linux-kernel - Re: [PATCH v5 0/5] Implement MTE tag compression for swapped pages

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Message-ID: <8a4a6e1f-accb-92c2-ae14-9f6945e97f7a@intel.com>
Date:   Fri, 22 Sep 2023 16:40:26 +0200
From:   Alexander Lobakin <aleksander.lobakin@...el.com>
To:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Alexander Potapenko <glider@...gle.com>
CC:     <catalin.marinas@....com>, <will@...nel.org>, <pcc@...gle.com>,
        <andreyknvl@...il.com>, <linux@...musvillemoes.dk>,
        <yury.norov@...il.com>, <linux-kernel@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>, <eugenis@...gle.com>,
        <syednwaris@...il.com>, <william.gray@...aro.org>
Subject: Re: [PATCH v5 0/5] Implement MTE tag compression for swapped pages

From: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Date: Fri, 22 Sep 2023 17:35:19 +0300

> +Cc: Olek, who internally is being developed something similar to your first
> patch here.

Oh, thanks.
The patch you mentioned properly implements cross-boundary accesses,
mine does not :D
But I guess we want to keep them both to keep the latter as optimized as
the current bitmap_{get,set}_value8()?

> 
> On Fri, Sep 22, 2023 at 10:08:42AM +0200, Alexander Potapenko wrote:
>> Currently, when MTE pages are swapped out, the tags are kept in the
>> memory, occupying PAGE_SIZE/32 bytes per page. This is especially
>> problematic for devices that use zram-backed in-memory swap, because
>> tags stored uncompressed in the heap effectively reduce the available
>> amount of swap memory.
>>
>> The RLE-based algorithm suggested by Evgenii Stepanov and implemented in
>> this patch series is able to efficiently compress fixed-size tag buffers,
>> resulting in practical compression ratio between 2.5x and 4x. In most
>> cases it is possible to store the compressed data in 63-bit Xarray values,
>> resulting in no extra memory allocations.
>>
>> Our measurements show that the proposed algorithm provides better
>> compression than existing kernel compression algorithms (LZ4, LZO,
>> LZ4HC, ZSTD) can offer.

[...]

Thanks,
Olek