Re: [[RFC][PATCH] v1 0/2] malloc/realloc with transparent huge page support

[Florian Weimer <fw@deneb.enyo.de>]

* Norbert Manthey:

> I have seen [madvise] as the default for different Ubuntu versions
> (16.04, 18.04 and 20.04), so I expect it to be around for at least the
> next 5 years.

Still, it is easier to change a run-time kernel setting than to
upgrade glibc.

>> In the paper, you say this:
>>
>> | Because there might be applications running on the host that would
>> | suffer from larger pages, THP is usually disabled on physical
>> | systems and it is not advised to set the value to always.
>>
>> However, the default value for Red Hat Enterprise Linux 7 is, in fact,
>> "always", so it is puzzling why you see such a large benefit for
>> long-running processes.
>
> All used test systems have not been using [always], but [madvise]. For
> systems that already use [always], I expect the benefit to be much
> smaller. With the 2M alignment, there should be less 4K pages required,
> but we did not really measure the effect of only using the alignment.

I suggest to repeat the experiment with "always".  There is a reason
why this setting exists.  The results presented so far are incomplete.

The paper doesn't provide details on the NUMA configuration of the
test system, so one has to wonder if there are any surprises there as
well.