On Tue 26-06-12 16:24:39, Gavin Shan wrote:

quoted

quoted

quoted

quoted

quoted

quoted

In order to fully utilize the memory chunk allocated from bootmem
allocator, it'd better to assure memory sector descriptor won't run
across the boundary (PAGE_SIZE).

OK, I misread this part of the changelog changelog.

I should have clarified that more clear :-)

quoted

quoted

quoted

Why? The memory is continuous, right?

Yes, the memory is conginous and the capacity of specific entry
in mem_section[NR_SECTION_ROOTS] has been defined as follows:


#define SECTIONS_PER_ROOT       (PAGE_SIZE / sizeof (struct mem_section))

Also, the memory is prone to be allocated from bootmem by function
alloc_bootmem_node(), which has PAGE_SIZE alignment. So I think it's
reasonable to introduce the extra check here from my personal view :-)

No it is not necessary because we will never cross the page boundary
because (SECTIONS_PER_ROOT uses an int division)

Current situation is that we don't cross the page foundary, but somebody
else might change the data struct (struct mem_section) in future. 

No, this is safe even if the structure size changes (unless it is bigger
than PAGE_SIZE).

Yeah, but it can't fully utilize the allocated memory chunk if the size of
the struct isn't aligned well.

And you think that this is justification is sufficient to fail
compilation? I don't think so...

Let me drop it in next revision :-)

Thanks,
Gavin

-- 
Michal Hocko
SUSE Labs
SUSE LINUX s.r.o.
Lihovarska 1060/12
190 00 Praha 9    
Czech Republic

--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@kvack.org.  For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>