Re: [LSF/MM/BPF TOPIC] SLAB BOF

[David Hildenbrand <david@redhat.com>]

On 22.04.24 16:23, Matthew Wilcox wrote:
> I have a fairly radical idea for a new slab allocator design which
> I want to sit down with Vlastimil and a whiteboard to flesh out.
> Obviously the two of us could just sneak off somewhere, but it'd
> probably make more sense to schedule this as a BOF.
> 
> The basic idea is to decouple the objects from the page they reside in.
> Instead of having a struct slab to organise the objects on this page,
> we organise the objects into sheaves.  A sheaf always contains objects
> from the same NUMA node, but not necessarily the same page.  For each
> kmem_cache, there is a per-NUMA-node barn which the per-CPU front end of
> the slab allocator will request full sheaves from and give full sheaves
> back to.  If we RCU-free an object, that goes to the per-CPU rcu-freeing
> sheaf, which is handed to RCU once full.
> 
> The obvious objection to all of this is that the story for reclaiming
> pages from slab is pretty awful.  I'd hope to brainstorm some idea for
> improving that (perhaps in the construction of the barn where we could
> pull sheaves part and put them back together in some kind of order?)

Just as a side note, I would be interested into something that can 
easily reclaim pages from slab in a specific physical memory area. 
Target use cases are around alloc_contig_range(), memory offlining an 
similar.

... but IIUC, the barn/sheep approach wouldn't make that any easier, right?

-- 
Cheers,

David / dhildenb