Hi,
Existing zsmalloc page fullness grouping leads to suboptimal page
selection for both zs_malloc() and zs_compact(). This patchset
reworks zsmalloc fullness grouping/classification.
Additinally it also implements new compaction algorithm that is
expected to use CPU-cycles (as it potentially does fewer memcpy-s
in zs_object_copy()).
TEST
====
It's very challenging to reliably test this series. I ended up
developing my own synthetic test that has 100% reproducibility.
The test generates significan fragmentation (for each size class)
and then performs compaction for each class individually and tracks
the number of memcpy() in zs_object_copy(), so that we can compare
the amount work compaction does on per-class basis.
Total amount of work (zram mm_stat objs_moved)
----------------------------------------------
Old fullness grouping, old compaction algorithm:
323977 memcpy() in zs_object_copy().
Old fullness grouping, new compaction algorithm:
262944 memcpy() in zs_object_copy().
New fullness grouping, new compaction algorithm:
213978 memcpy() in zs_object_copy().
Per-class compaction memcpy() comparison (T-test)
-------------------------------------------------
x Old fullness grouping, old compaction algorithm
+ Old fullness grouping, new compaction algorithm
N Min Max Median Avg Stddev
x 140 349 3513 2461 2314.1214 806.03271
+ 140 289 2778 2006 1878.1714 641.02073
Difference at 95.0% confidence
-435.95 +/- 170.595
-18.8387% +/- 7.37193%
(Student's t, pooled s = 728.216)
x Old fullness grouping, old compaction algorithm
+ New fullness grouping, new compaction algorithm
N Min Max Median Avg Stddev
x 140 349 3513 2461 2314.1214 806.03271
+ 140 226 2279 1644 1528.4143 524.85268
Difference at 95.0% confidence
-785.707 +/- 159.331
-33.9527% +/- 6.88516%
(Student's t, pooled s = 680.132)
Sergey Senozhatsky (6):
zsmalloc: remove insert_zspage() ->inuse optimization
zsmalloc: remove stat and fullness enums
zsmalloc: fine-grained inuse ratio based fullness grouping
zsmalloc: rework compaction algorithm
zsmalloc: extend compaction statistics
zram: show zsmalloc objs_moved stat in mm_stat
Documentation/admin-guide/blockdev/zram.rst | 1 +
drivers/block/zram/zram_drv.c | 5 +-
include/linux/zsmalloc.h | 2 +
mm/zsmalloc.c | 365 ++++++++++----------
4 files changed, 188 insertions(+), 185 deletions(-)
--
2.39.2.637.g21b0678d19-goog
