Re: [PATCH v2] mm/slub: allocate sheaves on local memory nodes

[Harry Yoo <harry@kernel.org>]

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On 6/1/26 6:56 PM, Hao Li wrote:
> Sheaf structs are exchanged through node-local barns. Since barn structs
> are already allocated from their local NUMA node, this patch aims to
> allocate sheaf structs from their local memory nodes as well.
> 
> To achieve this, the obvious choice would be using cpu_to_mem().
> However, init_percpu_sheaves() and bootstrap_cache_sheaves() iterate
> through possible CPUs, whereas cpu_to_mem() is only initialized for
> online CPUs. Therefore, we cannot use cpu_to_mem() and instead need to
> use local_memory_node(cpu_to_node(cpu)), similar to what
> __build_all_zonelists() does.
> 
> The primary goal of this patch is to improve NUMA node locality.
> Although the actual performance impact is minor, it still yields a ~1%
> improvement on a 192-core, 8-NUMA-node system when testing with the
> will-it-scale mmap test case.

Oh, nice :)

I have a question though...

I wonder if would be better to handle this by e.g.) not returning empty
sheaves back to barn and freeing them if the node id doesn't match and
it's not a memoryless node.

init_percpu_sheaves() and bootstrap_cache_sheaves() are not the only
places that can allocate sheaves from remote nodes; sheaves allocation
could fall back to other nodes and then SLUB could keep reusing those
sheaves from remote nodes even after memory is reclaimed.

If this works well, we probably don't need to handle it in
init_percpu_sheaves() and bootstrap_cache_sheaves() at all as they will
eventually be freed, while covering the other case too?

> Signed-off-by: Hao Li <hao.li@linux.dev>
> ---
> Changes in v2:
> - Make init_percpu_sheaves() use a NUMA-aware sheaf struct allocation too.
>   (Thanks Harry)
> - Rebase on latest code.
> 
> v1: https://lore.kernel.org/linux-mm/20260525082312.16012-1-hao.li@linux.dev/


-- 
Cheers,
Harry / Hyeonggon


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