Commit d93d5ab9 authored by Wei Yang's avatar Wei Yang Committed by Linus Torvalds
Browse files

mm/page_alloc.c: simplify pageblock bitmap access 



Due to commit e58469ba ("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: default avatarWei Yang <richard.weiyang@linux.alibaba.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Cc: Mel Gorman <mgorman@suse.de>
Link: http://lkml.kernel.org/r/20200623124201.8199-3-richard.weiyang@linux.alibaba.com


Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 399b795b

include/linux/pageblock-flags.h

+7 −15
Original line number Diff line number Diff line
@@ -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)

{

mm/page_alloc.c

+6 −7
Original line number Diff line number Diff line
@@ -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

CRA Git | Maintained and supported by SUSTech CRA and CCSE