Date: Thu, 24 Dec 1998 03:08:18 -0500 (EST) From: "John S. Dyson" <dyson@iquest.net> To: dillon@apollo.backplane.com (Matthew Dillon) Cc: hackers@FreeBSD.ORG Subject: Re: M_KERNEL in sys/malloc.h ??? Message-ID: <199812240808.DAA46738@y.dyson.net> In-Reply-To: <199812230019.QAA08154@apollo.backplane.com> from Matthew Dillon at "Dec 22, 98 04:19:43 pm"
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Matthew Dillon said:
> Does anyone know what M_KERNEL is sys/malloc.h is supposed to do? It
> is used in precisely two places in the code as far as I can tell:
>
> vm/default_pager.c: if (swap_pager_swp_alloc(object, M_KERNEL) != 0) {
> vm/default_pager.c: if (swap_pager_swp_alloc(object, M_KERNEL) != 0) {
> vm/swap_pager.c: spc->spc_bp = malloc(sizeof(*bp), M_TEMP, M_KERNEL);
>
> But kern/kern_malloc.c doesn't appear to really use it. On the otherhand
> I do see lots of absolute comparison of the malloc 'flags' to M_WAITOK
> (0) or M_NOWAIT which the use of M_KERNEL would interfere with. I can't
> tell if the side effects are something that are expected, or if the
> side effects are a bug.
>
> Anybody know?
>
As I remember, M_KERNEL means that it really needs memory. waiting
for memory is bad, and dip deeply into the page reserves. Normally, the
malloc (in vm_kern) code will only dip into the interrupt accessible
free pages. The M_KERNEL allows it to dip into all of the pages.
--
John | Never try to teach a pig to sing,
dyson@iquest.net | it makes one look stupid
jdyson@nc.com | and it irritates the pig.
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