Date: Fri, 11 Apr 2003 18:38:47 +1000 (EST) From: Bruce Evans <bde@zeta.org.au> To: Lucky Green <shamrock@cypherpunks.to> Cc: freebsd-current@freebsd.org Subject: Re: options NO_SWAPPING, still wants swap Message-ID: <20030411182925.A3507@gamplex.bde.org> In-Reply-To: <20030410230113.M81717@pakastelohi.cypherpunks.to> References: <20030410230113.M81717@pakastelohi.cypherpunks.to>
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On Thu, 10 Apr 2003, Lucky Green wrote: > I compiled a kernel with "options NO_SWAPPING", yet CURRENT still > attempts to allocate swap space: NO_SWAPPING has nothing to do with not allocating swap space. It prevents swapping of upages and stack pages only. Unfortunately, NOTES' description of NO_SWAPPING says that it disables swapping without explaining what swapping is (it is just swapping of upages and stack, and has nothing to do with generic VM paging). NO_SWAPPING is documented mainlly in the commitlog for the change that added it: %%% RCS file: /home/ncvs/src/sys/vm/vm_pageout.c,v Working file: vm_pageout.c head: 1.228 ... ---------------------------- revision 1.66 date: 1996/02/22 10:57:37; author: davidg; state: Exp; lines: +20 -12 Add a "NO_SWAPPING" option to disable swapping. This was originally done to help diagnose a problem on wcarchive (where the kernel stack was sometimes not present), but is useful in its own right since swapping actually reduces performance on some systems (such as wcarchive). Note: swapping in this context means making the U pages pageable and has nothing to do with generic VM paging, which is unaffected by this option. Reviewed by: <dyson> ---------------------------- %%% > As a result, everything from make to cp to httpd (on a server with no load > other than random search engine visits) sometimes fails. The machine has > 1GB of RAM, all seen by FreeBSD. Since I ran the same processes on a > machine with 128MB of RAM and 256MB of swap without ever running out of > memory, something seems broken with FreeBSD's use of memory when options > NO_SWAPPING is chosen. I always use it, with and without actual swap, and have had no problems from it. Bruce
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