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Bug 2228949 - The `sar -B` reports '%vmeff' beyond 100
Summary: The `sar -B` reports '%vmeff' beyond 100
Keywords:
Status: CLOSED MIGRATED
Alias: None
Product: Red Hat Enterprise Linux 8
Classification: Red Hat
Component: sysstat
Version: ---
Hardware: Unspecified
OS: Unspecified
unspecified
low
Target Milestone: rc
: ---
Assignee: Lukáš Zaoral
QA Contact: qe-baseos-daemons
Šárka Jana
URL:
Whiteboard:
Depends On:
Blocks:
TreeView+ depends on / blocked
 
Reported: 2023-08-03 17:41 UTC by Abdul Rehman Quadri
Modified: 2023-10-06 16:36 UTC (History)
3 users (show)

Fixed In Version:
Doc Type: Known Issue
Doc Text:
.The `%vmeff` metric from the `sysstat` package displays incorrect values The `sysstat` package provides the `%vmeff` metric to measure the page reclaim efficiency. The values of the `%vmeff` column returned by the `sar -B` command are incorrect because `sysstat` does not parse all relevant `/proc/vmstat` values provided by later kernel versions. To work around this problem, you can calculate the `%vmeff` value manually from the `/proc/vmstat` file. For details, see link:https://access.redhat.com/solutions/7027076[Why the `sar(1)` tool reports `%vmeff` values beyond 100 % in RHEL 8 and RHEL 9?]
Clone Of:
Environment:
Last Closed: 2023-10-06 16:36:09 UTC
Type: Bug
Target Upstream Version:
Embargoed:

Attachments (Terms of Use)


Links
System ID Private Priority Status Summary Last Updated
Github sysstat/sysstat/commit/7a78deaab97687bda9ca4bfb3eb98ceba2f87343 0 None None None 2023-08-21 12:28:36 UTC
Github sysstat/sysstat/commit/a8e71abf2a4f953da2c0a212a7f3281f285f7e74 0 None None None 2023-08-21 13:13:32 UTC
Github sysstat/sysstat/commit/c52e38145bedb9ab6c352c2e60e04fdb6607b046 0 None None None 2023-08-21 12:58:50 UTC
Red Hat Issue Tracker   RHEL-12008 0 None Migrated None 2023-10-06 16:57:59 UTC
Red Hat Issue Tracker RHELPLAN-164421 0 None None None 2023-08-03 17:41:55 UTC
Red Hat Knowledge Base (Solution) 7027076 0 None None None 2023-08-08 17:18:59 UTC

Description Abdul Rehman Quadri 2023-08-03 17:41:36 UTC 
Description:
The `sar -B` commands report the paging statistics where the output
includes '%vmeff' column.
The `%vmeff` as per the man page is [pgsteal / pgscan].
 
However, the sysstat package shipped with RHEL 8 is reporting the '%vmeff'
value beyond 100. It appears the number of pages being stolen is getting
high from the number of pages scanned causing the percentage to go beyond 100.
 
 
Version-Release number of selected component (if applicable):
sysstat-11.7.3
 
 
How reproducible:
Always
 
 
Steps to Reproduce:
1. Stress the system for memory utilization so that the cache is reclaimed & swapping occurs.
2. sar -B
3. And look for the `%vmeff` column
 
 
Actual results:
# sar -B 1
Linux 4.18.0-477.13.1.el8_8.x86_64 (8rhel)      08/02/2023      _x86_64_        (2 CPU)
 
11:20:59 PM  pgpgin/s pgpgout/s   fault/s  majflt/s  pgfree/s pgscank/s pgscand/s pgsteal/s    %vmeff
 
