Changes in v2: - Fix the comments of try_to_merge_with_zero_page(), per David. - Drop the last one patch in this version since it's a very rare case and hard to testing to prove. - Rebase on the latest mm/mm-stable branch. - Link to v1: https://lore.kernel.org/r/20240524-b4-ksm-scan-optimize-v1-0-053b31bd7ab4@xxxxxxxxx Hello, This series mainly optimizes cmp_and_merge_page() to have more efficient separate code flow for ksm page and non-ksm anon page. - ksm page: don't need to calculate the checksum obviously. - anon page: don't need to search stable tree if changing fast and try to merge with zero page before searching ksm page on stable tree. Please see the patch-2 for details. Patch-3 is cleanup also a little optimization for the chain()/chain_prune interfaces, which made the stable_tree_search()/stable_tree_insert() over complex. I have done simple testing using "hackbench -g 1 -l 300000" (maybe I need to use a better workload) on my machine, have seen a little CPU usage decrease of ksmd and some improvements of cmp_and_merge_page() latency: We can see the latency of cmp_and_merge_page() when handling non-ksm anon pages has been improved. Thanks for review and comments! Before: - ksm page [128, 256) 21 | | [256, 512) 12509 |@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@| [512, 1K) 769 |@@@ | [1K, 2K) 99 | | [2K, 4K) 4 | | [4K, 8K) 2 | | [8K, 16K) 8 | | - anon page [512, 1K) 19 | | [1K, 2K) 7160 |@@@@@@@@@@@ | [2K, 4K) 33516 |@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@| [4K, 8K) 33172 |@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@ | [8K, 16K) 11305 |@@@@@@@@@@@@@@@@@ | [16K, 32K) 1303 |@@ | [32K, 64K) 16 | | [64K, 128K) 6 | | [128K, 256K) 6 | | [256K, 512K) 9 | | [512K, 1M) 3 | | [1M, 2M) 2 | | [2M, 4M) 1 | | After: - ksm page [128, 256) 9 | | [256, 512) 915 |@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@| [512, 1K) 41 |@@ | [1K, 2K) 1 | | [2K, 4K) 1 | | - anon page [512, 1K) 374 | | [1K, 2K) 5367 |@@@@ | [2K, 4K) 64362 |@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@| [4K, 8K) 27721 |@@@@@@@@@@@@@@@@@@@@@@ | [8K, 16K) 1047 | | [16K, 32K) 63 | | [32K, 64K) 7 | | [64K, 128K) 6 | | [128K, 256K) 5 | | [256K, 512K) 3 | | [512K, 1M) 1 | | Signed-off-by: Chengming Zhou <chengming.zhou@xxxxxxxxx> --- Chengming Zhou (3): mm/ksm: refactor out try_to_merge_with_zero_page() mm/ksm: don't waste time searching stable tree for fast changing page mm/ksm: optimize the chain()/chain_prune() interfaces mm/ksm.c | 250 +++++++++++++++++++++------------------------------------------ 1 file changed, 82 insertions(+), 168 deletions(-) --- base-commit: 6ba59ff4227927d3a8530fc2973b80e94b54d58f change-id: 20240621-b4-ksm-scan-optimize-e614a3a52217 Best regards, -- Chengming Zhou <chengming.zhou@xxxxxxxxx>
