From mboxrd@z Thu Jan 1 00:00:00 1970 From: kanoj@google.engr.sgi.com (Kanoj Sarcar) Message-Id: <200001132148.NAA32035@google.engr.sgi.com> Subject: Re: [RFC] 2.3.39 zone balancing Date: Thu, 13 Jan 2000 13:48:29 -0800 (PST) In-Reply-To: from "Benjamin C.R. LaHaise" at Jan 13, 2000 04:34:15 PM MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org Return-Path: To: "Benjamin C.R. LaHaise" Cc: Andrea Arcangeli , Rik van Riel , torvalds@transmeta.com, mingo@chiara.csoma.elte.hu, alan@lxorguk.ukuu.org.uk, linux-mm@kvack.org, linux-kernel@vger.rutgers.edu List-ID: > > On Thu, 13 Jan 2000, Kanoj Sarcar wrote: > > > No, I am referring to a different problem that I mentioned in the > > doc. If you have a large number of free regular pages, and the dma > > zone is completely exhausted, the 2.2 decision of balacing the dma > > zone might never fetch an "yes" answer, because it is based on total > > number of free pages, not also the per zone free pages. Right? Things > > will get worse the more non-dma pages there are. > > Kanoj, you're wrong. 2.2 works quite well because of the fact that the > low memory mark will tend to consist almost entirely of DMAable pages. > The only allocations that regularly eat into them on a loaded machine are > interrupts, which tend to be short term allocations anyways. But as soon > as DMAable memory is freed, it tends not to be allocated until interrupts > consume all memory again. Okay, you are telling me what _mostly_ happens, the problem I have pointed out is one that can _probably_ happen under the right conditions of temperature and pressure. Its a good idea to design against boundary conditions, and then improve the design ... > > > Oh, okay I see. There is nothing about the dma zone then, you could > > make the balancing more aggressive for the other zones too. Basically, > > these kinds of tuning should be controlled by sysctls (instead of > > >>7, do >> N), so while most sites will prefer to run with the least > > aggressive balancing, there may be sites with drivers that need > > many high-order pages, they would be willing to sacrifice some > > performance by doing more aggressive balancing. Comes under finetuning > > in the doc. > > Whoa, hold on here. Last time we tried to do more aggresive balancing, it > was a complete and total disaster that resulted in completely random swap > storms, resulting in spectacularly unusable systems on the lower end > (iirc 64mb was around the breakeven point). Before harder limits are > placed on memory types and orders, the behaviour of both kswapd and the > allocator need to be tweaked. so put in the mechanism, but don't start > enforcing it too aggresively. Absolutely. I am _not_ suggesting doing anything much different than in 2.2. All I am saying is that we can provide sysctls (with their default values to mimic 2.2 behavior), then individual developers can tweak those and do performance experiments. Kanoj > > -ben > > -- > 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.nl.linux.org/Linux-MM/ > -- 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.nl.linux.org/Linux-MM/