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Date:   Fri, 15 Sep 2023 14:02:13 -0700
From:   Kees Cook <keescook@chromium.org>
To:     Matteo Rizzo <matteorizzo@google.com>
Cc:     cl@linux.com, penberg@kernel.org, rientjes@google.com,
        iamjoonsoo.kim@lge.com, akpm@linux-foundation.org, vbabka@suse.cz,
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        linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org,
        linux-mm@kvack.org, linux-hardening@vger.kernel.org,
        tglx@linutronix.de, mingo@redhat.com, bp@alien8.de,
        dave.hansen@linux.intel.com, x86@kernel.org, hpa@zytor.com,
        corbet@lwn.net, luto@kernel.org, peterz@infradead.org,
        jannh@google.com, evn@google.com, poprdi@google.com,
        jordyzomer@google.com
Subject: Re: [RFC PATCH 05/14] mm/slub: create folio_set/clear_slab helpers
Message-ID: <202309151401.C49DDCE8@keescook>
References: <20230915105933.495735-1-matteorizzo@google.com>
 <20230915105933.495735-6-matteorizzo@google.com>
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On Fri, Sep 15, 2023 at 10:59:24AM +0000, Matteo Rizzo wrote:
> From: Jann Horn <jannh@google.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@google.com>
> Co-developed-by: Matteo Rizzo <matteorizzo@google.com>
> Signed-off-by: Matteo Rizzo <matteorizzo@google.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@chromium.org>

-- 
Kees Cook