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

[Barry Song <21cnbao@gmail.com>]

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(-)

-- 
2.34.1