* [PATCH 1/2] zsmalloc: document new fullness grouping
2023-03-25 2:46 [PATCH 0/2] zsmalloc: minor documentation updates Sergey Senozhatsky
@ 2023-03-25 2:46 ` Sergey Senozhatsky
2023-03-25 2:46 ` [PATCH 2/2] zsmalloc: document freeable stats Sergey Senozhatsky
2023-03-25 19:54 ` [PATCH 0/2] zsmalloc: minor documentation updates Andrew Morton
2 siblings, 0 replies; 5+ messages in thread
From: Sergey Senozhatsky @ 2023-03-25 2:46 UTC (permalink / raw)
To: Andrew Morton, Minchan Kim; +Cc: linux-kernel, linux-mm, Sergey Senozhatsky
Update documentation and reflect new zspages fullness grouping
(we don't use almost_empty and almost_full anymore).
Signed-off-by: Sergey Senozhatsky <senozhatsky@chromium.org>
---
Documentation/mm/zsmalloc.rst | 133 +++++++++++++++++++---------------
1 file changed, 74 insertions(+), 59 deletions(-)
diff --git a/Documentation/mm/zsmalloc.rst b/Documentation/mm/zsmalloc.rst
index 64d127bfc221..3c6bf639887f 100644
--- a/Documentation/mm/zsmalloc.rst
+++ b/Documentation/mm/zsmalloc.rst
@@ -39,13 +39,12 @@ With CONFIG_ZSMALLOC_STAT, we could see zsmalloc internal information via
# cat /sys/kernel/debug/zsmalloc/zram0/classes
- class size almost_full almost_empty obj_allocated obj_used pages_used pages_per_zspage
+ class size 10% 20% 30% 40% 50% 60% 70% 80% 90% 99% 100% obj_allocated obj_used pages_used pages_per_zspage freeable
...
...
- 9 176 0 1 186 129 8 4
- 10 192 1 0 2880 2872 135 3
- 11 208 0 1 819 795 42 2
- 12 224 0 1 219 159 12 4
+ 30 512 0 12 4 1 0 1 0 0 1 0 414 3464 3346 433 1 14
+ 31 528 2 7 2 2 1 0 1 0 0 2 117 4154 3793 536 4 44
+ 32 544 6 3 4 1 2 1 0 0 0 1 260 4170 3965 556 2 26
...
...
@@ -54,10 +53,28 @@ class
index
size
object size zspage stores
-almost_empty
- the number of ZS_ALMOST_EMPTY zspages(see below)
-almost_full
- the number of ZS_ALMOST_FULL zspages(see below)
+10%
+ the number of zspages with usage ratio less than 10% (see below)
+20%
+ the number of zspages with usage ratio between 10% and 20%
+30%
+ the number of zspages with usage ratio between 20% and 30%
+40%
+ the number of zspages with usage ratio between 30% and 40%
+50%
+ the number of zspages with usage ratio between 40% and 50%
+60%
+ the number of zspages with usage ratio between 50% and 60%
+70%
+ the number of zspages with usage ratio between 60% and 70%
+80%
+ the number of zspages with usage ratio between 70% and 80%
+90%
+ the number of zspages with usage ratio between 80% and 90%
+99%
+ the number of zspages with usage ratio between 90% and 99%
+100%
+ the number of zspages with usage ratio 100%
obj_allocated
the number of objects allocated
obj_used
@@ -67,18 +84,11 @@ pages_used
pages_per_zspage
the number of 0-order pages to make a zspage
-We assign a zspage to ZS_ALMOST_EMPTY fullness group when n <= N / f, where
-
-* n = number of allocated objects
-* N = total number of objects zspage can store
-* f = fullness_threshold_frac(ie, 4 at the moment)
-
-Similarly, we assign zspage to:
-
-* ZS_ALMOST_FULL when n > N / f
-* ZS_EMPTY when n == 0
-* ZS_FULL when n == N
-
+Each zspage maintains inuse counter which keeps track of the number of
+objects stored in the zspage. The inuse counter determines the zspage's
+"fullness group" which is calculated as the ratio of the "inuse" objects to
+the total number of objects the zspage can hold (objs_per_zspage). The
+closer the inuse counter is to objs_per_zspage, the better.
Internals
=========
@@ -94,10 +104,10 @@ of objects that each zspage can store.
For instance, consider the following size classes:::
- class size almost_full almost_empty obj_allocated obj_used pages_used pages_per_zspage freeable
+ class size 10% .... 100% obj_allocated obj_used pages_used pages_per_zspage freeable
...
- 94 1536 0 0 0 0 0 3 0
- 100 1632 0 0 0 0 0 2 0
+ 94 1536 0 .... 0 0 0 0 3 0
+ 100 1632 0 .... 0 0 0 0 2 0
...
@@ -134,10 +144,11 @@ reduces memory wastage.
Let's take a closer look at the bottom of `/sys/kernel/debug/zsmalloc/zramX/classes`:::
- class size almost_full almost_empty obj_allocated obj_used pages_used pages_per_zspage freeable
+ class size 10% .... 100% obj_allocated obj_used pages_used pages_per_zspage freeable
+
...
