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

[Alexander Lobakin]

From: Andy Shevchenko <andriy.shevchenko@xxxxxxxxxxxxxxx>
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