Date: Sat, 12 Jan 2008 00:05:38 -0500 From: John Baldwin <jhb@freebsd.org> To: freebsd-stable@freebsd.org Cc: Peter Jeremy <peterjeremy@optushome.com.au>, Kris Kennaway <kris@freebsd.org> Subject: Re: Swapping caused by very large (regular) file size Message-ID: <200801120005.38972.jhb@freebsd.org> In-Reply-To: <20080112033147.GX60060@server.vk2pj.dyndns.org> References: <20071203054207.GA1153@aleph.niw.com.au> <4787AAF4.1020905@FreeBSD.org> <20080112033147.GX60060@server.vk2pj.dyndns.org>
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On Friday 11 January 2008 10:31:47 pm Peter Jeremy wrote: > On Fri, Jan 11, 2008 at 06:44:20PM +0100, Kris Kennaway wrote: > >Ian West wrote: > >> dd if=/dev/zero bs=32768 of=junkfile count=100000 seems to do it quite > >> reliably on all the boxes I have tested ? > > > >I am unable to reproduce this on 7.0. > > I can't reproduce it on 6.3-PRERELEASE/amd64 with 1GB RAM. > > vmstat -s;dd if=/dev/zero bs=32768 of=junkfile count=100000;vmstat -s > shows the following changes: > 2 swap pager pageins > 2 swap pager pages paged in > 4 swap pager pageouts > 5 swap pager pages paged out > 24 vnode pager pageins > 78 vnode pager pages paged in > 0 vnode pager pageouts > 0 vnode pager pages paged out You may not have a fast enough disk. We have noticed an issue at work but only on faster controllers (e.g. certain mfi(4) drive configurations) when doing I/O to a single file like the dd command mentioned causes the buffer cache to fill up. The problem being that we can't lock the vm object to recycle pages when we hit the limit that is supposed to prevent this because all the pages in the cache are for the file (vm object) we are working on. Stephan (ups@) says this is fixed in 7. The tell-tale sign that we see is pagedaemon starts chewing up lots of CPU as the kernel tries to realign the page queues along with I/O throughput going down the toilet and being very erratic. -- John Baldwin
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