linux-kernel - Re: [PATCH v5 1/5] mm: introduce debug_pagealloc_{map,unmap}

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Date:   Mon, 9 Nov 2020 12:33:46 +0100
From:   Vlastimil Babka <vbabka@...e.cz>
To:     Mike Rapoport <rppt@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>
Cc:     Albert Ou <aou@...s.berkeley.edu>,
        Andy Lutomirski <luto@...nel.org>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Borislav Petkov <bp@...en8.de>,
        Catalin Marinas <catalin.marinas@....com>,
        Christian Borntraeger <borntraeger@...ibm.com>,
        Christoph Lameter <cl@...ux.com>,
        "David S. Miller" <davem@...emloft.net>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        David Hildenbrand <david@...hat.com>,
        David Rientjes <rientjes@...gle.com>,
        "Edgecombe, Rick P" <rick.p.edgecombe@...el.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        Heiko Carstens <hca@...ux.ibm.com>,
        Ingo Molnar <mingo@...hat.com>,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
        "Kirill A. Shutemov" <kirill@...temov.name>,
        Len Brown <len.brown@...el.com>,
        Michael Ellerman <mpe@...erman.id.au>,
        Mike Rapoport <rppt@...ux.ibm.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Paul Mackerras <paulus@...ba.org>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Pavel Machek <pavel@....cz>, Pekka Enberg <penberg@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Thomas Gleixner <tglx@...utronix.de>,
        Vasily Gorbik <gor@...ux.ibm.com>,
        Will Deacon <will@...nel.org>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, linux-pm@...r.kernel.org,
        linux-riscv@...ts.infradead.org, linux-s390@...r.kernel.org,
        linuxppc-dev@...ts.ozlabs.org, sparclinux@...r.kernel.org,
        x86@...nel.org
Subject: Re: [PATCH v5 1/5] mm: introduce debug_pagealloc_{map,unmap}_pages()
 helpers

On 11/8/20 7:57 AM, Mike Rapoport wrote:
> --- a/mm/slab.c
> +++ b/mm/slab.c
> @@ -1428,21 +1428,19 @@ static bool is_debug_pagealloc_cache(struct kmem_cache *cachep)
>   	return false;
>   }
>   
> -#ifdef CONFIG_DEBUG_PAGEALLOC
>   static void slab_kernel_map(struct kmem_cache *cachep, void *objp, int map)
>   {
>   	if (!is_debug_pagealloc_cache(cachep))
>   		return;

Hmm, I didn't notice earlier, sorry.
The is_debug_pagealloc_cache() above includes a debug_pagealloc_enabled_static() 
check, so it should be fine to use
__kernel_map_pages() directly below. Otherwise we generate two static key checks 
for the same key needlessly.

>   
> -	kernel_map_pages(virt_to_page(objp), cachep->size / PAGE_SIZE, map);
> +	if (map)
> +		debug_pagealloc_map_pages(virt_to_page(objp),
> +					  cachep->size / PAGE_SIZE);
> +	else
> +		debug_pagealloc_unmap_pages(virt_to_page(objp),
> +					    cachep->size / PAGE_SIZE);
>   }
>   
> -#else
> -static inline void slab_kernel_map(struct kmem_cache *cachep, void *objp,
> -				int map) {}
> -
> -#endif
> -
>   static void poison_obj(struct kmem_cache *cachep, void *addr, unsigned char val)
>   {
>   	int size = cachep->object_size;
> @@ -2062,7 +2060,7 @@ int __kmem_cache_create(struct kmem_cache *cachep, slab_flags_t flags)
>   
>   #if DEBUG
>   	/*
> -	 * If we're going to use the generic kernel_map_pages()
> +	 * If we're going to use the generic debug_pagealloc_map_pages()
>   	 * poisoning, then it's going to smash the contents of
>   	 * the redzone and userword anyhow, so switch them off.
>   	 */
>