Messages in this thread | ![/](/images/icornerl.gif) | | Date | Mon, 24 Nov 2003 17:05:06 -0800 | From | Andrew Morton <> | Subject | Re: [RFC] Make balance_dirty_pages zone aware (1/2) |
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"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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