[PATCH v2 0/2] mm: swap: mTHP swap allocator base on swap cluster order

[Chris Li <chrisl@kernel.org>]

This is the short term solutiolns "swap cluster order" listed
in my "Swap Abstraction" discussion slice 8 in the recent
LSF/MM conference.

When commit 845982eb264bc "mm: swap: allow storage of all mTHP
orders" is introduced, it only allocates the mTHP swap entries
from new empty cluster list.  It has a fragmentation issue
reported by Barry.

https://lore.kernel.org/all/CAGsJ_4zAcJkuW016Cfi6wicRr8N9X+GJJhgMQdSMp+Ah+NSgNQ@mail.gmail.com/

The mTHP allocation failure rate raises to almost 100% after a few
hours in Barry's test run.

The reason is that all the empty cluster has been exhausted while
there are planty of free swap entries to in the cluster that is
not 100% free.

Remember the swap allocation order in the cluster.
Keep track of the per order non full cluster list for later allocation.

This greatly improve the sucess rate of the mTHP swap allocation.

There is some test number in the V1 thread of this series:
https://lore.kernel.org/r/20240524-swap-allocator-v1-0-47861b423b26@kernel.org

Reported-by: Barry Song <21cnbao@gmail.com>
Signed-off-by: Chris Li <chrisl@kernel.org>
---
Changes in v2:
- Add the cluster state field to track the different phases of
  cluster allocations.
- Rename "next" to "list" for the list field, suggested by Ying.
- Update comment for the locking rules for cluster fields and listi,
  suggested by Ying.
- Nonfull list avoid cluster on the per cpu active cluster.
- Allocate from the nonfull list before attempting free list, suggested
  by Kairui.
- Link to v1: https://lore.kernel.org/r/20240524-swap-allocator-v1-0-47861b423b26@kernel.org

---
Chris Li (2):
      mm: swap: swap cluster switch to double link list
      mm: swap: mTHP allocate swap entries from nonfull list

 include/linux/swap.h |  31 +++---
 mm/swapfile.c        | 270 ++++++++++++++++++---------------------------------
 2 files changed, 107 insertions(+), 194 deletions(-)
---
base-commit: 19b8422c5bd56fb5e7085995801c6543a98bda1f
change-id: 20240523-swap-allocator-1534c480ece4

Best regards,
-- 
Chris Li <chrisl@kernel.org>