linux-kernel - Re: [RFC PATCH 05/14] mm/slub: create folio_set/clear

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Date:   Fri, 15 Sep 2023 14:02:13 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Matteo Rizzo <matteorizzo@...gle.com>
Cc:     cl@...ux.com, penberg@...nel.org, rientjes@...gle.com,
        iamjoonsoo.kim@....com, akpm@...ux-foundation.org, vbabka@...e.cz,
        roman.gushchin@...ux.dev, 42.hyeyoo@...il.com,
        linux-kernel@...r.kernel.org, linux-doc@...r.kernel.org,
        linux-mm@...ck.org, linux-hardening@...r.kernel.org,
        tglx@...utronix.de, mingo@...hat.com, bp@...en8.de,
        dave.hansen@...ux.intel.com, x86@...nel.org, hpa@...or.com,
        corbet@....net, luto@...nel.org, peterz@...radead.org,
        jannh@...gle.com, evn@...gle.com, poprdi@...gle.com,
        jordyzomer@...gle.com
Subject: Re: [RFC PATCH 05/14] mm/slub: create folio_set/clear_slab helpers

On Fri, Sep 15, 2023 at 10:59:24AM +0000, Matteo Rizzo wrote:
> From: Jann Horn <jannh@...gle.com>
> 
> This is refactoring in preparation for SLAB_VIRTUAL. Extract this code
> to separate functions so that it's not duplicated in the code that
> allocates and frees page with SLAB_VIRTUAL enabled.
> 
> Signed-off-by: Jann Horn <jannh@...gle.com>
> Co-developed-by: Matteo Rizzo <matteorizzo@...gle.com>
> Signed-off-by: Matteo Rizzo <matteorizzo@...gle.com>
> ---
>  mm/slub.c | 32 ++++++++++++++++++++++----------
>  1 file changed, 22 insertions(+), 10 deletions(-)
> 
> diff --git a/mm/slub.c b/mm/slub.c
> index ad33d9e1601d..9b87afade125 100644
> --- a/mm/slub.c
> +++ b/mm/slub.c
> @@ -1849,6 +1849,26 @@ static void *setup_object(struct kmem_cache *s, void *object)
>  /*
>   * Slab allocation and freeing
>   */
> +
> +static void folio_set_slab(struct folio *folio, struct slab *slab)
> +{
> +	__folio_set_slab(folio);
> +	/* Make the flag visible before any changes to folio->mapping */
> +	smp_wmb();
> +
> +	if (folio_is_pfmemalloc(folio))
> +		slab_set_pfmemalloc(slab);
> +}
> +
> +static void folio_clear_slab(struct folio *folio, struct slab *slab)
> +{
> +	__slab_clear_pfmemalloc(slab);
> +	folio->mapping = NULL;
> +	/* Make the mapping reset visible before clearing the flag */
> +	smp_wmb();
> +	__folio_clear_slab(folio);
> +}

Perhaps these should be explicitly marked as inlines?

> +
>  static inline struct slab *alloc_slab_page(gfp_t flags, int node,
>  		struct kmem_cache_order_objects oo)
>  {
> @@ -1865,11 +1885,7 @@ static inline struct slab *alloc_slab_page(gfp_t flags, int node,
>  		return NULL;
>  
>  	slab = folio_slab(folio);
> -	__folio_set_slab(folio);
> -	/* Make the flag visible before any changes to folio->mapping */
> -	smp_wmb();
> -	if (folio_is_pfmemalloc(folio))
> -		slab_set_pfmemalloc(slab);
> +	folio_set_slab(folio, slab);
>  
>  	return slab;
>  }
> @@ -2067,11 +2083,7 @@ static void __free_slab(struct kmem_cache *s, struct slab *slab)
>  	int order = folio_order(folio);
>  	int pages = 1 << order;
>  
> -	__slab_clear_pfmemalloc(slab);
> -	folio->mapping = NULL;
> -	/* Make the mapping reset visible before clearing the flag */
> -	smp_wmb();
> -	__folio_clear_slab(folio);
> +	folio_clear_slab(folio, slab);
>  	mm_account_reclaimed_pages(pages);
>  	unaccount_slab(slab, order, s);
>  	__free_pages(&folio->page, order);
> -- 
> 2.42.0.459.ge4e396fd5e-goog

Otherwise this is a straight function extraction.

Reviewed-by: Kees Cook <keescook@...omium.org>

-- 
Kees Cook