Date: Wed, 10 Jun 2009 00:08:43 -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: <3c1674c90906100008i4c632312j32f223b8aca14934@mail.gmail.com> In-Reply-To: <alpine.BSF.2.00.0906101058140.49870@woozle.rinet.ru> References: <200906100121.n5A1LWVO089719@svn.freebsd.org> <alpine.BSF.2.00.0906101013480.49870@woozle.rinet.ru> <3c1674c90906092324n58e16154s6800e61752282e42@mail.gmail.com> <alpine.BSF.2.00.0906101058140.49870@woozle.rinet.ru>
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On Wed, Jun 10, 2009 at 12:00 AM, Dmitry Morozovsky<marck@rinet.ru> wrote: > On Tue, 9 Jun 2009, Kip Macy wrote: > > KM> > KM> =A0 As far as I can tell systems that have less than 4GB are mo= re often hurt > KM> > KM> =A0 by prefetched than helped. =A0On i386 systems and systems w= ith less than 4GB, > KM> > KM> =A0 prefetch is now disabled by default. I've added a prefetch = enable tunable, to > KM> > KM> =A0 enable prefetching for those systems. The prefetch disable = tunable will continue > KM> > KM> =A0 to unconditionally disable prefetching. > KM> > KM> > KM> > > KM> > [snip] > KM> > > KM> > KM> +extern int zfs_prefetch_disable; > KM> > KM> +extern int zfs_prefetch_enable; > KM> > > KM> > [snip] > KM> > > KM> > Before the interface is not settled in stone, don't you think simpl= e bool > KM> > zfs_prefetch tunable (defauled to what looks more reasonable to par= tucilar > KM> > arch/memsize) is more clean and straightforward? > KM> > > KM> > KM> Yes. But the semantics I want don't lend themselves well to a boolean= . > KM> I want it to default to off for i386 and amd64 w/ < 4GB and on for > KM> amd64 > 4GB. However, I want it to be possible for users with larger > KM> memory systems to disable it and users with smaller memory systems to > KM> enable it. The only way a simple boolean would work would be if it > KM> were zfs_prefetch_non_default_behavior, which I think is even more > KM> confusing than what I have now. > > Hmm, I failed to see how boolean prevent the usage: > > if arch=3D=3Di386 || memsize < 4G > =A0 =A0 =A0 =A0zfs_prefetch=3D0 > else > =A0 =A0 =A0 =A0zfs_prefetch=3D1 > > and admin can flip the switch to non-default position. > Right, what you're advocating is zfs_prefetch_non_default. Which is simpler, but still rather weird. I'll ask around. Cheers, Kip
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