linux-kernel - Re: [PATCH v4 1/9] slab: add opt-in caching layer of percpu sheaves

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Message-ID: <142aeeb5-d6d8-84ca-e7a2-ba564185c565@gentwo.org>
Date: Fri, 25 Apr 2025 10:31:45 -0700 (PDT)
From: "Christoph Lameter (Ampere)" <cl@...two.org>
To: Vlastimil Babka <vbabka@...e.cz>
cc: Suren Baghdasaryan <surenb@...gle.com>, 
    "Liam R. Howlett" <Liam.Howlett@...cle.com>, 
    David Rientjes <rientjes@...gle.com>, 
    Roman Gushchin <roman.gushchin@...ux.dev>, 
    Harry Yoo <harry.yoo@...cle.com>, Uladzislau Rezki <urezki@...il.com>, 
    linux-mm@...ck.org, linux-kernel@...r.kernel.org, rcu@...r.kernel.org, 
    maple-tree@...ts.infradead.org
Subject: Re: [PATCH v4 1/9] slab: add opt-in caching layer of percpu
 sheaves

On Fri, 25 Apr 2025, Vlastimil Babka wrote:

> @@ -4195,7 +4793,11 @@ static __fastpath_inline void *slab_alloc_node(struct kmem_cache *s, struct list
>  	if (unlikely(object))
>  		goto out;
>
> -	object = __slab_alloc_node(s, gfpflags, node, addr, orig_size);
> +	if (s->cpu_sheaves && node == NUMA_NO_NODE)
> +		object = alloc_from_pcs(s, gfpflags);

The node to use is determined in __slab_alloc_node() only based on the
memory policy etc. NUMA_NO_NODE allocations can be redirected by memory
policies and this check disables it.


> @@ -4653,7 +5483,10 @@ void slab_free(struct kmem_cache *s, struct slab *slab, void *object,
>  	memcg_slab_free_hook(s, slab, &object, 1);
>  	alloc_tagging_slab_free_hook(s, slab, &object, 1);
>
> -	if (likely(slab_free_hook(s, object, slab_want_init_on_free(s), false)))
> +	if (unlikely(!slab_free_hook(s, object, slab_want_init_on_free(s), false)))
> +		return;
> +
> +	if (!s->cpu_sheaves || !free_to_pcs(s, object))
>  		do_slab_free(s, slab, object, object, 1, addr);
>  }

We free to pcs even if the object is remote?