[PATCH 0/2] mm, swap: improve cluster scan strategy

[Kairui Song <ryncsn@gmail.com>]

From: Kairui Song <kasong@tencent.com>

This series improves the large allocation performance and reduces
the failure rate. Some design of the cluster alloactor was later
found to be improvable after thorough testing.

For example, build kernel test with make -j96 and 10G ZRAM with 64kB
mTHP enabled shows better performance and a lower failure rate:

Before: sys time: 10230.22s  64kB/swpout: 1793044  64kB/swpout_fallback: 17653
After:  sys time: 5538.3s    64kB/swpout: 1813133  64kB/swpout_fallback: 0

System time is cut in half, and the failure rate drops to zero. Larger
allocations in a hybrid workload also showed a major improvement:

512kB swap failure rate:
Before: swpout:11971  swpout_fallback:2218
After:  swpout:14606  swpout_fallback:4

2M swap failure rate:
Before: swpout:12     swpout_fallback:1578
After:  swpout:1253   swpout_fallback:15

Kairui Song (2):
  mm, swap: don't scan every fragment cluster
  mm, swap: prefer nonfull over free clusters

 include/linux/swap.h |  1 -
 mm/swapfile.c        | 68 +++++++++++++++++++++++---------------------
 2 files changed, 36 insertions(+), 33 deletions(-)

-- 
2.50.1