[PATCH RFC 0/6] mm: support large folios swap-in

Barry Song
2024-01-18T11:11:04Z

On an embedded system like Android, more than half of anon memory is actually
in swap devices such as zRAM. For example, while an app is switched to back-
ground, its most memory might be swapped-out.

Now we have mTHP features, unfortunately, if we don't support large folios
swap-in, once those large folios are swapped-out, we immediately lose the
performance gain we can get through large folios and hardware optimization
such as CONT-PTE.

In theory, we don't need to rely on Ryan's swap out patchset[1]. That is to say,
before swap-out, if some memory were normal pages, but when swapping in, we
can also swap-in them as large folios. But this might require I/O happen at
some random places in swap devices. So we limit the large folios swap-in to
those areas which were large folios before swapping-out, aka, swaps are also
contiguous in hardware. On the other hand, in OPPO's product, we've deployed
anon large folios on millions of phones[2]. we enhanced zsmalloc and zRAM to
compress and decompress large folios as a whole, which help improve compression
ratio and decrease CPU consumption significantly. In zsmalloc and zRAM we can
save large objects whose original size are 64KiB for example. So it is also a
better choice for us to only swap-in large folios for those compressed large
objects as a large folio can be decompressed all together.

Note I am moving my previous "arm64: mm: swap: support THP_SWAP on hardware
with MTE" to this series as it might help review.

[1] [PATCH v3 0/4] Swap-out small-sized THP without splitting
https://lore.kernel.org/linux-mm/20231025144546.577640-1-ryan.roberts@arm.com/
[2] OnePlusOSS / android_kernel_oneplus_sm8550
https://github.com/OnePlusOSS/android_kernel_oneplus_sm8550/tree/oneplus/sm8550_u_14.0.0_oneplus11

Barry Song (2):
arm64: mm: swap: support THP_SWAP on hardware with MTE
mm: rmap: weaken the WARN_ON in __folio_add_anon_rmap()

Chuanhua Han (4):
mm: swap: introduce swap_nr_free() for batched swap_free()
mm: swap: make should_try_to_free_swap() support large-folio
mm: support large folios swapin as a whole
mm: madvise: don't split mTHP for MADV_PAGEOUT

arch/arm64/include/asm/pgtable.h | 21 ++----
arch/arm64/mm/mteswap.c | 42 ++++++++++++
include/asm-generic/tlb.h | 10 +++
include/linux/huge_mm.h | 12 ----
include/linux/pgtable.h | 62 ++++++++++++++++-
include/linux/swap.h | 6 ++
mm/madvise.c | 48 ++++++++++++++
mm/memory.c | 110 ++++++++++++++++++++++++++-----
mm/page_io.c | 2 +-
mm/rmap.c | 5 +-
mm/swap_slots.c | 2 +-
mm/swapfile.c | 29 ++++++++
12 files changed, 301 insertions(+), 48 deletions(-)

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2.34.1