On Thu, Mar 16, 2017 at 10:17:18AM +0100, Michal Hocko wrote:
>[CC Mel]
>
>On Fri 10-03-17 14:41:22, Andrew Morton wrote:
>> From: Wei Yang <richard.weiyang@xxxxxxxxx>
>> Subject: mm/sparse: refine usemap_size() a little
>>
>> Current implementation calculates usemap_size in two steps:
>> * calculate number of bytes to cover these bits
>> * calculate number of "unsigned long" to cover these bytes
>>
>> It would be more clear by:
>> * calculate number of "unsigned long" to cover these bits
>> * multiple it with sizeof(unsigned long)
>>
>> This patch refine usemap_size() a little to make it more easy to
>> understand.
>
>I haven't checked deeply yet but reading through 5c0e3066474b ("Fix
>corruption of memmap on IA64 SPARSEMEM when mem_section is not a power
>of 2") made me ask whether the case described in the commit message
>still applies after this change or whether it has been considered at
>all.
>
Hi, Michal
Thanks for your comment.
By looking into the commit 5c0e3066474b, I think it does two things:
1. Recalculate the SECTION_BLOCKFLAGS_BITS
2. Move pageblock_flags out mem_section to make the structure power of 2 in
size.
When we look at the original data structure, pageblock_flags originally is
defined as a bitmap:
DECLARE_BITMAP(pageblock_flags, SECTION_BLOCKFLAGS_BITS);
Which in turn is:
#define DECLARE_BITMAP(pageblock_flags,SECTION_BLOCKFLAGS_BITS) \
unsigned long pageblock_flags[BITS_TO_LONGS(SECTION_BLOCKFLAGS_BITS)]
My patch is using BITS_TO_LONGS() to simplify the code and obviously has the
same effect.
Does this resolve your concern?
--
Wei Yang
Help you, Help me
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