From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Michael S. Tsirkin" Subject: Re: [PATCH net-next] net: netdev_alloc_skb() use build_skb() Date: Mon, 4 Jun 2012 22:56:42 +0300 Message-ID: <20120604195642.GA2069@redhat.com> References: <1337276056.3403.37.camel@edumazet-glaptop> <20120604123738.GA28992@redhat.com> <1338815213.2760.1806.camel@edumazet-glaptop> <20120604134138.GA29814@redhat.com> <1338818501.2760.1821.camel@edumazet-glaptop> <20120604141731.GA30226@redhat.com> <1338822064.2760.1834.camel@edumazet-glaptop> <20120604181623.GF32205@redhat.com> <1338838185.2760.1899.camel@edumazet-glaptop> <20120604194330.GA1648@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Willy Tarreau , David Miller , netdev@vger.kernel.org To: Eric Dumazet Return-path: Received: from mx1.redhat.com ([209.132.183.28]:10871 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752568Ab2FDT5G (ORCPT ); Mon, 4 Jun 2012 15:57:06 -0400 Content-Disposition: inline In-Reply-To: <20120604194330.GA1648@redhat.com> Sender: netdev-owner@vger.kernel.org List-ID: On Mon, Jun 04, 2012 at 10:43:30PM +0300, Michael S. Tsirkin wrote: > On Mon, Jun 04, 2012 at 09:29:45PM +0200, Eric Dumazet wrote: > > On Mon, 2012-06-04 at 21:16 +0300, Michael S. Tsirkin wrote: > > > > > Yes but if a tcp socket then hangs on, on one of the fragments, > > > while the other has been freed, the whole page is still > > > never reused, right? > > > > > > Doesn't this mean truesize should be 4K? > > > > > > > Yes, or more exactly PAGE_SIZE, but then performance would really go > > down on machines with 64KB pages. > > Maybe we should make the whole frag > > head idea enabled only for PAGE_SIZE=4096. > > > > Not sure we want to track precise truesize, as the minimum truesize is > > SKB_DATA_ALIGN(length + NET_SKB_PAD) + SKB_DATA_ALIGN(sizeof(struct > > skb_shared_info)) (64 + 64 + 320) = 448 > > > > Its not like buggy drivers that used truesize = length > > > > > > Interesting. But where's the threshold? And just to explain why I'm asking, if it's OK to declare 2K when you use 4K, we can do (effectively): + skb->truesize += PAGE_SIZE * nfrags; - skb->truesize += min(1500, skb->data_len); which means with 1500 byte packets we can use as much memory as we did before 4b727361f0bc7ee7378298941066d8aa15023ffb > -- > MST