linux-kernel - Re: [PATCH net-next 2/3] net: netpoll: Individualize the skb pool

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Message-ID: <20241101-calculating-paper-potoo-beb116@leitao>
Date: Fri, 1 Nov 2024 04:56:14 -0700
From: Breno Leitao <leitao@...ian.org>
To: Jakub Kicinski <kuba@...nel.org>
Cc: horms@...nel.org, davem@...emloft.net, edumazet@...gle.com,
	pabeni@...hat.com, thepacketgeek@...il.com, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org, davej@...emonkey.org.uk,
	vlad.wing@...il.com, max@...sevol.com, kernel-team@...a.com,
	jiri@...nulli.us, jv@...sburgh.net, andy@...yhouse.net,
	aehkn@...hub.one, Rik van Riel <riel@...riel.com>,
	Al Viro <viro@...iv.linux.org.uk>
Subject: Re: [PATCH net-next 2/3] net: netpoll: Individualize the skb pool

On Thu, Oct 31, 2024 at 06:28:57PM -0700, Jakub Kicinski wrote:
> On Fri, 25 Oct 2024 07:20:19 -0700 Breno Leitao wrote:
> > The current implementation of the netpoll system uses a global skb pool,
> > which can lead to inefficient memory usage and waste when targets are
> > disabled or no longer in use.
> > 
> > This can result in a significant amount of memory being unnecessarily
> > allocated and retained, potentially causing performance issues and
> > limiting the availability of resources for other system components.
> > 
> > Modify the netpoll system to assign a skb pool to each target instead of
> > using a global one.
> > 
> > This approach allows for more fine-grained control over memory
> > allocation and deallocation, ensuring that resources are only allocated
> > and retained as needed.
> 
> If memory consumption is a concern then having n pools for n targets
> rather than one seems even worse? 
> 
> Is it not better to flush the pool when last target gets disabled?

That is an option as well, we can create a refcount and flush the pool
when it reaches to zero. This will require some core reoganization due
to the way the buffer are initialized (at early initi), but, totally
doable. In fact, this is how I started this patchset.

On the other side, it seems a better design to have a pool per user, and
they are independent and not sharing the same pool.

In fact, if the pool is per-user, we can make the whole netpoll
transmission faster, just dequeing a skb from the pool instead of trying
to allocate an fresh skb.