11:22:33 PM   2392.00  59816.00 267663.00     49.00   7591.00  72128.00 221023.00  13772.00      4.70
11:22:34 PM      0.00  44344.00  10756.00      0.00  11213.00   9747.00  12186.00  21048.00     95.96
11:22:35 PM      0.00  56852.00   4489.00      0.00   6734.00  11552.00   8879.00  12422.00     60.80
11:22:36 PM      0.00 145852.00      0.00      0.00   5919.00  40928.00  33272.00   9052.00     12.20
11:22:37 PM      0.00      0.00      0.00      0.00    451.00      0.00      0.00      0.00      0.00
11:22:38 PM      0.00 107164.71  74018.63      0.00  72985.29  34425.49  60266.67 135484.31    143.08  <<---------------
11:22:39 PM      0.00 661857.43 168127.72      0.00 171582.18 136464.36 273825.74 337794.06     82.33
11:22:40 PM   6345.16 396100.00  97660.48    238.71 101485.48 164530.65 189000.81 199556.45     56.45
11:22:41 PM 221642.11 420126.32 106085.53   8265.79 108259.21 179317.11  33044.74 208792.11     98.32
11:22:42 PM 188316.00 194596.00  50992.00   7308.00  53776.00 121291.00      0.00 100698.00     83.02
11:22:44 PM 126050.60 120689.16  37369.28   4750.00  34137.95 205112.65      0.00  62277.11     30.36
11:22:45 PM 167085.11 156646.81  46920.21   6481.91  42398.94  81422.34      0.00  78972.34     96.99
11:22:46 PM   3776.00    324.00    446.00     77.00   4999.00   4992.00      0.00   9760.00    195.51  <<---------------
11:22:47 PM 101304.00  91288.00  29284.00   4021.00  24876.00  46793.00      0.00  44660.00     95.44
11:22:48 PM  64076.00  57072.00  17995.00   2567.00  15425.00  29758.00      0.00  28138.00     94.56
11:22:49 PM 185700.00 177892.00  51774.00   7266.00  47268.00  91999.00      0.00  89062.00     96.81
11:22:50 PM  20348.00  35032.00   6457.00    734.00   8275.00  16884.00      0.00  15244.00     90.29
11:22:51 PM  52048.00  64032.00  16016.00   1857.00  16275.00  32504.00      0.00  30404.00     93.54
11:22:52 PM 128552.00 118348.00  36891.00   4865.00  33756.00  61833.00      0.00  61324.00     99.18
11:22:53 PM  50684.00  57192.00  15486.00   1878.00  11881.00  25835.00      0.00  21800.00     84.38
11:22:54 PM   1524.00     48.00    273.00     38.00   4130.00   3665.00      0.00   7256.00    197.98  <<---------------
 
 
Expected results:
The value of %vmeff should be <=100%


When the same test is run in RHEL 7 with the same memory & the swappiness value
# sar -B 1
Linux 3.10.0-1160.88.1.el7.x86_64 (7rhel)       08/02/2023      _x86_64_        (2 CPU)
 
11:21:06 PM  pgpgin/s pgpgout/s   fault/s  majflt/s  pgfree/s pgscank/s pgscand/s pgsteal/s    %vmeff
 
11:21:39 PM    714.43 209566.17  51124.38     23.38   1208.96   1022.39    905.47    957.71     49.68
11:21:41 PM    223.33 102963.33  55827.50     20.00  72180.00  71380.83   5201.67  71120.00     92.87
11:21:42 PM    125.00 234335.00  73311.25      6.25  92026.25  88120.00  28610.00  89993.75     77.10
11:21:43 PM      0.00 235892.75  68480.43      0.00  68121.01  31860.87  85258.70  67514.49     57.65
11:21:44 PM     39.67 174941.32  39371.90      1.65  39785.95  17560.33  64147.93  39501.65     48.34
11:21:45 PM    423.81 625538.10 247097.62     38.10 438609.52  85995.24  18441.67  73275.00     70.16
11:21:46 PM    182.61  63239.13  59243.48     18.48  43644.57  46348.91  12268.48  43234.78     73.76
11:21:47 PM   3107.69 327111.54 175599.04    121.15 188900.96 108803.85  55619.23 105988.46     64.46
11:21:48 PM    878.79 260593.94  62313.64    101.52  62625.76  35265.15  80795.45  61692.42     53.16
11:21:49 PM     49.06 237984.91  58366.04     11.32  58866.98  32422.64 117079.25  58439.62     39.09


Additional info:
Something similar was reported on Github:
https://github.com/sysstat/sysstat/issues/343
Comment 6 Lukáš Zaoral 2023-08-21 12:28:36 UTC 
The upstream has decided to remove the %vmeff column altogether with the following explanation in commit https://github.com/sysstat/sysstat/commit/7a78deaab97687bda9ca4bfb3eb98ceba2f87343.

> Remove %vmeff metric displayed by sar -B (paging statistics).
> With recent kernels, this metric was wrongly calculated. Decision was
> made to remove it as it was more a kernel metric than a system one.
Comment 7 Lukáš Zaoral 2023-08-21 12:58:51 UTC 
Relate manual page changes: https://github.com/sysstat/sysstat/commit/c52e38145bedb9ab6c352c2e60e04fdb6607b046
Comment 10 RHEL Program Management 2023-10-06 16:35:47 UTC 
Issue migration from Bugzilla to Jira is in process at this time. This will be the last message in Jira copied from the Bugzilla bug.
Comment 11 RHEL Program Management 2023-10-06 16:36:09 UTC 
This BZ has been automatically migrated to the issues.redhat.com Red Hat Issue Tracker. All future work related to this report will be managed there.

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