Hi Dave, On Tue, May 31, 2011 at 10:34:20AM -0700, Dave Hansen wrote: > On Sun, 2011-05-29 at 13:46 +0530, Ankita Garg wrote: > > > It's worth noting that we already do targeted reclaim on boundaries > > > other than zones. The lumpy reclaim and memory compaction logically do > > > the same thing. So, it's at least possible to do this without having > > > the global LRU designed around the way you want to reclaim. > > > > > My understanding maybe incorrect, but doesn't both lumpy reclaim and > > memory compaction still work under zone boundary ? While trying to free > > up higher order pages, lumpy reclaim checks to ensure that pages that > > are selected do not cross zone boundary. Further, compaction walks > > through the pages in a zone and tries to re-arrange them. > > I'm asserting that we don't need memory regions in the > > pgdat->regions[]->zones[] > > layout to do what you're asking for. > > Lumpy reclaim is limited to a zone because it's trying to satisfy and > allocation request that came in for *THAT* *ZONE*. It's useless to go > clear out other zones. In your case, you don't care about zone > boundaries: you want to reclaim things regardless. > Ok true. So I guess lumpy reclaim could be extended to just free up pages spanning the entire region and not just a particular zone. > There was a "cma: Contiguous Memory Allocator added" patch posted a bit > ago to linux-mm@. You might want to take a look at it for some > inspiration. > We did take a look at CMA, but the use case seems to be slightly different. Inorder to allocate large contiguous pages, CMA creates a new miratetype called MIGRATE_CMA, which effectively isolates pages from the buddy allocator. > I think you also need to clearly establish here why any memory that > you're going to want to power off can't use (or shouldn't use) > ZONE_MOVABLE. It seems a bit silly to have it there, and ignore it for > such a similar use case. Memory hot-remove and power-down are not > horrifically different beasts. > Memory hot add and remove are definite usecases for conserving memory power. In this first version of the RFC patch, I have not yet added the support for ZONE_MOVABLE. I am currently testing the patch that creates movable zones under regions, thus ensuring that it can be easily evacuated using page migration. > BTW, that's probably something else to add to your list: make sure > mem_map[]s for memory in a region get allocated *in* that region. > There are a few reasons why we decided that we must have all the kernel non-movable data structures co-located in a single region as much as possible: - Having a region devoid of non-movable memory will enable the complete memory region to be even hot-removed - If the memory is evacuated and later turned off (loss of content), then the mem_map[]s will be lost. So when the memory comes back on, the mem_map[]s will need to be reinitialized. While the hotplug approach will work for exploiting PASR, it may not be the most efficient one - When the memory is put into a lower power state, having the mem_maps[]s in a single region would ensure that any references to just the struct pages will not lead to references to the actual memory However, it might be worth taking a look at it again. -- Regards, Ankita Garg (ankita@xxxxxxxxxx) Linux Technology Center IBM India Systems & Technology Labs, Bangalore, India -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxxx For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>