From mboxrd@z Thu Jan 1 00:00:00 1970 Message-ID: <42BC1573.90201@engr.sgi.com> Date: Fri, 24 Jun 2005 09:15:15 -0500 From: Ray Bryant MIME-Version: 1.0 Subject: Re: [Lhms-devel] Re: [PATCH 2.6.12-rc5 0/10] mm: manual page migration-rc3 -- overview References: <20050622163908.25515.49944.65860@tomahawk.engr.sgi.com> In-Reply-To: Content-Type: text/plain; charset=us-ascii; format=flowed Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org Return-Path: To: Christoph Lameter Cc: Ray Bryant , Hirokazu Takahashi , Andi Kleen , Dave Hansen , Marcelo Tosatti , Christoph Hellwig , Ray Bryant , linux-mm , lhms-devel@lists.sourceforge.net, Paul Jackson , Nathan Scott List-ID: Christoph Lameter wrote: > > > There is PF_FREEZE flag used by the suspend feature that could > be used here to send the process into the "freezer" first. Using regular > signals to stop a process may cause races with user space code also doing > SIGSTOP SIGCONT on a process while migrating it. > > In general, process flags are only updatable by the current process. There is no locking applied. Having the migrating task set the PF_FREEZE bit in the migrated process runs the risk of losing the update to some other flags bit that is simultaneously set by the (running) migrated process. I suppose this could be fixed as well by introducing a second flags word in the task_struct. But this starts to sound like a reimplemtnation of signals. The other concern (probably not a problem on Altix :-) ), is what happens if a process migration is underway at the time of a suspend. When the resume occurs, all processes will be unfrozen, including the task that is under migration. At the moment, I'm not convinced that this is a better path than depending on SIGSTOP/SIGCONT. It is a resonable restriction that processes eligble for migration are not allowed to use those signals themselves, in particular for the batch environment this is targeted at. -- Best Regards, Ray ----------------------------------------------- Ray Bryant 512-453-9679 (work) 512-507-7807 (cell) raybry@sgi.com raybry@austin.rr.com The box said: "Requires Windows 98 or better", so I installed Linux. ----------------------------------------------- -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: aart@kvack.org