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 <richard.weiyang@linux.alibaba.com>
Signed-off-by: Andrew 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: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/include/linux/pageblock-flags.h b/include/linux/pageblock-flags.h
index c066fec5b74bf1b48c26977a8e1ddd3a12dea9f8..6556e44744090d59a83877e37e034f97cd06e8cc 100644 (file)
--- 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 6c524fb76b317aeeb98ad9f72573a50d1c693f20..e1fdca9ef4e9676a89375ac1f3da6df444e548df 100644 (file)
--- 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