From mboxrd@z Thu Jan 1 00:00:00 1970 From: Arjan van de Ven Subject: Re: [RFC][PATCH 0/3] TCP/IP Critical socket communication mechanism Date: Thu, 15 Dec 2005 09:35:20 +0100 Message-ID: <1134635721.16486.7.camel@laptopd505.fenrus.org> References: <20051215033937.GC11856@waste.org> <20051214.203023.129054759.davem@davemloft.net> <20051215.002120.133621586.davem@davemloft.net> Mime-Version: 1.0 Content-Type: text/plain Content-Transfer-Encoding: 7bit Cc: sri@us.ibm.com, mpm@selenic.com, ak@suse.de, linux-kernel@vger.kernel.org, netdev@vger.kernel.org Return-path: To: "David S. Miller" In-Reply-To: <20051215.002120.133621586.davem@davemloft.net> Sender: linux-kernel-owner@vger.kernel.org List-Id: netdev.vger.kernel.org On Thu, 2005-12-15 at 00:21 -0800, David S. Miller wrote: > From: Sridhar Samudrala > Date: Wed, 14 Dec 2005 23:37:37 -0800 (PST) > > > Instead, you seem to be suggesting in_emergency to be set dynamically > > when we are about to run out of ATOMIC memory. Is this right? > > Not when we run out, but rather when we reach some low water mark, the > "critical sockets" would still use GFP_ATOMIC memory but only > "critical sockets" would be allowed to do so. > > But even this has faults, consider the IPSEC scenerio I mentioned, and > this applies to any kind of encapsulation actually, even simple > tunneling examples can be concocted which make the "critical socket" > idea fail. > > The knee jerk reaction is "mark IPSEC's sockets critical, and mark the > tunneling allocations critical, and... and..." well you have > GFP_ATOMIC then my friend. > > In short, these "seperate page pool" and "critical socket" ideas do > not work and we need a different solution, I'm sorry folks spent so > much time on them, but they are heavily flawed. maybe it should be approached from the other side; having a way to mark connections as low priority (say incoming http connections to your webserver) or as non-critical/expendable would give the "normal" GFP_ATOMIC ones a better chance in case of overload/DDOS etc. It's not going to solve the VM deadlock issue wrt iscsi/nfs; however it might be useful in the "survive slashdot" sense...