From owner-freebsd-hackers  Thu Dec 24 12:08:31 1998
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Date: Thu, 24 Dec 1998 11:59:46 -0800 (PST)
From: Julian Elischer <julian@whistle.com>
To: Matthew Dillon <dillon@apollo.backplane.com>
cc: "John S. Dyson" <dyson@iquest.net>, hackers@FreeBSD.ORG
Subject: Re: M_KERNEL in sys/malloc.h ???
In-Reply-To: <199812241721.JAA27982@apollo.backplane.com>
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I would rename it to M_RESERVED or something that indicates
that this is a request that is allowed dip into the emergency reserves
to satisfy the request.


On Thu, 24 Dec 1998, Matthew Dillon wrote:

> 
> :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.
> 
>     Ok, I'll document it then and make sure it operates the same with my
>     cleanups.
> 
> 					    -Matt
> 
> :John                  | Never try to teach a pig to sing,
> :dyson@iquest.net      | it makes one look stupid
> 
>     Matthew Dillon  Engineering, HiWay Technologies, Inc. & BEST Internet 
>                     Communications & God knows what else.
>     <dillon@backplane.com> (Please include original email in any response)    
> 
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