A regression caused by #10636 (released in 7.0.1) causes Redis startup warning about overcommit to be missing when needed and printed when not.
Also, using atoi() to convert the string's value to an integer cannot discern
between an actual 0 (zero) having been read, or a conversion error.
When `/proc/sys/vm/overcommit_memory` is inaccessible, fp is NULL.
`checkOvercommit` will return -1 without setting err_msg, and then
the err_msg is used to print the log, crash the server.
Set the err_msg variables to Null when declaring it, seems safer.
And the overcommit_memory error log will print two "WARNING",
like `WARNING WARNING overcommit_memory is set to 0!`, this PR
also removes the second WARNING in `checkOvercommit`.
Reported in #10846. Fixes#10846. Introduced in #10636 (7.0.1)
This PR does 2 main things:
1) Add warning for suspected slow system clocksource setting. This is Linux specific.
2) Add a `--check-system` argument to redis which runs all system checks and prints a report.
## System checks
Add a command line option `--check-system` which runs all known system checks and provides
a report to stdout of which systems checks have failed with details on how to reconfigure the
system for optimized redis performance.
The `--system-check` mode exists with an appropriate error code after running all the checks.
## Slow clocksource details
We check the system's clocksource performance by running `clock_gettime()` in a loop and then
checking how much time was spent in a system call (via `getrusage()`). If we spend more than
10% of the time in the kernel then we print a warning. I verified that using the slow clock sources:
`acpi_pm` (~90% in the kernel on my laptop) and `xen` (~30% in the kernel on an ec2 `m4.large`)
we get this warning.
The check runs 5 system ticks so we can detect time spent in kernel at 20% jumps (0%,20%,40%...).
Anything more accurate will require the test to run longer. Typically 5 ticks are 50ms. This means
running the test on startup will delay startup by 50ms. To avoid this we make sure the test is only
executed in the `--check-system` mode.
For a quick startup check, we specifically warn if the we see the system is using the `xen` clocksource
which we know has bad performance and isn't recommended (at least on ec2). In such a case the
user should manually rung redis with `--check-system` to force the slower clocksource test described
above.
## Other changes in the PR
* All the system checks are now implemented as functions in _syscheck.c_.
They are implemented using a standard interface (see details in _syscheck.c_).
To do this I moved the checking functions `linuxOvercommitMemoryValue()`,
`THPIsEnabled()`, `linuxMadvFreeForkBugCheck()` out of _server.c_ and _latency.c_
and into the new _syscheck.c_. When moving these functions I made sure they don't
depend on other functionality provided in _server.c_ and made them use a standard
"check functions" interface. Specifically:
* I removed all logging out of `linuxMadvFreeForkBugCheck()`. In case there's some
unexpected error during the check aborts as before, but without any logging.
It returns an error code 0 meaning the check didn't not complete.
* All these functions now return 1 on success, -1 on failure, 0 in case the check itself
cannot be completed.
* The `linuxMadvFreeForkBugCheck()` function now internally calls `exit()` and not
`exitFromChild()` because the latter is only available in _server.c_ and I wanted to
remove that dependency. This isn't an because we don't need to worry about the
child process created by the test doing anything related to the rdb/aof files which
is why `exitFromChild()` was created.
* This also fixes parsing of other /proc/\<pid\>/stat fields to correctly handle spaces
in the process name and be more robust in general. Not that before this fix the rss
info in `INFO memory` was corrupt in case of spaces in the process name. To
recreate just rename `redis-server` to `redis server`, start it, and run `INFO memory`.
