On 02/21/2018 07:42 AM, Matthew Wilcox wrote: > On Tue, Jan 23, 2018 at 01:55:32PM +0300, Konstantin Khlebnikov wrote: >> Virtually mapped stack have two bonuses: it eats order-0 pages and >> adds guard page at the end. But it slightly slower if system have >> plenty free high-order pages. >> >> This patch adds option to use virtually bapped stack as fallback for >> atomic allocation of traditional high-order page. > This prompted me to write a patch I've been meaning to do for a while, > allocating large pages if they're available to satisfy vmalloc. I thought > it would save on touching multiple struct pages, but it turns out that > the checking code we currently have in the free_pages path requires you > to have initialised all of the tail pages (maybe we can make that code > conditional ...) What the concept here? If we can use high-order pages for vmalloc() at the moment, we *should* use them? One of the coolest things about vmalloc() is that it can do large allocations without consuming large (high-order) pages, so it has very few side-effects compared to doing a bunch of order-0 allocations. This patch seems to propose removing that cool thing. Even trying the high-order allocation could kick off a bunch of reclaim and compaction that was not there previously. If you could take this an only _opportunistically_ allocate large pages, it could be a more universal win. You could try to make sure that no compaction or reclaim is done for the large allocation. Or, maybe you only try it if there are *only* high-order pages in the allocator that would have been broken down into order-0 *anyway*. I'm not sure it's worth it, though. I don't see a lot of folks complaining about vmalloc()'s speed or TLB impact. -- 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>
