Date: Thu, 28 Jul 2005 10:28:44 +0200 From: Pawel Jakub Dawidek <pjd@FreeBSD.org> To: Julian Elischer <julian@elischer.org> Cc: FreeBSD Current <freebsd-current@freebsd.org> Subject: Re: Apparent strange disk behaviour in 6.0 Message-ID: <20050728082844.GW46538@darkness.comp.waw.pl> In-Reply-To: <42E88F2B.5000108@elischer.org> References: <42E88135.30603@elischer.org> <42E88F2B.5000108@elischer.org>
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On Thu, Jul 28, 2005 at 12:54:19AM -0700, Julian Elischer wrote:
+> it APPEARS that teh system is swapping out running programs in order to
+> store more write data!
+>
+> experiment:
+> boot to single user mode.
+> type:
+> mount {big partition}
+> dd if=/dev/zero bs=128K of=/$bigpartition}/bigfile count=1000000
+>
+> notice that after a short while your dd is killed because the system is
+> out of swapspace.
+> (it doesn't have any)
+> Why the F*ck does it need swapspace.? there are exactly 2 proceses
+> running in userspace
+> and one of them s in wait4(). dd shows a resident size of about 170KB
+> leaving about a GIGABYTE of unused RAM.
+>
+> The system should make dd wait rather than trying to swap its pages out..
+>
+>
+> if you then do
+> swapon (your swap device)
+> and repeat teh command in the background,
+> vmstat 1 will show you pages being faulted in and out...
+> no WONDER IO goes to hell in a handbasket..
+>
+> Outgoing IO should never be able to force running programs out!
+> It should start re-using old pages from the same file!
+>
+> 4.11 gives a consinstent 65MB/sec with this array, for as long as I run it..
+> 6.0 gives me 65MB for 15 seconds and then it drops to 20MB/sec and then
+> 10MB/sec
+> and the swap disk bursts into life.
+>
+> the array goes from all the lights solidly on, to bursts of activity
+> with large gaps in between them.
It looks I observed the same behaviour!
I was testing GELI GEOM class and I was getting ENOMEM errors from malloc(9).
Then, I was sure I've a memory leak, but this was only 'vmstat -m' issue so
there was no memory leak and I shouldn't get ENOMEM in the first place while
copying /usr/src/sys directory.
I'm also able to reproduce your dd(1) test easly.
Not sure when it was introduced...
--
Pawel Jakub Dawidek http://www.wheel.pl
pjd@FreeBSD.org http://www.FreeBSD.org
FreeBSD committer Am I Evil? Yes, I Am!
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