Messages in this thread | | | Date | Tue, 11 Jul 2023 16:42:28 +0200 | Subject | [Resend v1 0/5] Implement MTE tag compression for swapped pages | From | Alexander Potapenko <> |
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Currently, when MTE pages are swapped out, the tags are kept in the memory, occupying 128 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 EA0 algorithm suggested by Evgenii Stepanov and implemented in this patch series is able to efficiently compress 128-byte tag buffers, resulting in practical compression ratio between 2.5x and 20x. 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 EA0 provides better compression than existing kernel compression algorithms (LZ4, LZO, LZ4HC, ZSTD) can offer, because EA0 specifically targets 128-byte buffers.
To implement compression/decompression, we introduce <linux/bitqueue.h>, which provides a simple bit queue interface.
We refactor arch/arm64/mm/mteswap.c to support both the compressed (CONFIG_ARM64_MTE_COMP) and non-compressed case. For the former, in addition to tag compression, we move tag allocation from kmalloc() to separate kmem caches, providing greater locality and relaxing the alignment requirements.
Alexander Potapenko (5): linux/bitqueue.h: add the bit queue implementation linux/bitqueue.h: add a KUnit test for bitqueue.h arm64: mte: implement CONFIG_ARM64_MTE_COMP arm64: mte: add a test for MTE tags compression arm64: mte: add compression support to mteswap.c
arch/arm64/Kconfig | 20 ++ arch/arm64/include/asm/mtecomp.h | 60 +++++ arch/arm64/mm/Makefile | 7 + arch/arm64/mm/mtecomp.c | 398 +++++++++++++++++++++++++++++++ arch/arm64/mm/mteswap.c | 19 +- arch/arm64/mm/mteswap.h | 12 + arch/arm64/mm/mteswap_comp.c | 50 ++++ arch/arm64/mm/mteswap_nocomp.c | 37 +++ arch/arm64/mm/test_mtecomp.c | 175 ++++++++++++++ include/linux/bitqueue.h | 144 +++++++++++ lib/Kconfig.debug | 8 + lib/Makefile | 1 + lib/test_bitqueue.c | 244 +++++++++++++++++++ 13 files changed, 1164 insertions(+), 11 deletions(-) create mode 100644 arch/arm64/include/asm/mtecomp.h create mode 100644 arch/arm64/mm/mtecomp.c create mode 100644 arch/arm64/mm/mteswap.h create mode 100644 arch/arm64/mm/mteswap_comp.c create mode 100644 arch/arm64/mm/mteswap_nocomp.c create mode 100644 arch/arm64/mm/test_mtecomp.c create mode 100644 include/linux/bitqueue.h create mode 100644 lib/test_bitqueue.c
-- 2.41.0.255.g8b1d071c50-goog
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