linux-kernel - Re: rhashtable: Use __vmalloc with GFP

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Message-ID: <20151209024248.GA20213@pox.localdomain>
Date:	Wed, 9 Dec 2015 03:42:48 +0100
From:	Thomas Graf <tgraf@...g.ch>
To:	Herbert Xu <herbert@...dor.apana.org.au>
Cc:	David Miller <davem@...emloft.net>, Phil Sutter <phil@....cc>,
	Eric Dumazet <eric.dumazet@...il.com>, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org, fengguang.wu@...el.com,
	wfg@...ux.intel.com, lkp@...org
Subject: Re: rhashtable: Use __vmalloc with GFP_ATOMIC for table allocation

On 12/09/15 at 10:38am, Herbert Xu wrote:
> On Wed, Dec 09, 2015 at 03:36:32AM +0100, Thomas Graf wrote:
> > 
> > Without knowing your exact implementation plans: introducing an
> > additional reference indirection for every lookup will have a
> > huge performance penalty as well.
> > 
> > Is your plan to only introduce the master table after an
> > allocation has failed?
> 
> Right, obviously the extra indirections would only come into play
> after a failed allocation.  As soon as we can run the worker thread
> it'll try to remove the extra indirections by doing vmalloc.

OK, this sounds like a good compromise. The penalty is isolated
for the duration of the atomic burst.
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