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: ma...@freebsd.org ]
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*** Dmitry Morozovsky --- D.Marck --- Wild Woozle --- ma...@rinet.ru ***
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