Date: Sun, 5 Aug 2001 12:55:46 -0700 (PDT) From: Matt Dillon <dillon@earth.backplane.com> To: Zhihui Zhang <zzhang@cs.binghamton.edu> Cc: freebsd-hackers@FreeBSD.ORG Subject: Re: Allocate a page at interrupt time Message-ID: <200108051955.f75Jtk882156@earth.backplane.com> References: <Pine.SOL.4.21.0108031432070.28997-100000@opal>
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:I should have guessed the reason. Matthew Dillon answered this question on
:Fri, 2 Jun 2000 as follows:
:
:
: The VM routines that manage pages associated with objects are not
: protected against interrupts, so interrupts aren't allowed to change
: page-object associations. Otherwise an interrupt at just the wrong
: time could corrupt the mainline kernel VM code.
:
:
:On Thu, 2 Aug 2001, Zhihui Zhang wrote:
:
:>
:> FreeBSD can not allocate from the PQ_CACHE queue in an interrupt context.
:> Can anyone explain it to me why this is the case?
:>
:>
:> Thanks,
Yes, that is precisely the reason. In -current this all changes, though,
since interrupts are now threads. *But*, that said, interrupts cannot
really afford to hold mutexes that might end up blocking them for
long periods of time so I would still recommend that interrupt code not
attempt to allocate pages out of PQ_CACHE.
-Matt
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