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Message-ID: <20231103160335.2464561-1-glider@google.com>
Date: Fri, 3 Nov 2023 17:03:32 +0100
From: Alexander Potapenko <glider@...gle.com>
To: glider@...gle.com, catalin.marinas@....com, will@...nel.org,
pcc@...gle.com, andreyknvl@...il.com,
andriy.shevchenko@...ux.intel.com, aleksander.lobakin@...el.com,
linux@...musvillemoes.dk, yury.norov@...il.com,
alexandru.elisei@....com
Cc: linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
eugenis@...gle.com, syednwaris@...il.com, william.gray@...aro.org
Subject: [PATCH v8 0/3] Implement MTE tag compression for swapped pages
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 of 2x. In many cases it is
possible to store the compressed data in 63-bit Xarray values, resulting
in no extra memory allocations.
This patch series depends on "lib/bitmap: add bitmap_{read,write}()"
(https://lore.kernel.org/linux-arm-kernel/20231030153210.139512-1-glider@google.com/T/)
that is mailed separately.
v8:
- split off the bitmap_read()/bitmap_write() series
- simplified the compression logic (only compress data if it fits into
a pointer)
v7:
- fixed comments by Yury Norov, Andy Shevchenko, Rasmus Villemoes
- added perf tests for bitmap_read()/bitmap_write()
- more efficient bitmap_write() implementation (meant to be sent in v5)
v6:
- fixed comments by Yury Norov
- fixed handling of sizes divisible by MTE_GRANULES_PER_PAGE / 2
(caught while testing on a real device)
v5:
- fixed comments by Andy Shevchenko, Catalin Marinas, and Yury Norov
- added support for 16K- and 64K pages
- more efficient bitmap_write() implementation
v4:
- fixed a bunch of comments by Andy Shevchenko and Yury Norov
- added Documentation/arch/arm64/mte-tag-compression.rst
v3:
- as suggested by Andy Shevchenko, use
bitmap_get_value()/bitmap_set_value() written by Syed Nayyar Waris
- switched to unsigned long to reduce typecasts
- simplified the compression code
v2:
- as suggested by Yuri Norov, replace the poorly implemented struct
bitq with <linux/bitmap.h>
Alexander Potapenko (3):
arm64: mte: implement CONFIG_ARM64_MTE_COMP
arm64: mte: add a test for MTE tags compression
arm64: mte: add compression support to mteswap.c
Documentation/arch/arm64/index.rst | 1 +
.../arch/arm64/mte-tag-compression.rst | 154 ++++++++
arch/arm64/Kconfig | 21 +
arch/arm64/include/asm/mtecomp.h | 39 ++
arch/arm64/mm/Makefile | 2 +
arch/arm64/mm/mtecomp.c | 257 +++++++++++++
arch/arm64/mm/mtecomp.h | 12 +
arch/arm64/mm/mteswap.c | 88 ++++-
arch/arm64/mm/test_mtecomp.c | 364 ++++++++++++++++++
9 files changed, 934 insertions(+), 4 deletions(-)
create mode 100644 Documentation/arch/arm64/mte-tag-compression.rst
create mode 100644 arch/arm64/include/asm/mtecomp.h
create mode 100644 arch/arm64/mm/mtecomp.c
create mode 100644 arch/arm64/mm/mtecomp.h
create mode 100644 arch/arm64/mm/test_mtecomp.c
--
2.42.0.869.gea05f2083d-goog
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