On Mon, Nov 28, 2016 at 09:39:19AM -0600, Christoph Lameter wrote: > On Sun, 27 Nov 2016, Mel Gorman wrote: > > > > > SLUB has been the default small kernel object allocator for quite some time > > but it is not universally used due to performance concerns and a reliance > > on high-order pages. The high-order concerns has two major components -- > > high-order pages are not always available and high-order page allocations > > potentially contend on the zone->lock. This patch addresses some concerns > > about the zone lock contention by extending the per-cpu page allocator to > > cache high-order pages. The patch makes the following modifications > > Note that SLUB will only use high order pages when available and fall back > to order 0 if memory is fragmented. This means that the effect of this > patch is going to gradually vanish as memory becomes more and more > fragmented. > Yes, that's a problem for SLUB with or without this patch. It's always been the case that SLUB relying on high-order pages for performance is problematic. > I think this patch is beneficial but we need to address long term the > issue of memory fragmentation. That is not only a SLUB issue but an > overall problem since we keep on having to maintain lists of 4k memory > blocks in variuos subsystems. And as memory increases these lists are > becoming larger and larger and more difficult to manage. Code complexity > increases and fragility too (look at transparent hugepages). Ultimately we > will need a clean way to manage the allocation and freeing of large > physically contiguous pages. Reserving memory at booting (CMA, giant > pages) is some sort of solution but this all devolves into lots of knobs > that only insiders know how to tune and an overall fragile solution. > While I agree with all of this, it's also a problem independent of this patch. -- Mel Gorman SUSE Labs -- 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>