76b31..e1fdca9ef4e9 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -489,8 +489,7 @@ static __always_inline unsigned long __get_pfnblock_flags_mask(struct page *page bitidx &= (BITS_PER_LONG-1); word = bitmap[word_bitidx]; - bitidx += end_bitidx; - return (word >> (BITS_PER_LONG - bitidx - 1)) & mask; + return (word >> bitidx) & mask; } unsigned long get_pfnblock_flags_mask(struct page *page, unsigned long pfn, @@ -532,9 +531,8 @@ void set_pfnblock_flags_mask(struct page *page, unsigned long flags, VM_BUG_ON_PAGE(!zone_spans_pfn(page_zone(page), pfn), page); - bitidx += end_bitidx; - mask <<= (BITS_PER_LONG - bitidx - 1); - flags <<= (BITS_PER_LONG - bitidx - 1); + mask <<= bitidx; + flags <<= bitidx; word = READ_ONCE(bitmap[word_bitidx]); for (;;) { @@ -551,8 +549,9 @@ void set_pageblock_migratetype(struct page *page, int migratetype) migratetype < MIGRATE_PCPTYPES)) migratetype = MIGRATE_UNMOVABLE; - set_pageblock_flags_group(page, (unsigned long)migratetype, - PB_migrate, PB_migrate_end); + set_pfnblock_flags_mask(page, (unsigned long)migratetype, + page_to_pfn(page), PB_migrate_end, + MIGRATETYPE_MASK); } #ifdef CONFIG_DEBUG_VM