On Fri, Feb 16, 2018 at 09:44:25AM -0600, Christopher Lameter wrote: > On Thu, 15 Feb 2018, Matthew Wilcox wrote: > > What I was proposing was an intermediate page allocator where slab would > > request 2MB for its own uses all at once, then allocate pages from that to > > individual slabs, so allocating a kmalloc-32 object and a dentry object > > would result in 510 pages of memory still being available for any slab > > that needed it. > > Well thats not really going to work since you would be mixing objects of > different sizes which may present more fragmentation problems within the > 2M later if they are freed and more objects are allocated.
I don't understand this response. I'm not suggesting mixing objects of different sizes within the same page. The vast majority of slabs use order-0 pages, a few use order-1 pages and larger sizes are almost unheard of. I'm suggesting the slab have it's own private arena of pages that it uses for allocating pages to slabs; when an entire page comes free in a slab, it is returned to the arena. When the arena is empty, slab requests another arena from the page allocator. If you're concerned about order-0 allocations fragmenting the arena for order-1 slabs, then we could have separate arenas for order-0 and order-1. But there should be no more fragmentation caused by sticking within an arena for page allocations than there would be by spreading slab allocations across all memory.
