From: Andrew Morton <akpm@osdl.org>
To: "Martin J. Bligh" <mbligh@aracnet.com>
Cc: colpatch@us.ibm.com, linux-kernel@vger.kernel.org, linux-mm@kvack.org
Subject: Re: [RFC] Make balance_dirty_pages zone aware (1/2)
Date: Mon, 24 Nov 2003 17:05:06 -0800 [thread overview]
Message-ID: <20031124170506.4024bb30.akpm@osdl.org> (raw)
In-Reply-To: <39670000.1069719009@flay>
"Martin J. Bligh" <mbligh@aracnet.com> wrote:
>
> > What trouble?
>
> Well ... not so sure of this as I once was ... so be gentle with me ;-)
> But if the system has been running for a while, memory is full of pagecache,
> etc. We try to allocate from the local node, fail, and fall back to the
> other nodes, which are all full as well. Then we wake up kswapd, but all
> pages in this node are dirty, so we block for ages on writeout, making
> mem allocate really latent and slow (which was presumably what
> balance_dirty_pages was there to solve in the first place).
It is possible. You'd be pretty unlucky to dirty so much lowmem when there
is such a huge amount of highmem floating about, but yes, if you tried hard
enough...
I have a feeling that some observed problem must have prompted this coding
frenzy from Matthew. Surely some problem was observed, and this patch
fixed it up??
> > If we make the dirty threshold a proportion of the initial amount of free
> > memory in ZONE_NORMAL, as is done in 2.4 it will not be possible to fill
> > any node with dirty pages.
>
> True. But that seems a bit extreme for a system with 64GB of RAM, and only
> 896Mb in ZONE_NORMAL ;-) Doesn't really seem like the right way to fix it.
>
Increasing /proc/sys/vm/lower_zone_protection can be used to teach the VM
to not use lowmem for pagecache. Does this solve the elusive problem too?
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next prev parent reply other threads:[~2003-11-25 1:05 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2003-11-22 0:49 Matthew Dobson
2003-11-23 22:36 ` Andrew Morton
2003-11-24 15:36 ` Martin J. Bligh
2003-11-24 18:00 ` Andrew Morton
2003-11-25 0:10 ` Martin J. Bligh
2003-11-25 1:05 ` Andrew Morton [this message]
2003-11-25 4:58 ` Martin J. Bligh
2003-11-25 5:14 ` Andrew Morton
2003-11-25 5:23 ` Andrew Morton
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