linux-kernel - [PATCH v3 0/2] mm: swap: mTHP swap allocator base on swap cluster order

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Date: Wed, 19 Jun 2024 02:20:28 -0700
From: Chris Li <chrisl@...nel.org>
To: Andrew Morton <akpm@...ux-foundation.org>
Cc: Kairui Song <kasong@...cent.com>, Ryan Roberts <ryan.roberts@....com>, 
 "Huang, Ying" <ying.huang@...el.com>, Kairui Song <kasong@...cent.com>, 
 Kalesh Singh <kaleshsingh@...gle.com>, linux-kernel@...r.kernel.org, 
 linux-mm@...ck.org, Chris Li <chrisl@...nel.org>, 
 Barry Song <baohua@...nel.org>
Subject: [PATCH v3 0/2] mm: swap: mTHP swap allocator base on swap cluster
 order

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 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.

User impact: For users that allocate and free mix order mTHP swapping,
It greatly improves the success rate of the mTHP swap allocation after the
initial phase.

Barry provides a test program to show the effect:
https://lore.kernel.org/linux-mm/20240615084714.37499-1-21cnbao@gmail.com/

Without:
$ mthp-swapout                                                          
Iteration 1: swpout inc: 222, swpout fallback inc: 0, Fallback percentage: 0.00%   
Iteration 2: swpout inc: 219, swpout fallback inc: 0, Fallback percentage: 0.00%                                                    
Iteration 3: swpout inc: 222, swpout fallback inc: 0, Fallback percentage: 0.00%   
Iteration 4: swpout inc: 219, swpout fallback inc: 0, Fallback percentage: 0.00%            
Iteration 5: swpout inc: 110, swpout fallback inc: 117, Fallback percentage: 51.54%                                                 
Iteration 6: swpout inc: 0, swpout fallback inc: 230, Fallback percentage: 100.00%          
Iteration 7: swpout inc: 0, swpout fallback inc: 229, Fallback percentage: 100.00% 
Iteration 8: swpout inc: 0, swpout fallback inc: 223, Fallback percentage: 100.00%                                                  
Iteration 9: swpout inc: 0, swpout fallback inc: 224, Fallback percentage: 100.00%                                                  
Iteration 10: swpout inc: 0, swpout fallback inc: 216, Fallback percentage: 100.00%                                                 
Iteration 11: swpout inc: 0, swpout fallback inc: 212, Fallback percentage: 100.00%                                                 
Iteration 12: swpout inc: 0, swpout fallback inc: 224, Fallback percentage: 100.00%                                                 
Iteration 13: swpout inc: 0, swpout fallback inc: 214, Fallback percentage: 100.00%        

$ mthp-swapout -s
Iteration 1: swpout inc: 222, swpout fallback inc: 0, Fallback percentage: 0.00%
Iteration 2: swpout inc: 227, swpout fallback inc: 0, Fallback percentage: 0.00%
Iteration 3: swpout inc: 222, swpout fallback inc: 0, Fallback percentage: 0.00%
Iteration 4: swpout inc: 224, swpout fallback inc: 0, Fallback percentage: 0.00%
Iteration 5: swpout inc: 33, swpout fallback inc: 197, Fallback percentage: 85.65%
Iteration 6: swpout inc: 0, swpout fallback inc: 229, Fallback percentage: 100.00%
Iteration 7: swpout inc: 0, swpout fallback inc: 223, Fallback percentage: 100.00%
Iteration 8: swpout inc: 0, swpout fallback inc: 219, Fallback percentage: 100.00%
Iteration 9: swpout inc: 0, swpout fallback inc: 212, Fallback percentage: 100.00%

With:
$ mthp-swapout       
Iteration 1: swpout inc: 222, swpout fallback inc: 0, Fallback percentage: 0.00%                                                    
Iteration 2: swpout inc: 219, swpout fallback inc: 0, Fallback percentage: 0.00%                                                    
Iteration 3: swpout inc: 222, swpout fallback inc: 0, Fallback percentage: 0.00%                                                    
Iteration 4: swpout inc: 219, swpout fallback inc: 0, Fallback percentage: 0.00%       
Iteration 5: swpout inc: 227, swpout fallback inc: 0, Fallback percentage: 0.00% 
Iteration 6: swpout inc: 230, swpout fallback inc: 0, Fallback percentage: 0.00%            
...
Iteration 94: swpout inc: 224, swpout fallback inc: 0, Fallback percentage: 0.00%
Iteration 95: swpout inc: 221, swpout fallback inc: 0, Fallback percentage: 0.00%
Iteration 96: swpout inc: 229, swpout fallback inc: 0, Fallback percentage: 0.00%
Iteration 97: swpout inc: 219, swpout fallback inc: 0, Fallback percentage: 0.00%
Iteration 98: swpout inc: 222, swpout fallback inc: 0, Fallback percentage: 0.00%
Iteration 99: swpout inc: 223, swpout fallback inc: 0, Fallback percentage: 0.00%
Iteration 100: swpout inc: 224, swpout fallback inc: 0, Fallback percentage: 0.00%

$ mthp-swapout -s
Iteration 1: swpout inc: 222, swpout fallback inc: 0, Fallback percentage: 0.00%
Iteration 2: swpout inc: 227, swpout fallback inc: 0, Fallback percentage: 0.00%
Iteration 3: swpout inc: 222, swpout fallback inc: 0, Fallback percentage: 0.00%
Iteration 4: swpout inc: 224, swpout fallback inc: 0, Fallback percentage: 0.00%
Iteration 5: swpout inc: 230, swpout fallback inc: 0, Fallback percentage: 0.00%
Iteration 6: swpout inc: 229, swpout fallback inc: 0, Fallback percentage: 0.00%
Iteration 7: swpout inc: 223, swpout fallback inc: 0, Fallback percentage: 0.00%
Iteration 8: swpout inc: 219, swpout fallback inc: 0, Fallback percentage: 0.00%
...
Iteration 94: swpout inc: 223, swpout fallback inc: 0, Fallback percentage: 0.00%
Iteration 95: swpout inc: 212, swpout fallback inc: 0, Fallback percentage: 0.00%
Iteration 96: swpout inc: 220, swpout fallback inc: 0, Fallback percentage: 0.00%
Iteration 97: swpout inc: 220, swpout fallback inc: 0, Fallback percentage: 0.00%
Iteration 98: swpout inc: 216, swpout fallback inc: 0, Fallback percentage: 0.00%
Iteration 99: swpout inc: 223, swpout fallback inc: 0, Fallback percentage: 0.00%
Iteration 100: swpout inc: 225, swpout fallback inc: 0, Fallback percentage: 0.00%

Reported-by: Barry Song <21cnbao@...il.com>
Signed-off-by: Chris Li <chrisl@...nel.org>
---
Changes in v3:
- Using V1 as base.
- Rename "next" to "list" for the list field, suggested by Ying.
- Update comment for the locking rules for cluster fields and list,
  suggested by Ying.
- Allocate from the nonfull list before attempting free list, suggested
  by Kairui.
- Link to v2: https://lore.kernel.org/r/20240614-swap-allocator-v2-0-2a513b4a7f2f@kernel.org

Changes in v2:
- Abandoned.
- 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 |  30 +++----
 mm/swapfile.c        | 248 +++++++++++++++++----------------------------------
 2 files changed, 95 insertions(+), 183 deletions(-)
---
base-commit: 19b8422c5bd56fb5e7085995801c6543a98bda1f
change-id: 20240523-swap-allocator-1534c480ece4

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