Date: Thu, 20 Dec 2001 14:26:24 -0800 (PST) From: Julian Elischer <julian@elischer.org> To: Poul-Henning Kamp <phk@critter.freebsd.dk> Cc: John Baldwin <jhb@FreeBSD.org>, arch@FreeBSD.org, Alfred Perlstein <bright@mu.org> Subject: Re: Kernel stack size and stacking: do we have a problem ? Message-ID: <Pine.BSF.4.21.0112201412310.46573-100000@InterJet.elischer.org> In-Reply-To: <3954.1008885976@critter.freebsd.dk>
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On Thu, 20 Dec 2001, Poul-Henning Kamp wrote:
>
> A) We should probably implement
> int enough_stack()
a full unoptimised but correct version would be:
int
enough_stack(u_int needed)
{
caddr_t addr, addr2;
if needed > KSTACK_PAGES * PAGESIZE return 0;
/* catch stupid values */
addr1 = &needed;
addr2 = (caddr_t)curthread->td_kstack + needed;
return (addr1 > addr2)
}
> and apply it in some strategic places so we can fail gracely
> rather than panic when we run out of kernel stack.
>
> B) We have no idea how to sanely fix VOP_ since it is synchronous.
> When I say "sanely" I'm referring to the fact that the VOP
> code is scary enough as it is and we don't want to make it even
> hairier, lest we loose the few filesystem hackers we have, not
> to mention the fact that we would probably never complete the
> conversion in the first place (see sys/vnode.h::IS_LOCKING_VFS()
> for precedent.)
>
> C) Variant size kernel stacks are probably not worth the bother,
> but sysctl variable kernel stacks might be a good investment.
>
> C) Netgraph and Geom will use scheduling, possibly with a direct
> call optimization to avoid the issue.
> Julian hybrid scheme could possibly be adapted to Geom, if it
> can be made to maintain ordering (think: softupdates).
it does..
>
> Thanks for your input gentlemen.
The netgraph locking/queueing is an integrated set of code that does both
functions. The queing is part and parcel of the locking. it wouldn't work
if it were not an async system.
>
> --
> Poul-Henning Kamp | UNIX since Zilog Zeus 3.20
> phk@FreeBSD.ORG | TCP/IP since RFC 956
> FreeBSD committer | BSD since 4.3-tahoe
> Never attribute to malice what can adequately be explained by incompetence.
>
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