netdev - RE: [net-next PATCH 0/4] net: frag patchset for fixing LRU scalabilityissue

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Date:	Thu, 25 Apr 2013 13:39:55 +0200
From:	Jesper Dangaard Brouer <brouer@...hat.com>
To:	David Laight <David.Laight@...LAB.COM>
Cc:	"David S. Miller" <davem@...emloft.net>,
	Hannes Frederic Sowa <hannes@...essinduktion.org>,
	netdev@...r.kernel.org, Eric Dumazet <eric.dumazet@...il.com>
Subject: RE: [net-next PATCH 0/4] net: frag patchset for fixing LRU
 scalabilityissue

On Wed, 2013-04-24 at 17:21 +0100, David Laight wrote:
> > I have dropped the idea of doing "direct hash cleaning".  Instead I
> > have simply choosen to solve the global LRU list problem, by making
> > the LRU list be per CPU.
> 
> How can a per-cpu LRU list work?
> I see two immediate problems:
> - Ensuring the normal 'allocate' and 'free' are always done
>   on the same cpu (free will need to remove items from any
>   LRU list).
> - Ensuring that there all the items aren't on the LRU lists
>   of other cpus - meaning one can't be allocated.
> 
> The only way this could work is if the allocation limit
> is also per-cpu and you can guarantee that the alloc and
> free for any given item will always happen on the same cpu.
> 
> (alloc as in 'add to LRU list, free as in 'remove from LRU list).

Please read patch-04.

I've added "cpu_alloc" to record the CPU were the first fragment got
allocated.  After which all frags gets accounted to that CPU,
add/remove/timeout etc.

--Jesper




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