Date: Wed, 18 Sep 2002 16:15:54 +0200 From: pzw@aabc.dk To: mjohnston@skyweb.ca Cc: isp@freebsd.org Subject: SV: Inactive memory in FreeBSD Message-ID: <E01A200E2339D311AF7E00508B319A2B04C84714@expers.aabc.dk>
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While this is a fine and dandy idea, I have experienced a serious downgrade in response time for some of my websites, when the system has converted all free memory to inactive memory. After a reboot, there was no problem with response time. I've read the article about the VM design, and it is like you say, but, the overhead on memory allocation from inactive memory, instead of free memory, must be very high, that's the only way to explain the situation above. Oh, I'm also stuck with Outlook, so please excuse me for formatting this letter. At least it's not in HTML... Best Regards, Peter ------------------------------------ The VM discussion at http://www.freebsd.org/doc/en_US.ISO8859-1/articles/vm-design/x78.html is enlightening. From what I gather, an inactive page is not a program "hogging up" memory, and there's no need to worry about freeing it. To summarize, pages marked Inact and Cache are similar in that they are candidates to be reused; the difference is that Inact pages are "dirty", i.e. they still have data to be flushed to disk. When there are too many dirty pages, the system will flush them to disk and move them to the Cache queue. Pages in Cache are like free memory, but better. :) Their data is already on disk, so the pages can be instantly reused as free memory if needed, but if the original program tries to access the data again, the page can be revived without having to swap the data back in from disk. An Inact page can be reused, too, but its data has to be flushed first. The VM algorithm controlling when Inact pages are flushed, etc., is magic too deep for me, but judging by the page, the heavier the load, the more aggressively the memory system works. I'm not one to argue re whether FreeBSD is suitable for workstations vs servers, but this particular criterion isn't the one that should make the decision for you. Sorry if the formatting on this comes through broken - I've tried to keep it sane, but I'm stuck with Outlook and it's very sneaky about breaking things. Mark pzw@aabc.dk wrote: > Well, yes, it might be a good thing when you have a lot of reoccurring > tasks, and plenty of memory. > > However, when you compile a program or FTP a file to the server, the chances > of you doing that over and over again is almost null, therefore caching > these processes are a total waste. > > So, FreeBSD is best used for a server system, where you have more RAM than > you use for all normal activity, and to prevent some seldom used tasks to > hog up memory, you should reboot often. > > As a workstation system, you're better of using Windows or Linux, unless > ofc. You're a secretary using the same word processor program day in and day > out. > > IMHO it would be a far better solution, for you to be able to specify the > maximum amount of memory that a program could hog up, so you don't have to > reboot all the time to free memory. > > Best Regards, > Peter > > > > >This is how the vm subsystem is supposed to work. This is normal, this > >is good. Inactive memory is memory that currently has data (programs) > >stored in it, but that data is not currently being used (the programs > >are not currently running). If the data that is currently stored in the > >inactive memory is needed again (you run a program again), you don't have > >to load it off the hard drive. > > >This is a good thing. You don't want to change this. > > >The comparison to solaris is irrelevant, as they (solaris and FreeBSD) have > >different vm subsystems. > > >-- > >Jeremy Faulkner http://www.gldis.ca > > To Unsubscribe: send mail to majordomo@FreeBSD.org > with "unsubscribe freebsd-isp" in the body of the message To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-isp" in the body of the message To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-isp" in the body of the message
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