RE: [PATCH v5] net/mlx5: Reclaim max 50K pages at once

David Laight
2024-06-28T15:44:55Z

...
> The way Mellanox ConnectX5 driver handles 'release of allocated pages
> from HCA' or 'allocation of pages to HCA', is by sending an event to the
> host. This event will have number of pages in it. If the number is
> positive, that indicates HCA is requesting that number of pages to be
> allocated. And if that number is negative, it is the HCA indicating that
> that number of pages can be reclaimed by the host.

A one line comment would do.
Possibly even negating the be32toh() result?

> In this patch we are restricting the maximum number of pages that can be
> reclaimed to be 50000 (effectively this would be -50000 as it is
> reclaim). This limit is based on the capability of the firmware as it
> cannot release more than 50000 back to the host in one go.

Hang on, why are you soft limiting it to the hard limit?
I thought the problem was that releasing a lot of pages took a long
time and 'stuffed' other time-critical tasks.

The only way to resolve that would seem to be to defer the actual freeing
to a low (or at least normal user) priority thread.
You would definitely want to get out of 'softint' context.
(Which is out of napi unless forced to be threaded - and that only really
works if you force the threads under the RT scheduler.)

David

-
Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
Registration No: 1397386 (Wales)