From: Wei Yang <richard.weiyang@xxxxxxxxxxxxxxxxx>
Subject: 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.
Link: http://lkml.kernel.org/r/20200623124201.8199-3-richard.weiyang@xxxxxxxxxxxxxxxxx
Signed-off-by: Wei Yang <richard.weiyang@xxxxxxxxxxxxxxxxx>
Cc: Mel Gorman <mgorman@xxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
include/linux/pageblock-flags.h | 22 +++++++---------------
mm/page_alloc.c | 13 ++++++-------
2 files changed, 13 insertions(+), 22 deletions(-)
--- a/include/linux/pageblock-flags.h~mm-page_allocc-simplify-pageblock-bitmap-access
+++ a/include/linux/pageblock-flags.h
@@ -66,25 +66,17 @@ void set_pfnblock_flags_mask(struct 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)
{
--- a/mm/page_alloc.c~mm-page_allocc-simplify-pageblock-bitmap-access
+++ a/mm/page_alloc.c
@@ -489,8 +489,7 @@ static __always_inline unsigned long __g
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
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 pa
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
_
