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
