Date: Fri, 14 Aug 1998 13:10:00 -0700 (PDT) From: Luoqi Chen <luoqi@watermarkgroup.com> To: freebsd-bugs@FreeBSD.ORG Subject: Re: kern/7418 (file corruption on mmap-based-read during file write()) Message-ID: <199808142010.NAA00264@freefall.freebsd.org>
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The following reply was made to PR kern/7418; it has been noted by GNATS. From: Luoqi Chen <luoqi@watermarkgroup.com> To: dillon@backplane.com, luoqi@watermarkgroup.com Cc: freebsd-gnats-submit@freebsd.org, luoqi@chen.ml.org Subject: Re: kern/7418 (file corruption on mmap-based-read during file write()) Date: Fri, 14 Aug 1998 16:00:41 -0400 (EDT) > I've tried writing similar test programs, with no luck either. The > load on the real machine has got to be a significant factor, but since > the memory isn't starved I'm tending towards the disk latency as being > a possible factor. > Just a hunch, would you try a kernel with double the number of buffer headers and see if the rate of corruption would drop? Currently the default number of buffers `nbuf' is 2078, which amounts to about 16M of data for 8K blocks, that's barely enough for a heavy load news server. For a diablo server, there's effectively just one writing process, but with scores of readers, so there disk latency should not be too big, unless the readers trying to allocate scarce buf headers are forcing many delayed writes to be committed to disk immediately. If increasing buffer count could reduce disk latency, then it should also reduce number of corruptions. Use config option `options NBUF=nnnn' to override the default. And I will try a nbuf reduced kernel on a light-load machine and see if I can produce some corruptions. -lq > -Matt > > Matthew Dillon Engineering, HiWay Technologies, Inc. & BEST Internet > Communications > <dillon@backplane.com> (Please include original email in any response) > To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-bugs" in the body of the message
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