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>
2 files changed
