Date: Wed, 15 Feb 2012 18:06:34 +0200 From: George Kontostanos <gkontos.mail@gmail.com> To: Pavlo <devgs@ukr.net> Cc: freebsd-fs@freebsd.org Subject: Re: ZFS and mem management Message-ID: <CA%2BdUSyqn8SY9G_2hXSgQ_UDEBXCd8s0HRzw%2BXLajeE461LPGLw@mail.gmail.com> In-Reply-To: <4633.1329320658.10597993752278204416@ffe16.ukr.net> References: <41082.1329320114.6955040073494560768@ffe1.ukr.net> <CA%2BdUSyp1p07ERXaL-zLG4ibGB45c7VGBNH3ALL4ZXbXUbeEDiA@mail.gmail.com> <70229.1329318412.9319724204137054208@ffe16.ukr.net> <CA%2BdUSyqRd9DFhhAtQqU%2BVdmUz_kxqo=jSApoGOUd1Q9StrCkxA@mail.gmail.com> <4633.1329320658.10597993752278204416@ffe16.ukr.net>
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2012/2/15 Pavlo <devgs@ukr.net>: > > > --- Original message --- > From: "George Kontostanos" <gkontos.mail@gmail.com> > To: "Pavlo" <devgs@ukr.net> > Date: 15 February 2012, 17:39:46 > Subject: Re: ZFS and mem management > > > > 2012/2/15 Pavlo <devgs@ukr.net>: >> >> >> 2012/2/15 Pavlo <devgs@ukr.net>: >>> >>> >>> >>>>On 15/02/2012 13:39, Pavlo wrote: >>>>> >>> >>>>> >> >> Unfortunately we can't afford disabling prefetch. It is too much >>>>> >> >> of an>> overhead.>> >> Also I made some tests. I have process >>>>> >> >> that maps file >>>>> >> >> using mmap() and>> writes or reads first byte of each page of >>>>> >> >> mapped file >>>>> >> >> with some data.> >>>>Note that ZFS is designed so that it interacts somewhat badly with >>>>mmap() and other kernel services which rely on coherency between VM and >>>>IO such as sendfile(). At the very best, you will have two in-kernel >>>>copies of all data buffers used with such interfaces, but there have >>>>been sporadic reports that there are other bugs with it. >>>> >>>>If you have a test server, I'd recommend you do the same test on UFS for >>>>comparison. >>> >>> Was going to try this... Thanks for reply. >>> _______________________________________________ >>> freebsd-fs@freebsd.org mailing list >>> http://lists.freebsd.org/mailman/listinfo/freebsd-fs >>> To unsubscribe, send any mail to "freebsd-fs-unsubscribe@freebsd.org" >> >> Why do you think that disabling prefetch is an overhead? >> >> >> -- >> George Kontostanos >> Aicom telecoms ltd >> http://www.aisecure.net >> >> >> >> Well... not me though. System administrator >_> . I suppose because we >> have >> a big IO traffic. > > Not for a highly random I/O environment. > > -- > George Kontostanos > Aicom telecoms ltd > http://www.aisecure.net > > > That's is a reason we don't disable. Our reads and writes mostly contiguous. > And that problem arises on machines with low RAM (8Gb and less). Also for > obvious reasons swap is disabled. > I guess then that a memory upgrade should be scheduled. -- George Kontostanos Aicom telecoms ltd http://www.aisecure.net
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