- 202 3264 0 0 0 0 0 4 0
- 254 4096 0 0 0 0 0 1 0
+ 202 3264 0 .. 0 0 0 0 4 0
+ 254 4096 0 .. 0 0 0 0 1 0
...
Size class #202 stores objects of size 3264 bytes and has a maximum of 4 pages
@@ -151,40 +162,42 @@ efficient storage of large objects.
For zspage chain size of 8, huge class watermark becomes 3632 bytes:::
- class size almost_full almost_empty obj_allocated obj_used pages_used pages_per_zspage freeable
+ class size 10% .... 100% obj_allocated obj_used pages_used pages_per_zspage freeable
+
...
- 202 3264 0 0 0 0 0 4 0
- 211 3408 0 0 0 0 0 5 0
- 217 3504 0 0 0 0 0 6 0
- 222 3584 0 0 0 0 0 7 0
- 225 3632 0 0 0 0 0 8 0
- 254 4096 0 0 0 0 0 1 0
+ 202 3264 0 .. 0 0 0 0 4 0
+ 211 3408 0 .. 0 0 0 0 5 0
+ 217 3504 0 .. 0 0 0 0 6 0
+ 222 3584 0 .. 0 0 0 0 7 0
+ 225 3632 0 .. 0 0 0 0 8 0
+ 254 4096 0 .. 0 0 0 0 1 0
...
For zspage chain size of 16, huge class watermark becomes 3840 bytes:::
- class size almost_full almost_empty obj_allocated obj_used pages_used pages_per_zspage freeable
+ class size 10% .... 100% obj_allocated obj_used pages_used pages_per_zspage freeable
+
...
- 202 3264 0 0 0 0 0 4 0
- 206 3328 0 0 0 0 0 13 0
- 207 3344 0 0 0 0 0 9 0
- 208 3360 0 0 0 0 0 14 0
- 211 3408 0 0 0 0 0 5 0
- 212 3424 0 0 0 0 0 16 0
- 214 3456 0 0 0 0 0 11 0
- 217 3504 0 0 0 0 0 6 0
- 219 3536 0 0 0 0 0 13 0
- 222 3584 0 0 0 0 0 7 0
- 223 3600 0 0 0 0 0 15 0
- 225 3632 0 0 0 0 0 8 0
- 228 3680 0 0 0 0 0 9 0
- 230 3712 0 0 0 0 0 10 0
- 232 3744 0 0 0 0 0 11 0
- 234 3776 0 0 0 0 0 12 0
- 235 3792 0 0 0 0 0 13 0
- 236 3808 0 0 0 0 0 14 0
- 238 3840 0 0 0 0 0 15 0
- 254 4096 0 0 0 0 0 1 0
+ 202 3264 0 .. 0 0 0 0 4 0
+ 206 3328 0 .. 0 0 0 0 13 0
+ 207 3344 0 .. 0 0 0 0 9 0
+ 208 3360 0 .. 0 0 0 0 14 0
+ 211 3408 0 .. 0 0 0 0 5 0
+ 212 3424 0 .. 0 0 0 0 16 0
+ 214 3456 0 .. 0 0 0 0 11 0
+ 217 3504 0 .. 0 0 0 0 6 0
+ 219 3536 0 .. 0 0 0 0 13 0
+ 222 3584 0 .. 0 0 0 0 7 0
+ 223 3600 0 .. 0 0 0 0 15 0
+ 225 3632 0 .. 0 0 0 0 8 0
+ 228 3680 0 .. 0 0 0 0 9 0
+ 230 3712 0 .. 0 0 0 0 10 0
+ 232 3744 0 .. 0 0 0 0 11 0
+ 234 3776 0 .. 0 0 0 0 12 0
+ 235 3792 0 .. 0 0 0 0 13 0
+ 236 3808 0 .. 0 0 0 0 14 0
+ 238 3840 0 .. 0 0 0 0 15 0
+ 254 4096 0 .. 0 0 0 0 1 0
...
Overall the combined zspage chain size effect on zsmalloc pool configuration:::
@@ -214,9 +227,10 @@ zram as a build artifacts storage (Linux kernel compilation).
zsmalloc classes stats:::
- class size almost_full almost_empty obj_allocated obj_used pages_used pages_per_zspage freeable
+ class size 10% .... 100% obj_allocated obj_used pages_used pages_per_zspage freeable
+
...
- Total 13 51 413836 412973 159955 3
+ Total 13 .. 51 413836 412973 159955 3
zram mm_stat:::
@@ -227,9 +241,10 @@ zram as a build artifacts storage (Linux kernel compilation).
zsmalloc classes stats:::
- class size almost_full almost_empty obj_allocated obj_used pages_used pages_per_zspage freeable
+ class size 10% .... 100% obj_allocated obj_used pages_used pages_per_zspage freeable
+
...
- Total 18 87 414852 412978 156666 0
+ Total 18 .. 87 414852 412978 156666 0
zram mm_stat:::
--
2.40.0.348.gf938b09366-goog
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