netdev - Re: After memory pressure: can't read from tape anymore

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [day] [month] [year] [list]

Message-ID: <4D08EC7E.5080201@vlnb.net>
Date:	Wed, 15 Dec 2010 19:27:42 +0300
From:	Vladislav Bolkhovitin <vst@...b.net>
To:	Stephen Hemminger <shemminger@...tta.com>
CC:	James Bottomley <James.Bottomley@...e.de>,
	Lukas Kolbe <lkolbe@...hfak.uni-bielefeld.de>,
	Kai Mäkisara <kai.makisara@...umbus.fi>,
	FUJITA Tomonori <fujita.tomonori@....ntt.co.jp>,
	linux-scsi@...r.kernel.org, Kashyap Desai <Kashyap.Desai@....com>,
	netdev@...r.kernel.org
Subject: Re: After memory pressure: can't read from tape anymore

Stephen Hemminger, on 12/15/2010 01:23 AM wrote:
> On Tue, 14 Dec 2010 23:35:37 +0300
> Vladislav Bolkhovitin <vst@...b.net> 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



--
To unsubscribe from this list: send the line "unsubscribe netdev" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html