Date: Thu, 04 Sep 1997 23:36:02 +0930 From: Mike Smith <mike@smith.net.au> To: Brian Campbell <brianc@pobox.com> Cc: freebsd-hackers@FreeBSD.ORG Subject: Re: 2.2-stable swap usage? Message-ID: <199709041406.XAA01388@word.smith.net.au> In-Reply-To: Your message of "Thu, 04 Sep 1997 00:08:12 -0400." <19970904000812.60761@pobox.com>
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> Mike Smith said: > > The simple answer is that once swap is allocated to a process, it is > > never freed. You have, in the case above, 24M worth of text which at > > some stage has been swapped out, and thus has had swap allocated to it. > > It doesn't mean you have 24M worth of swap currently "in use". > > John S. Dyson wrote: > > Once the pages in MFS or any other process are paged out, those pages will be > > persistant in swap until the process exits (or the memory is explicitly > > deallocated by the process.) > > Ok. So, contrary to what Mike Smith says, pages that belonged to > a process that has since exited will no longer be marked in-use by > swap? I didn't say that; I said once it's been given to a process, it's never taken back. If it's backing memory that the process has freed, it will be returned. Once the process exits, naturally swap will be freed; the system would starve without this. > If they are still marked "in-use", is there a program other than > pstat that gives a more accurate picture of how many [active] pages > are in swap? That'd be horrifically difficult to determine at any given point in time. You could look at the figures given by 'systat -vmstat' and in particular the amount of "active" memory, but how you go about deciding what is in use by processes as opposed to by the buffer cache is not clear. > > MFS doesn't deallocate any of it's memory usage. > > So, if 90% of MFS is consumed by files which are later unlinked > (and not in use by any process), is swap thereafter limited to 10% > of its original size? That sounds reasonable. mike
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