From mboxrd@z Thu Jan 1 00:00:00 1970 Message-ID: <39AA5D41.C59CC2DE@tuke.sk> Date: Mon, 28 Aug 2000 14:38:25 +0200 From: Jan Astalos MIME-Version: 1.0 Subject: Re: Question: memory management and QoS References: <39A4F548.B8EB5308@tuke.sk> <20000828154744.A3741@saw.sw.com.sg> <39AA30AF.14C17C50@tuke.sk> <20000828193032.B5579@saw.sw.com.sg> Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org Return-Path: To: Andrey Savochkin Cc: linux-mm@kvack.org, Yuri Pudgorodsky List-ID: Andrey Savochkin wrote: > > On Mon, Aug 28, 2000 at 11:28:15AM +0200, Jan Astalos wrote: > > Andrey Savochkin wrote: > > > I don't think that personal swapfiles is an efficient approach to achieve > > > QoS. Most of the space will be reserved for exceptional cases, and, thus, > > > wasted, as Yuri has mentioned. A shared swap space allowing exceeding the > > > guaranteed amount (if the memory isn't really used) is much more efficient > > > spending of the space. If the system has some spare memory, users exceeding > > > their limits may still use it (but, certainly, only if only some of them, not > > > all, exceed the limits). Moreover, if some users don't consume all the > > > memory guaranteed to them, others may temporarily use it. > > > > I think I explained my points clearly enough in my second reply to Yuri so I won't > > repeat it again. > > > > I still claim that per user swapfiles will: > > - be _much_ more efficient in the sense of wasting disk space (saving money) > > because it will teach users efficiently use their memory resources (if > > user will waste the space inside it's own disk quota it will be his own > > problem) > > - provide QoS on VM memory allocation to users (will guarantee amount of > > available VM for user) > > - be able to improve _per_user_ performance of system (localizing performance > > problems to users that caused them and reducing disk seek times) > > - shift the problem with OOM from system to user. > > Ok, tell me: if user A has swapfile of 10MB and doesn't use it, whether user > B is allowed to use it meanwhile? > If the answer is no, it's a waste of space, as I said. As a user, you would waste 10MB of your 20MB quota ? I don't think so... > If the answer is yes, I don't buy your argument of better clustering and less > fragmentation. Do you really need to post questions like that ? It's obvious that swapfiles would be protected from access by another users. That's why they will be _personal_. > > >From my point of view, the real topics are > 1. memory QoS, which starts from controlled sharing of in-core memory between > users and, then, sharing of swap space, and the swap storage organization > (per-user or global) being a second-order question because separate > storages may easily be "emulated" by just quotas, and visa versa; How the quotas will give you per user clustered pages ? If the quotas will change who will maintain them, sysadmin ? Look, how much of system maintenance cost is cost of system administration ? Still convinced that quotas on VM are good idea ? > 2. swap-out clusterization. > Speaking about the clusterization, the current code already keeps this aspect > in mind. It may be more or less efficient, but it's a separate topic. ? OK. Your are aimed on management of physical memory. I _is_ important. I'm aimed on VM QoS guaranties. From my point of view this is important too... As I said, MM of physical memory is core of QoS. But without VM QoS there wouldn't be _any_ memory QoS at all. > > > I think that your beancounter is a big step towards good QoS in Linux MM, but > > I'm a bit confused when I'll hear "...users exceeding their limits". What's the > > limit good for if it can be exceeded ? Can you rethought the term ? > > Well, I usually call them "thresholds" rather than "limits". > Users are guaranteed to have some quality of service below the these > thresholds, i.e. that their allocations succeed, that the processes aren't > killed because of OOM, that the pages aren't swapped out. > Over the thresholds the resources are given and requests are served on the > best-effort basis. > > > Can you describe how to avoid VM shortage by beancounter ? > > I don't want to avoid VM shortage. > The goal is to introduce different levels of service and allows > administrators to manage it. excellent. If you'll make it flexible enough to make adding of new MM policy straightforward, you'll have my thanks... > Users obeying their "contracts" (staying below the thresholds set for them) > have some guarantees. The guarantees are real if the administrator ensures > that the sum of guaranteed amounts of resources is not greater than what's > available. > Users disobeying their "contracts" may face negative effects with the chances > depending on the amount of unused resources and the degree of their > violation. > > VM shortage is possible (and total avoiding it is very inefficient). > The goal is to make its consequences controllable, guarantee that certain > processes will never suffer from it etc. I can't resist :-). So you have effectively transformed the _problem_of_VM_shortage_ to the _someone_else's_problem_ putting it completely on the shoulders of sysadmins. Why I have still impression that it's not the right way ? Hmm, maybe because the cost of system administation... Can't you still see how easilly personal swapfiles would solve it ? Regards, Jan -- 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.eu.org/Linux-MM/