Date: Tue, 9 Jun 2009 23:24:50 -0700 From: Kip Macy <kmacy@freebsd.org> To: Dmitry Morozovsky <marck@rinet.ru> Cc: svn-src-head@freebsd.org, svn-src-all@freebsd.org, src-committers@freebsd.org Subject: Re: svn commit: r193878 - head/sys/cddl/contrib/opensolaris/uts/common/fs/zfs Message-ID: <3c1674c90906092324n58e16154s6800e61752282e42@mail.gmail.com> In-Reply-To: <alpine.BSF.2.00.0906101013480.49870@woozle.rinet.ru> References: <200906100121.n5A1LWVO089719@svn.freebsd.org> <alpine.BSF.2.00.0906101013480.49870@woozle.rinet.ru>
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On Tue, Jun 9, 2009 at 11:15 PM, Dmitry Morozovsky<marck@rinet.ru> wrote: > Kip, > > On Wed, 10 Jun 2009, Kip Macy wrote: > > KM> Author: kmacy > KM> Date: Wed Jun 10 01:21:32 2009 > KM> New Revision: 193878 > KM> URL: http://svn.freebsd.org/changeset/base/193878 > KM> > KM> Log: > KM> =A0 As far as I can tell systems that have less than 4GB are more oft= en hurt > KM> =A0 by prefetched than helped. =A0On i386 systems and systems with le= ss than 4GB, > KM> =A0 prefetch is now disabled by default. I've added a prefetch enable= tunable, to > KM> =A0 enable prefetching for those systems. The prefetch disable tunabl= e will continue > KM> =A0 to unconditionally disable prefetching. > KM> > > [snip] > > KM> +extern int zfs_prefetch_disable; > KM> +extern int zfs_prefetch_enable; > > [snip] > > Before the interface is not settled in stone, don't you think simple bool > zfs_prefetch tunable (defauled to what looks more reasonable to partucila= r > arch/memsize) is more clean and straightforward? > Yes. But the semantics I want don't lend themselves well to a boolean. I want it to default to off for i386 and amd64 w/ < 4GB and on for amd64 > 4GB. However, I want it to be possible for users with larger memory systems to disable it and users with smaller memory systems to enable it. The only way a simple boolean would work would be if it were zfs_prefetch_non_default_behavior, which I think is even more confusing than what I have now. Cheers, Kip
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