On Tue, Feb 22, 2011 at 09:47:26AM -0600, Christoph Lameter wrote: > On Mon, 21 Feb 2011, Andi Kleen wrote: > > > Add a alloc_page_vma_node that allows passing the "local" node in. > > Use it in ksm to allocate copy pages on the same node as > > the original as possible. > > Why would that be useful? The shared page could be on a node that is not > near the process that maps the page. Would it not be better to allocate on > the node that is local to the process that maps the page? This is what I was trying to understand. To me it looks like this is making things worse. Following the "vma" advice like current code does, sounds much better than following the previous page that may have been allocated in the wrong node if the allocation from the right node couldn't be satisfied at the time the page was first allocated (we should still try to allocate from the right node following the vma hint). In the KSM case this badness is exacerbated by the fact a ksm page is guarnteed to be randomly-numa allocated, because it's shared across all processes regardless of their vma settings. KSM is not NUMA aware, so following the location of the KSM "page" seems a regression compared to the current code that at least follows the vma when bringing up a page during swapin. I've an hard time generally to see how following "page" (that is especially wrong with KSM because of the very sharing effect) is better than following "vma". KSM may become NUMA aware if we replicate the stable tree in each node, but we're not even close to that, so I've an hard time how "page" hinting instead of "vma" hinting can do any good, especially in KSM case. But I've to think more about this.. but if you've suggestions you're welcome. -- 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>