On to, 28 tammi 2021, Chris Murphy wrote:
>> > ram + zram + in-memory-zwap in the check.
>>
>> For bare metal IPA uses the python3-psutil call:
>> psutil.virtual_memory.available()
>>
>> I don't know how/if psutil reports zram (or cgroup v1 and v2 for that
>> matter).
>
> psutil (in general) reports data from /proc/meminfo; available come
> from MemAvailable: in that file. This is defined in kernel as:
>
>MemAvailable: An estimate of how much memory is available for starting new
> applications, without swapping. Calculated from MemFree,
> SReclaimable, the size of the file LRU lists, and the low
> watermarks in each zone.
> The estimate takes into account that the system needs some
> page cache to function well, and that not all reclaimable
> slab will be reclaimable, due to items being in use. The
> impact of those factors will vary from system to system.
>
>Notice "without swapping" in second line. Next question, how zram impacts
>reporting of MemAvailable by kernel?
This is a good note. If zram breaks kernel API promise to user space
(/proc/meminfo is one such API), how can it be enabled by default. I
also would question enabling zram by default if it does not play along
with cgroups. We do depend on cgroups being properly managed by systemd,
including resource allocation.
In my opinion, zram enablement in Fedora is quite premature.
It's the default Fedora wide since Fedora 33. It's been used by default in
Fedora IoT since the beginning, and in openQA Anaconda tests for even
longer than that.
What's premature about it?
I tried to point to my line of thought in the sentence above you quoted.
You might think that is irrelevant which thought I'd accept as an
argument and we can agree to disagree.
Back to this subthread's topic. Looks like Adam found that something
did reduce a memory available to the system after standard install process
between Jan 24th and Jan 27th. Something did allocate ~120MB of RAM more
than it did previously on Fedora Server but also the kernel reports
~600MB less RAM available even though in both cases QEMU was configured
with 2048MB RAM.
--
/ Alexander Bokovoy
Sr. Principal Software Engineer
Security / Identity Management Engineering
Red Hat Limited, Finland
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