On Tue 26-06-12 16:24:39, Gavin Shan wrote: > >> >> >> 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 :-) > >> > >> >> > > >> >> >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@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>