Date: Wed, 10 Jun 2009 11:00:00 +0400 (MSD) From: Dmitry Morozovsky <marck@rinet.ru> To: Kip Macy <kmacy@freebsd.org> 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: <alpine.BSF.2.00.0906101058140.49870@woozle.rinet.ru> In-Reply-To: <3c1674c90906092324n58e16154s6800e61752282e42@mail.gmail.com> References: <200906100121.n5A1LWVO089719@svn.freebsd.org> <alpine.BSF.2.00.0906101013480.49870@woozle.rinet.ru> <3c1674c90906092324n58e16154s6800e61752282e42@mail.gmail.com>
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On Tue, 9 Jun 2009, Kip Macy wrote: KM> > KM> As far as I can tell systems that have less than 4GB are more often hurt KM> > KM> by prefetched than helped. On i386 systems and systems with less than 4GB, KM> > KM> prefetch is now disabled by default. I've added a prefetch enable tunable, to KM> > KM> enable prefetching for those systems. The prefetch disable tunable will continue KM> > KM> 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 simple bool KM> > zfs_prefetch tunable (defauled to what looks more reasonable to partucilar 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==i386 || memsize < 4G zfs_prefetch=0 else zfs_prefetch=1 and admin can flip the switch to non-default position. Or, do you think it's not clean for the user? -- Sincerely, D.Marck [DM5020, MCK-RIPE, DM3-RIPN] [ FreeBSD committer: marck@FreeBSD.org ] ------------------------------------------------------------------------ *** Dmitry Morozovsky --- D.Marck --- Wild Woozle --- marck@rinet.ru *** ------------------------------------------------------------------------
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