Date: Fri, 28 Mar 2003 09:10:32 -0800 From: Wes Peters <wes@softweyr.com> To: "Poul-Henning Kamp" <phk@phk.freebsd.dk>, David Schultz <das@FreeBSD.ORG> Cc: freebsd-arch@FreeBSD.ORG Subject: Re: Patch to protect process from pageout killing Message-ID: <200303280910.32307.wes@softweyr.com> In-Reply-To: <14382.1048580753@critter.freebsd.dk> References: <14382.1048580753@critter.freebsd.dk>
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On Tuesday 25 March 2003 00:25, Poul-Henning Kamp wrote:
>
> As I see it, there is a need for several mechanisms:
>
> 1. A mechanism to export to userland enough information about the
> current RAM availability, so that phkmalloc and application
> specific code can make intelligent choices before things go bad.
>
> 2. A mechanism to alert userland to the fact that things _have_ gone
> bad.
>
> 3. A mechanism to influence the "Who do we kill ?" decision once
> things have gone from bad to worse.
>
> To tackle them from behind:
>
> Wes has a proposal for #3 which is a per-process flag which says
> "I'm sacred". I think that is a sound principle since that is
> usually exactly what people want: Do Not Kill This Process.
>
> Certain processes already enjoy special protection, pid==1 most
> notably, this would just be a way to make the same protection
> available to other processes. I'm not happy about using the
> resourcelimit code for booleans, and I don't think the flag
> should be inherited, but otherwise I'm for the idea.
I've reworked my patch to use the madvise(2) syscall, like the original
4.x patch did. I've even documented it, in a man page of all places.
Please see attached patch. If nobody objects, I'll commit sometime this
weekend.
> We have the SIGDANGER proposal for #2, but I think we need to have
> two severities: "Out of RAM" and "Out of VM". A program like
> fsck would start to recycle cached sectors once we're out of RAM.
I'll work with Garance to create a proposal, some pseudocode, something
like a design. Then we can bikeshed that. Mike Murphy is helping
silently at work, letting me bounce ideas off him and look at the man
pages on his AIX machine.
> But I have not seen anybody come up with a good proposal for
> #1, and that is where the main benefit would be derived: It would
> allow processes to be good citizens and adjust to the present
> situation.
Added to think-about queue...
--
Where am I, and what am I doing in this handbasket?
Wes Peters wes@softweyr.com
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