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Date:   Fri, 29 Apr 2022 11:56:31 +0200
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Subject: Re: [PATCH v5 2/2] mm: make minimum slab alignment a runtime property
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To:     Peter Collingbourne <pcc@google.com>,
        Andrey Konovalov <andreyknvl@gmail.com>,
        Hyeonggon Yoo <42.hyeyoo@gmail.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Catalin Marinas <catalin.marinas@arm.com>
Cc:     Linux ARM <linux-arm-kernel@lists.infradead.org>,
        Linux Memory Management List <linux-mm@kvack.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        penberg@kernel.org, roman.gushchin@linux.dev,
        iamjoonsoo.kim@lge.com, rientjes@google.com,
        Herbert Xu <herbert@gondor.apana.org.au>,
        Andrey Ryabinin <ryabinin.a.a@gmail.com>,
        Alexander Potapenko <glider@google.com>,
        Dmitry Vyukov <dvyukov@google.com>,
        kasan-dev <kasan-dev@googlegroups.com>,
        Eric Biederman <ebiederm@xmission.com>,
        Kees Cook <keescook@chromium.org>
References: <20220427195820.1716975-1-pcc@google.com>
 <20220427195820.1716975-2-pcc@google.com>
From:   Vlastimil Babka <vbabka@suse.cz>
In-Reply-To: <20220427195820.1716975-2-pcc@google.com>
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On 4/27/22 21:58, Peter Collingbourne wrote:
> When CONFIG_KASAN_HW_TAGS is enabled we currently increase the minimum
> slab alignment to 16. This happens even if MTE is not supported in
> hardware or disabled via kasan=off, which creates an unnecessary
> memory overhead in those cases. Eliminate this overhead by making
> the minimum slab alignment a runtime property and only aligning to
> 16 if KASAN is enabled at runtime.
> 
> On a DragonBoard 845c (non-MTE hardware) with a kernel built with
> CONFIG_KASAN_HW_TAGS, waiting for quiescence after a full Android
> boot I see the following Slab measurements in /proc/meminfo (median
> of 3 reboots):
> 
> Before: 169020 kB
> After:  167304 kB
> 
> Link: https://linux-review.googlesource.com/id/I752e725179b43b144153f4b6f584ceb646473ead
> Signed-off-by: Peter Collingbourne <pcc@google.com>
> Reviewed-by: Andrey Konovalov <andreyknvl@gmail.com>
> Reviewed-by: Hyeonggon Yoo <42.hyeyoo@gmail.com>
> Tested-by: Hyeonggon Yoo <42.hyeyoo@gmail.com>
> Acked-by: David Rientjes <rientjes@google.com>
> Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>

Acked-by: Vlastimil Babka <vbabka@suse.cz>
Andrew's fixup LGTM too.