From mboxrd@z Thu Jan 1 00:00:00 1970 From: Vladislav Bolkhovitin Subject: Re: After memory pressure: can't read from tape anymore Date: Wed, 15 Dec 2010 19:27:42 +0300 Message-ID: <4D08EC7E.5080201@vlnb.net> References: <1290971729.2814.13.camel@larosa> <20101203212453W.fujita.tomonori@lab.ntt.co.jp> <4CF905D1.6050903@kolumbus.fi> <1291388776.2881.4.camel@mulgrave.site> <1291395815.2814.376.camel@larosa> <1291399814.2881.66.camel@mulgrave.site> <4D07D519.70800@vlnb.net> <20101214142320.27d911d5@nehalam> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Cc: James Bottomley , Lukas Kolbe , =?ISO-8859-1?Q?Kai_M=E4kisara?= , FUJITA Tomonori , linux-scsi@vger.kernel.org, Kashyap Desai , netdev@vger.kernel.org To: Stephen Hemminger Return-path: In-Reply-To: <20101214142320.27d911d5@nehalam> Sender: linux-scsi-owner@vger.kernel.org List-Id: netdev.vger.kernel.org Stephen Hemminger, on 12/15/2010 01:23 AM wrote: > On Tue, 14 Dec 2010 23:35:37 +0300 > Vladislav Bolkhovitin wrote: > >> What is interesting to me in this regard is how networking with 9K jumbo >> frames manages to work acceptably reliable? Jumbo frames used >> sufficiently often, including under high memory pressure. >> >> I'm not a deep networking guru, but network drivers need to allocate >> physically continual memory for skbs, which means 16K per 9K packet, >> which means order 2 allocations per skb. > > Good network drivers support fragmentation and allocate a small portion > for the header and allocate pages for the rest. This requires no higher > order allocation. The networking stack takes fragmented data coming > in and does the necessary copy/merging to access contiguous headers. > > There are still some crap network drivers that require large contiguous > allocation. These should not be used with jumbo frames in real > environments. I see. Thanks for clarifying it. Vlad