netdev - Re: [PATCH 1/5] rhashtable: Remove gfp_flags from insert and remove functions

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Date:	Tue, 23 Sep 2014 21:11:31 -0700
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	Thomas Graf <tgraf@...g.ch>
Cc:	Eric Dumazet <eric.dumazet@...il.com>, davem@...emloft.net,
	paulmck@...ux.vnet.ibm.com, john.r.fastabend@...el.com,
	kaber@...sh.net, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/5] rhashtable: Remove gfp_flags from insert and remove functions

Thomas Graf <tgraf@...g.ch> writes:

> On 09/15/14 at 05:35am, Eric Dumazet wrote:
>> On Mon, 2014-09-15 at 14:18 +0200, Thomas Graf wrote:
>> > As the expansion/shrinking is moved to a worker thread, no allocations
>> > will be performed anymore.
>> > 
>> 
>> You meant : no GFP_ATOMIC allocations ?
>> 
>> I would rephrase using something like :
>> 
>> Because hash resizes are potentially time consuming, they'll be
>> performed in process context where GFP_KERNEL allocations are preferred.
>
> I meant to say no allocations in insert/remove anymore but your wording
> is even clearer. I'll update it.
>
>> > -	tbl = kzalloc(size, flags);
>> > +	tbl = kzalloc(size, GFP_KERNEL);
>> 
>> Add __GFP_NOWARN, as you fallback to vzalloc ?
>
> Good point.

It needs to be both __GFP_NOWARN and __GFP_NORETRY.

Otherwise the system will kick in the OOM killer before it falls back to
vzalloc.  Which I can't imagine anyone wanting.

Look at the history of alloc_fdmem in fs/file.c for the real world
reasoning.

Eric
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