linux-kernel - [PATCH v3 0/6] large folios swap-in: handle refault cases first

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Date: Fri,  3 May 2024 12:50:17 +1200
From: Barry Song <21cnbao@...il.com>
To: akpm@...ux-foundation.org,
	linux-mm@...ck.org
Cc: baolin.wang@...ux.alibaba.com,
	chrisl@...nel.org,
	david@...hat.com,
	hanchuanhua@...o.com,
	hannes@...xchg.org,
	hughd@...gle.com,
	kasong@...cent.com,
	linux-kernel@...r.kernel.org,
	ryan.roberts@....com,
	surenb@...gle.com,
	v-songbaohua@...o.com,
	willy@...radead.org,
	xiang@...nel.org,
	ying.huang@...el.com,
	yosryahmed@...gle.com,
	yuzhao@...gle.com,
	ziy@...dia.com
Subject: [PATCH v3 0/6] large folios swap-in: handle refault cases first

From: Barry Song <v-songbaohua@...o.com>

This patch is extracted from the large folio swapin series[1], primarily addressing
the handling of scenarios involving large folios in the swap cache. Currently, it is
particularly focused on addressing the refaulting of mTHP, which is still undergoing
reclamation. This approach aims to streamline code review and expedite the integration
of this segment into the MM tree.

It relies on Ryan's swap-out series[2], leveraging the helper function
swap_pte_batch() introduced by that series.

Presently, do_swap_page only encounters a large folio in the swap
cache before the large folio is released by vmscan. However, the code
should remain equally useful once we support large folio swap-in via
swapin_readahead(). This approach can effectively reduce page faults
and eliminate most redundant checks and early exits for MTE restoration
in recent MTE patchset[3].

The large folio swap-in for SWP_SYNCHRONOUS_IO and swapin_readahead()
will be split into separate patch sets and sent at a later time.

-v3:
 - optimize swap_free_nr using bitmap with single one "long"; "Huang, Ying"
 - drop swap_free() as suggested by "Huang, Ying", now hibernation can get
   batched;
 - lots of cleanup in do_swap_page() as commented by Ryan Roberts and "Huang,
   Ying";
 - handle arch_do_swap_page() with nr pages though the only platform which
   needs it, sparc, doesn't support THP_SWAPOUT as suggested by "Huang,
   Ying";
 - introduce pte_move_swp_offset() as suggested by "Huang, Ying";
 - drop the "any_shared" of checking swap entries with respect to David's
   comment;
 - drop the counter of swapin_refault and keep it for debug purpose per
   Ying
 - collect reviewed-by tags

-v2:
 - rebase on top of mm-unstable in which Ryan's swap_pte_batch() has changed
   a lot.
 - remove folio_add_new_anon_rmap() for !folio_test_anon()
   as currently large folios are always anon(refault).
 - add mTHP swpin refault counters
  Link:
  https://lore.kernel.org/linux-mm/20240409082631.187483-1-21cnbao@gmail.com/

-v1:
  Link: https://lore.kernel.org/linux-mm/20240402073237.240995-1-21cnbao@gmail.com/

Differences with the original large folios swap-in series
 - collect r-o-b, acked;
 - rename swap_nr_free to swap_free_nr, according to Ryan;
 - limit the maximum kernel stack usage for swap_free_nr, Ryan;
 - add output argument in swap_pte_batch to expose if all entries are
   exclusive
 - many clean refinements, handle the corner case folio's virtual addr
   might not be naturally aligned

[1] https://lore.kernel.org/linux-mm/20240304081348.197341-1-21cnbao@gmail.com/
[2] https://lore.kernel.org/linux-mm/20240408183946.2991168-1-ryan.roberts@arm.com/
[3] https://lore.kernel.org/linux-mm/20240322114136.61386-1-21cnbao@gmail.com/

Barry Song (3):
  mm: remove swap_free() and always use swap_free_nr()
  mm: introduce pte_move_swp_offset() helper which can move offset
    bidirectionally
  mm: introduce arch_do_swap_page_nr() which allows restore metadata for
    nr pages

Chuanhua Han (3):
  mm: swap: introduce swap_free_nr() for batched swap_free()
  mm: swap: make should_try_to_free_swap() support large-folio
  mm: swap: entirely map large folios found in swapcache

 include/linux/pgtable.h | 26 ++++++++++++++----
 include/linux/swap.h    |  4 +--
 kernel/power/swap.c     |  7 ++---
 mm/internal.h           | 25 ++++++++++++++---
 mm/memory.c             | 61 +++++++++++++++++++++++++++++++++--------
 mm/rmap.c               |  4 +--
 mm/shmem.c              |  4 +--
 mm/swapfile.c           | 50 +++++++++++++++++++++++++++++----
 8 files changed, 143 insertions(+), 38 deletions(-)

-- 
2.34.1