Date: Mon, 24 Mar 2003 18:05:38 -0800 From: Wes Peters <wes@softweyr.com> To: "Poul-Henning Kamp" <phk@phk.freebsd.dk> Cc: freebsd-arch@freebsd.org Subject: Re: Patch to protect process from pageout killing Message-ID: <200303241805.38175.wes@softweyr.com> In-Reply-To: <7019.1048523782@critter.freebsd.dk> References: <7019.1048523782@critter.freebsd.dk>
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On Monday 24 March 2003 08:36, Poul-Henning Kamp wrote:
> In message <200303240823.48262.wes@softweyr.com>, Wes Peters writes:
> >As promised, here's the patch to protect a process from being killed
> > when pageout is in memory shortage. This allows a process to
> > specify that it is important enough to be skipped when pageout is
> > looking for the largest process to kill.
> >
> >My needs are simple. We make a box that is a web proxy and runs
> > from a memory disk, using flash for permanent storage. The flash
> > is mounted only when a configuration write is needed, the box runs
> > from the memory disk. We've experienced a problem at certain
> > customer sites where bind will consume a lot (~30 MB) of ram and
> > then pageout will kill the largest process, which is usually either
> > named or squid. This pretty much kills the box. We'd much rather
> > have pageout kill off some of the squid worker processes, we can
> > recover from that.
> >
> >Is this a good approach to the problem? Feedback welcome.
>
> (Ignoring the white-space change)
OK, I put them back so the function will be inconsistent again. ;^)
They accidentally got shuffled when I move my implementation from just
below RLIMIT_CPU (from which it obviously and erroneously heavily
borrowed) to put it in numerical order.
> I can certainly see the point, but I'm not sure this is the way.
>
> I am not sure that we want to use the resource limits facility for
> booleans, some of the logic sourounding the suser checks may not
> hold tight.
I had concerns about that as well. In the original (4.4 roughly)
implementation I used madvise as the interface, but the madvise
interface has changed greatly. It didn't seem worthwhile adding a
syscall for this task, so I looked for another reasonable protected
interface to ab(use). I'm 100% open to suggestions on the API.
> Also, doesn't this result in the flag being inerited with fork() and
> thereby negating the effect you are seeking for squid ?
I looked through all the places in kern_fork.c where p2->p_flag gets set
and didn't see anything that looked like it would inherit P_PROTECTED
from p1->p_flag. Did I miss something? I'm obviously a bit of a
neophyte in this part of the kernel.
--
"Where am I, and what am I doing in this handbasket?"
Wes Peters wes@softweyr.com
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