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SubjectRe: RFT: updatedb "morning after" problem [was: Re: -mm merge plans for 2.6.23]
On Thu, 26 Jul 2007 11:40:24 +0200 Ingo Molnar <mingo@elte.hu> wrote:

>
> * Andrew Morton <akpm@linux-foundation.org> wrote:
>
> > On Thu, 26 Jul 2007 11:20:25 +0200 Ingo Molnar <mingo@elte.hu> wrote:
> >
> > > Once we give the kernel the knowledge that the dentry wont be used again
> > > by this app, the kernel can do a lot more intelligent decision and not
> > > baloon the dentry cache.
> > >
> > > ( we _do_ want to baloon the dentry cache otherwise - for things like
> > > "find" - having a fast VFS is important. But known-use-once things
> > > like the daily updatedb job can clearly be annotated properly. )
> >
> > Mutter. /proc/sys/vm/vfs_cache_pressure has been there for what,
> > three years? Are any distros raising it during the updatedb run yet?
>
> but ... that's system-wide, and the 'dont baloon the dcache' is only a
> property of updatedb.

Sure, but it's practical, isn't it? Who runs (and cares about)
vfs-intensive workloads during their wee-small-hours updatedb run?

(OK, I do, but I kill the damn thing if it goes off)

> Still, it's useful to debug this thing.
>
> below is an updatedb hack that sets vfs_cache_pressure down to 0 during
> an updatedb run. Could someone who is affected by the 'morning after'
> problem give it a try? If this works then we can think about any other
> measures ...
>
> Ingo
>
> --- /etc/cron.daily/mlocate.cron.orig
> +++ /etc/cron.daily/mlocate.cron
> @@ -1,4 +1,7 @@
> #!/bin/sh
> nodevs=$(< /proc/filesystems awk '$1 == "nodev" { print $2 }')
> renice +19 -p $$ >/dev/null 2>&1
> +PREV=`cat /proc/sys/vm/vfs_cache_pressure 2>/dev/null`
> +echo 0 > /proc/sys/vm/vfs_cache_pressure 2>/dev/null
> /usr/bin/updatedb -f "$nodevs"
> +[ "$PREV" != "" ] && echo $PREV > /proc/sys/vm/vfs_cache_pressure 2>/dev/null

Setting it to zero will maximise the preservation of the vfs caches. You
wanted 10000 there.
<bets that nobody will test this>
-
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