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

[Thomas Monjalon <thomas@monjalon.net>]

08/11/2024 23:34, Mattias Rönnblom:
> On 2024-11-08 23:13, Thomas Monjalon wrote:
> > 08/11/2024 20:53, Morten Brørup:
> >>> 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.
> > 
> > The fix works for our urgent issue and we want to make a release candidate soon.
> > 
> > 
> >>>> 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.
> > 
> > This is what is stated in the doc:
> > "Lcore variables are suitable for small objects"
> > "The amount of data kept in lcore variables is projected to be small"
> > >>> Would 64 KB work as a compromise?
> > 
> > Let's consider based on the need.
> > The lcore variables are new and we don't want it to degrade the DPDK footprint,
> > at least not in this first version.
> > 4 KB is a memory page on common systems,
> > it looks reasonnable and big enough for a "variable".
> > 
> > Applied, thanks.
> 
> Why do you have maintainers if you just ignore them?

I didn't receive your replies when I started to write this.
Please be comprehensive.
We are in a hurry to stabilize this before the release candidate which is already late.

I'll change to 128 KB as you recommend before pushing to the repository.

PS: maybe I should not have merged this feature in 24.11.