Re: [PATCH v2 2/6] slub: Use alloc_pages_node() in alloc_slab_page()

["Christoph Lameter (Ampere)" <cl@gentwo.org>]

On Wed, 10 Jul 2024, Vlastimil Babka wrote:

>> With this patch cgroup restrictions memory policies etc etc no longer work
>> in the slab allocator.
>
> The only difference is memory policy from get_task_policy(), and the rest is
> the same, right?

There are also the cpuset/cgroup restrictions via the zonelists that are 
bypassed by removing alloc_pages()

> But this only affects new slab page allocation, while getting objects from
> existing slabs isn't subject to memory policies, so now it's at least
> consistent? Do you have some use case where it matters?

Yes this means you cannot redirect kmalloc based kernel metadata 
allocation when creating f.e. cgroups for another NUMA node. This affects 
all kernel metadata allocation during syscalls that used to be 
controllable via numa methods.

SLAB implemented memory allocations policies per object. SLUB moved that 
to implement these policies only when allocating a page frame. If this 
patch is left in then there wont be any support for memory allocation 
policies left in the slab allocators.

We have some internal patches now that implement memory policies on a per 
object basis for SLUB here.

This is a 10-15% regression on various benchmarks when objects like the 
scheduler statistics structures are misplaced.