Date: Sun, 05 Apr 1998 19:22:47 -0700 From: David Greenman <dg@root.com> To: "David E. Tweten" <tweten@frihet.com> Cc: Dan Swartzendruber <dswartz@druber.com>, dyson@FreeBSD.ORG, dag-erli@ifi.uio.no, stable@FreeBSD.ORG Subject: Re: swap-leak in 2.2.5 ? Message-ID: <199804060222.TAA17549@implode.root.com> In-Reply-To: Your message of "Sun, 05 Apr 1998 18:40:39 PDT." <199804060140.SAA03046@ns.frihet.com>
next in thread | previous in thread | raw e-mail | index | archive | help
>dswartz@druber.com said: >>Here's an off-the-cuff idea: since the confusing usage of swap as a >>caching mechanism is only a performance optimization, how bogus would >>it be to not report it. Lie. If my workstation has 64MB of swap set >>up, 8 of which is being used for real backing store, and 12 of which >>is being used to cache filesystem pages, have swapinfo lie and report >>only 8MB in use. > >The 4.4 BSD interaction between physical pages used for virtual memory and >physical pages used for file system cache doesn't work that way, and I can't >imagine the FreeBSD core team adding in such a botch. It is never a good >idea to send a dirty file system cache page to swap. ...and of course we didn't. I don't know where the confusion started on this, but what we page out to swap is the same thing we've always paged out to swap: 'anonymous' memory that is not backed by a file. Modified file pages (non-COW) are backed by the file and are never written to swap. >What you see in swap under heavy I/O load, is dirty process virtual memory >pages moved out of real memory to make way for an expanding file system >cache. There's no reason to read them back until the process faults for >them; it might exit first, allowing you to just abandon them. Right. -DG David Greenman Core-team/Principal Architect, The FreeBSD Project To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-stable" in the body of the message
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?199804060222.TAA17549>