On Wed, Jul 11, 2018 at 2:21 AM Michal Hocko <mho...@kernel.org> wrote: > > We already have an interface for that. alloc_pages(GFP_NOWAIT, MAX_ORDER -1). > So why do we need any array based interface?
That was actually my original argument in the original thread - that the only new interface people might want is one that just tells how many of those MAX_ORDER-1 pages there are. See the thread in v33 with the subject "[PATCH v33 1/4] mm: add a function to get free page blocks" and look for me suggesting just using #define GFP_MINFLAGS (__GFP_NORETRY | __GFP_NOWARN | __GFP_THISNODE | __GFP_NOMEMALLOC) struct page *page = alloc_pages(GFP_MINFLAGS, MAX_ORDER-1); for this all. But I could also see an argument for "allocate N pages of size MAX_ORDER-1", with some small N, simply because I can see the advantage of not taking and releasing the locking and looking up the zone individually N times. If you want to get gigabytes of memory (or terabytes), doing it in bigger chunks than one single maximum-sized page sounds fairly reasonable. I just don't think that "thousands of pages" is reasonable. But "tens of max-sized pages" sounds fair enough to me, and it would certainly not be a pain for the VM. So I'm open to new interfaces. I just want those new interfaces to make sense, and be low latency and simple for the VM to do. I'm objecting to the incredibly baroque and heavy-weight one that can return near-infinite amounts of memory. The real advantage of jjuist the existing "alloc_pages()" model is that I think the ballooning people can use that to *test* things out. If it turns out that taking and releasing the VM locks is a big cost, we can see if a batch interface that allows you to get tens of pages at the same time is worth it. So yes, I'd suggest starting with just the existing alloc_pages. Maybe it's not enough, but it should be good enough for testing. Linus _______________________________________________ Virtualization mailing list Virtualization@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/virtualization