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 <[email protected]> >> 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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