linux-kernel - Re: [PATCH v5 01/14] slab: add opt-in caching layer of percpu sheaves

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Message-ID: <20250914022258.7062-1-hdanton@sina.com>
Date: Sun, 14 Sep 2025 10:22:57 +0800
From: Hillf Danton <hdanton@...a.com>
To: Vlastimil Babka <vbabka@...e.cz>
Cc: linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v5 01/14] slab: add opt-in caching layer of percpu sheaves

On Wed, 23 Jul 2025 15:34:34 +0200 Vlastimil Babka wrote:
> +
> +/*
> + * Caller needs to make sure migration is disabled in order to fully flush
> + * single cpu's sheaves
> + *
This misguides, see below for a workqueue case.

> + * must not be called from an irq
> + *
> + * flushing operations are rare so let's keep it simple and flush to slabs
> + * directly, skipping the barn
> + */
> +static void pcs_flush_all(struct kmem_cache *s)
> +{
> +	struct slub_percpu_sheaves *pcs;
> +	struct slab_sheaf *spare;
> +
> +	local_lock(&s->cpu_sheaves->lock);
> +	pcs = this_cpu_ptr(s->cpu_sheaves);
> +
> +	spare = pcs->spare;
> +	pcs->spare = NULL;
> +
> +	local_unlock(&s->cpu_sheaves->lock);
> +
> +	if (spare) {
> +		sheaf_flush_unused(s, spare);
> +		free_empty_sheaf(s, spare);
> +	}
> +
> +	sheaf_flush_main(s);
> +}
> +
> @@ -3326,30 +3755,18 @@ struct slub_flush_work {
>  static void flush_cpu_slab(struct work_struct *w)
>  {
>  	struct kmem_cache *s;
> -	struct kmem_cache_cpu *c;
>  	struct slub_flush_work *sfw;
>  
>  	sfw = container_of(w, struct slub_flush_work, work);
>  
>  	s = sfw->s;
> -	c = this_cpu_ptr(s->cpu_slab);
>  
> -	if (c->slab)
> -		flush_slab(s, c);
> +	if (s->cpu_sheaves)
> +		pcs_flush_all(s);
>  
Migration is not disabled.

> -	put_partials(s);
> +	flush_this_cpu_slab(s);
>  }