RE: [PATCH] config: limit lcore variable maximum size to 4k

["Morten Brørup" <mb@smartsharesystems.com>]

> From: Morten Brørup [mailto:mb@smartsharesystems.com]
> Sent: Friday, 8 November 2024 19.35
> 
> > From: David Marchand [mailto:david.marchand@redhat.com]
> > Sent: Friday, 8 November 2024 19.18
> >
> > OVS locks all pages to avoid page faults while processing packets.

It sounds smart, so I just took a look at how it does this. I'm not sure, but it seems like it only locks pages that are actually mapped (current and future).

> > 1M for each lcore translates to allocating 128M with default build
> > options on x86.
> > This resulted in OOM while running unit tests in parallel.

Is the root cause the lcore variables library itself, or the unit test using a lot of memory for testing the lcore variables?
We don't want to fix the library if the problem is elsewhere.

> >
> > At the moment, the more demanding DPDK user of lcore variable is
> > rte_service, with a 2112 bytes object.
> >
> > Limit the lcore variable maximum size to 4k which looks more
> > reasonable.
> 
> 4 KB is not future proof.
> 
> Here's an example where 16 KB is cutting it close:
> https://inbox.dpdk.org/dev/98CBD80474FA8B44BF855DF32C47DC35E9F7D0@smart
> server.smartshare.dk/
> 
> Depends on how we are going to use it. 4 KB suffices if we only want to
> use it for "small" structures.
> 
> Would 64 KB work as a compromise?