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Date:   Tue, 12 Dec 2023 17:17:38 +0000
From:   Catalin Marinas <catalin.marinas@arm.com>
To:     Alexander Potapenko <glider@google.com>
Cc:     will@kernel.org, pcc@google.com, andreyknvl@gmail.com,
        andriy.shevchenko@linux.intel.com, aleksander.lobakin@intel.com,
        linux@rasmusvillemoes.dk, yury.norov@gmail.com,
        alexandru.elisei@arm.com, linux-kernel@vger.kernel.org,
        linux-arm-kernel@lists.infradead.org, eugenis@google.com,
        syednwaris@gmail.com, william.gray@linaro.org
Subject: Re: [PATCH v9 3/4] arm64: mte: add compression support to mteswap.c
Message-ID: <ZXiVsiPj7iULFCY5@arm.com>
References: <20231113105234.32058-1-glider@google.com>
 <20231113105234.32058-4-glider@google.com>
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On Mon, Nov 13, 2023 at 11:52:32AM +0100, Alexander Potapenko wrote:
> Update mteswap.c to perform inline compression of memory tags when
> possible.
> 
> If CONFIG_ARM64_MTE_COMP is enabled, mteswap.c will attempt to compress
> saved tags for a struct page and store them directly in Xarray entry
> instead of wasting heap space.
> 
> Soon after booting Android, tag compression saves ~2x memory previously
> spent by mteswap.c on tag allocations. On a moderately loaded device with
> ~20% tagged pages, this leads to saving several megabytes of kernel heap:
> 
>   # cat /sys/kernel/debug/mteswap/stats
>   8 bytes:	102496 allocations,	67302 deallocations
>   128 bytes:	212234 allocations,	178278 deallocations
>   uncompressed tag storage size:	8851200
>   compressed tag storage size:	4346368
> 
> (statistics collection is introduced in the following patch)
> 
> Signed-off-by: Alexander Potapenko <glider@google.com>

Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>