netdev - Re: [PATCH v5] net/mlx5: Reclaim max 50K pages at once

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Date: Tue, 25 Jun 2024 10:30:29 +0530
From: Anand Khoje <anand.a.khoje@...cle.com>
To: Jesse Brandeburg <jesse.brandeburg@...el.com>, linux-rdma@...r.kernel.org,
        linux-kernel@...r.kernel.org, netdev@...r.kernel.org
Cc: saeedm@...lanox.com, leon@...nel.org, tariqt@...dia.com,
        edumazet@...gle.com, kuba@...nel.org, pabeni@...hat.com,
        davem@...emloft.net
Subject: Re: [PATCH v5] net/mlx5: Reclaim max 50K pages at once

On 6/25/24 02:11, Jesse Brandeburg wrote:
> On 6/24/2024 8:33 AM, Anand Khoje wrote:
>
>> --- a/drivers/net/ethernet/mellanox/mlx5/core/pagealloc.c
>> +++ b/drivers/net/ethernet/mellanox/mlx5/core/pagealloc.c
>> @@ -608,6 +608,7 @@ enum {
>>   	RELEASE_ALL_PAGES_MASK = 0x4000,
>>   };
>>   
>> +#define MAX_RECLAIM_NPAGES -50000
> Can you please explain why this is negative? There doesn't seem to be
> any reason mentioned in the commit message or code.
>
> At the very least it's super confusing to have a MAX be negative, and at
> worst it's a bug. I don't have any other context on this code besides
> this patch, so an explanation would be helpful.
>
>
>
Hi Jesse,

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.

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.

I hope that explains.

Thanks,

Anand