Date: Wed, 22 Jan 2003 16:58:05 -0500 (EST) From: John Baldwin <jhb@FreeBSD.org> To: Andrew Gallatin <gallatin@cs.duke.edu> Cc: arch@FreeBSD.ORG Subject: Re: M_ flags summary. Message-ID: <XFMail.20030122165805.jhb@FreeBSD.org> In-Reply-To: <15919.4208.394911.712558@grasshopper.cs.duke.edu>
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On 22-Jan-2003 Andrew Gallatin wrote:
>
>
> Speaking as the token 3rd party driver vendor, the removal of
> M_WAITOK/M_TRYWAIT is irritating, but not something that can't be
> solved with yet another ifdef in my driver. Breaking the 5.0 ABI
> prior to 5.1 is no big deal to me, as I don't plan to support
> 5.0-RELEASE anyway, so I don't care what the #defines end up as in the
> 5.0-STABLE branch.
>
> My thoughts are that whether we pronounce it po-ta-to, or po-tat-o,
> its still a potato and how its pronounced doesn't matter nearly as
> much as how it tastes.
>
> The taste "problem" here is that it always used to be safe to sleep
> in a process context. That's not true anymore. Now its safe to
> sleep in a process context if you're not holding any mutexes. So
> there are pleny of sleepable allocation bugs lurking.
>
> If we want to catch sleepable allocation bugs right up front, I
> suggest we put this:
>
> if (!(flags & M_NOWAIT)) {
> WITNESS_SLEEP(1, NULL);
> }
>
> at the top of malloc, and at the top of all entry points to the mbuf
> allocator. Eg, before the system has a chance to pull the allocation
> off of some cache which will succeed 99.5% of the time, except when
> the system is under memory pressure.
We already do this for malloc(), that is the source of most of the
'could sleep' messages these days. I have some patches I need to
commit to make the actual message more informative so that it will
say 'could malloc' etc.
--
John Baldwin <jhb@FreeBSD.org> <>< http://www.FreeBSD.org/~jhb/
"Power Users Use the Power to Serve!" - http://www.FreeBSD.org/
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