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From: Rusty Russell <rusty@rustcorp.com.au>
Subject: Re: virtio ring cleanups, which save stack on older gcc
In-Reply-To: <20140529074117.GI10092@bbox>
References: <87oayh6s3s.fsf@rustcorp.com.au> <1401348405-18614-1-git-send-email-rusty@rustcorp.com.au> <20140529074117.GI10092@bbox>
Date: Thu, 29 May 2014 20:38:33 +0930
Message-ID: <87fvjs7sge.fsf@rustcorp.com.au>
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Sender: owner-linux-mm@kvack.org
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To: Minchan Kim <minchan@kernel.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>, Dave Chinner <david@fromorbit.com>, Jens Axboe <axboe@kernel.dk>, Linux Kernel Mailing List <linux-kernel@vger.kernel.org>, Andrew Morton <akpm@linux-foundation.org>, linux-mm <linux-mm@kvack.org>, "H. Peter Anvin" <hpa@zytor.com>, Ingo Molnar <mingo@kernel.org>, Peter Zijlstra <a.p.zijlstra@chello.nl>, Mel Gorman <mgorman@suse.de>, Rik van Riel <riel@redhat.com>, Johannes Weiner <hannes@cmpxchg.org>, Hugh Dickins <hughd@google.com>, "Michael S. Tsirkin" <mst@redhat.com>, Dave Hansen <dave.hansen@intel.com>, Steven Rostedt <rostedt@goodmis.org>

Minchan Kim <minchan@kernel.org> writes:
> Hello Rusty,
>
> On Thu, May 29, 2014 at 04:56:41PM +0930, Rusty Russell wrote:
>> They don't make much difference: the easier fix is use gcc 4.8
>> which drops stack required across virtio block's virtio_queue_rq
>> down to that kmalloc in virtio_ring from 528 to 392 bytes.
>> 
>> Still, these (*lightly tested*) patches reduce to 432 bytes,
>> even for gcc 4.6.4.  Posted here FYI.
>
> I am testing with below which was hack for Dave's idea so don't have
> a machine to test your patches until tomorrow.
> So, I will queue your patches into testing machine tomorrow morning.

More interesting would be updating your compiler to 4.8, I think.
Saving <100 bytes on virtio is not going to save you, right?

Cheers,
Rusty.

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