On Wed, Jul 16, 2014 at 01:14:26PM +0200, Vlastimil Babka wrote: > On 07/16/2014 10:43 AM, Joonsoo Kim wrote: > >> I think your plan of multiple parallel CMA allocations (and thus > >> multiple parallel isolations) is also possible. The isolate pcplists > >> can be shared by pages coming from multiple parallel isolations. But > >> the flush operation needs a pfn start/end parameters to only flush > >> pages belonging to the given isolation. That might mean a bit of > >> inefficient list traversing, but I don't think it's a problem. > > > > I think that special pcplist would cause a problem if we should check > > pfn range. If there are too many pages on this pcplist, move pages from > > this pcplist to isolate freelist takes too long time in irq context and > > system could be broken. This operation cannot be easily stopped because > > it is initiated by IPI on other cpu and starter of this IPI expect that > > all pages on other cpus' pcplist are moved properly when returning > > from on_each_cpu(). > > > > And, if there are so many pages, serious lock contention would happen > > in this case. > > Hm I see. So what if it wasn't a special pcplist, but a special "free list" > where the pages would be just linked together as on pcplist, regardless of > order, and would not merge until the CPU that drives the memory isolation > process decides it is safe to flush them away. That would remove the need for > IPI's and provide the same guarantees I think. Looks good. It would work. I think that your solution is better than mine. I will implement it and test. > > > Anyway, my idea's key point is using PageIsolated() to distinguish > > isolated page, instead of using PageBuddy(). If page is PageIsolated(), > > Is PageIsolated a completely new page flag? Those are a limited resource so I > would expect some resistance to such approach. Or a new special page->_mapcount > value? That could maybe work. Yes, it is new special page->_mapcount. > > it isn't handled as freepage although it is in buddy allocator. During free, > > page with MIGRATETYPE_ISOLATE will be marked as PageIsolated() and > > won't be merged and counted for freepage. > > OK. Preventing wrong merging is the key point and this should work. > > > When we move pages from normal buddy list to isolate buddy > > list, we check PageBuddy() and subtract number of PageBuddy() pages > > Do we really need to check PageBuddy()? Could a page get marked as PageIsolate() > but still go to normal list instead of isolate list? Checking PageBuddy() is used for identifying page linked in normal list. Thanks. -- 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>