Subject: Re: [ath9k-devel] [PATCH 1/3] ath9k: Decrease skb size to fit into
 one page.
From: Eric Dumazet <eric.dumazet@gmail.com>
To: "Luis R. Rodriguez" <lrodriguez@atheros.com>
Cc: Ben Greear <greearb@candelatech.com>,
	Johannes Berg <johannes@sipsolutions.net>,
	"ath9k-devel@venema.h4ckr.net" <ath9k-devel@venema.h4ckr.net>,
	"linux-wireless@vger.kernel.org" <linux-wireless@vger.kernel.org>
In-Reply-To: <20110107200913.GF21588@tux>
References: <1294361165-15308-1-git-send-email-greearb@candelatech.com>
	 <1294397880.3467.1.camel@jlt3.sipsolutions.net>
	 <4D275CCC.90905@candelatech.com>  <20110107200913.GF21588@tux>
Content-Type: text/plain; charset="UTF-8"
Date: Fri, 07 Jan 2011 21:26:58 +0100
Message-ID: <1294432018.2709.2.camel@edumazet-laptop>
Mime-Version: 1.0
Sender: linux-wireless-owner@vger.kernel.org

Le vendredi 07 janvier 2011 à 12:09 -0800, Luis R. Rodriguez a écrit :
> On Fri, Jan 07, 2011 at 10:34:52AM -0800, Ben Greear wrote:
> > On 01/07/2011 02:58 AM, Johannes Berg wrote:
> > > On Thu, 2011-01-06 at 16:46 -0800, greearb@candelatech.com wrote:
> > >> From: Ben Greear<greearb@candelatech.com>
> > >>
> > >> Patch is from Eric Dumazet, as described here:
> > >> https://patchwork.kernel.org/patch/104271/
> > >>
> > >> Reported-by: Michael Guntsche<mike@it-loops.com>
> > >> Signed-off-by: Eric Dumazet<eric.dumazet@gmail.com>
> > >> Signed-off-by: Ben Greear<greearb@candelatech.com>
> > >> ---
> > >>
> > >> NOTE:  This needs review by ath9k and/or other informed
> > >> people.
> > >
> > > This doesn't make sense. It might help, but it'll probably lead to not
> > > being able to receive all frames off the air.
> > >
> > > If this is an issue, ath9k should do paged RX like iwlwifi.
> > 
> > Ok, I backed this out..but now I'm back to getting buffer allocation
> > failures (and this is on a system with 2GB RAM).
> > 
> > Seems it's coming from mac80211 instead of ath9k, at least most of
> > the time (I'm using 60 stations, so it probably needs to make lots of
> > copies in the rx path).  The traffic I'm generating/receiving is 1024 byte UDP
> > payloads.
> > 
> > Does this mean I really received a packet that was 3872 bytes long,
> > or is the skb_copy allocating/copying empty data?
> 
> Good question. The buffer we setup for DMA should be large since we
> need to support AMSDU RX up to a certain bytes of RX data for the frame.
> Harwdware should tell us the right size for the RX'd data and the skb
> should be set with that size, respectively. Following this logic,
> skb_copy() should only allocate on the order of the required skb->len.
> 
> Remember that trick we did to force the older memory leak issues by
> forcing an skb_copy() on every RX'd frame and then just discarding that
> buffer immediately? You can try to do the same and print the skb->len
> there, just to check what's going on.


Using skb_copy() is wrong then, since it makes a copy (order-1
allocations)

It should use :
 skb_alloc( actual_size_of_frame  not the 3840 thing ...)
 copy(data)