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

["Mattias Rönnblom" <hofors@lysator.liu.se>]

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?