Hi Ankita, [ I don't really know anything about memory power management but here's my two cents since you asked for it. ] On Wed, Jun 29, 2011 at 4:00 PM, Ankita Garg <ankita@xxxxxxxxxx> wrote: > I) Dynamic Power Transition > > The goal here is to ensure that as much as possible, on an idle system, > the memory references do not get spread across the entire RAM, a problem > similar to memory fragmentation. The proposed approach is as below: > > 1) One of the first things is to ensure that the memory allocations do > not spill over to more number of regions. Thus the allocator needs to > be aware of the address boundary of the different regions. Why does the allocator need to know about address boundaries? Why isn't it enough to make the page allocator and reclaim policies favor using memory from lower addresses as aggressively as possible? That'd mean we'd favor the first memory banks and could keep the remaining ones powered off as much as possible. IOW, why do we need to support scenarios such as this: bank 0 bank 1 bank 2 bank3 | online | offline | online | offline | instead of using memory compaction and possibly something like the SLUB defragmentation patches to turn the memory map into this: bank 0 bank 1 bank 2 bank3 | online | online | offline | offline | > 2) At the time of allocation, before spilling over allocations to the > next logical region, the allocator needs to make a best attempt to > reclaim some memory from within the existing region itself first. The > reclaim here needs to be in LRU order within the region. However, if > it is ascertained that the reclaim would take a lot of time, like there > are quite a fe write-backs needed, then we can spill over to the next > memory region (just like our NUMA node allocation policy now). I think a much more important question is what happens _after_ we've allocated and free'd tons of memory few times. AFAICT, memory regions don't help with that kind of fragmentation that will eventually happen anyway. Pekka _______________________________________________ linux-pm mailing list linux-pm@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linux-foundation.org/mailman/listinfo/linux-pm
