Date: Tue, 08 Feb 2005 17:13:19 -0500 From: Chuck Swiger <cswiger@mac.com> To: Pat Maddox <pergesu@gmail.com> Cc: freebsd-questions@freebsd.org Subject: Re: Inactive memory Message-ID: <4209397F.6010204@mac.com> In-Reply-To: <810a540e050208134479b4e774@mail.gmail.com> References: <810a540e050208133310333144@mail.gmail.com> <20050208213612.GA29063@falcon.midgard.homeip.net> <810a540e050208134479b4e774@mail.gmail.com>
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Pat Maddox wrote: > Alright, that lets me know that it's not an entirely bad thing. It > does say, however, that it's fine as long as the free memory isn't > REALLY low. It did get down to 13MB though, as I said. Really low means less than 1 MB. That would indicate the VM system is under so much pressure that it can't maintain the minimum amount of free space it wants to have: vm.v_free_min: 378 vm.v_free_target: 1655 vm.v_free_reserved: 143 vm.v_pageout_free_min: 34 vm.v_free_severe: 260 These numbers are likely to be in 4K pages, 260 * 4K = 1040K ~= 1 MB, and will vary slighty depending on available physical RAM, kernel size, and probably the phase of the moon. :-) > So now I understand that it's alright for the free memory to be low. > I don't understand how the inactive, cache, and buffered memory are > used though. When a process uses up all the free memory, does it then > use some from inactive, or does it use swap? A process will start reusing inactive memory, which involves flushing data to disk and/or using swap, depending, but the VM system may well swap out pages from other processes instead (especially ones that have been idle for a long time). [ The VM pager uses LRU or actually NFU page selection algorithms with complex names like "second chance replacement via clock hand sweep, with working set size and global page-fault frequency modelling". :-) This is a complicated topic, and it starts becoming better to look at the code than to try to describe the algorithms in words. ] -- -Chuck
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