On Mon, 27 Mar 2000, Linda Walsh wrote:
> Marco Colombo wrote:
> > > Does the kernel actually allocate all of these and just "not use
> > > them" -- i.e. are these really cases of where space is allocated and then goes
> > > unused? I'd think all of these are cases where the kernel was expecting to
> >
> > Yes. Everytime you malloc() something, use it, and no one else reclaims
> > that RAM. Swap space is not used. Why allocate it at malloc() time?
> > Just allocate it when neeed.
> ---
> "malloc"? You were talking kmalloc and the kernel reserving space
> for its *internal* data structures. Does the kernel mark address space
> withing itself (kernel space) as 'available' but not actually claim a
> physical page to map it to? I really really hope not.
Sorry. The whole thread is about what the kernel does when a process
performs a malloc() (brk() or mmap()). I didn't realize you were talking
of *kernel* allocation. AFAIK, but haven't checked the Source recently,
you can't page-fault in kernel mode. So every kernel page is valid (mapped
to a page-frame).
> > > But we already do bookkeeping for 'free'
> > > memory, 'used' memory, 'shared' memory -- would adding 'committed' or 'reserved'
> > > memory really be that much more difficult or costly?
> >
> > 'reserved' memory? You mean mlock()ed one? Of course it does bookkeeping
> > of it.
> ---
> Reserved meaning removed from the 'free' pool -- that there is
> a guaranteed space in the physical mem/swap pool (whther or not the mapping
> has actually taken place).
Some kernel allocations should succeed even if we're at the low watermark.
That space (page-frames) is "reserved" for kernel use.
I don't think the kernel is interested in using the swap for its own
address space. B-) So no need to reserve some for kernel use.
>
> -l
>
> --
> Linda A Walsh | Trust Technology, Core Linux, SGI
> law@sgi.com | Voice: (650) 933-5338
>
.TM.
--
____/ ____/ /
/ / / Marco Colombo
___/ ___ / / Technical Manager
/ / / ESI s.r.l.
_____/ _____/ _/ Colombo@ESI.it
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