> Followup to: <[EMAIL PROTECTED]>
> By author: Kenn Humborg <[EMAIL PROTECTED]>
> In newsgroup: linux.dev.kernel
> >
> > On Sun, Mar 04, 2001 at 11:41:12PM +0100, Manfred Spraul wrote:
> > > >
> > > > Does kmalloc() make any guarantees of the alignment of allocated
> > > > blocks? Will the returned block always be 4-, 8- or 16-byte
> > > > aligned, for example?
> > > >
> > >
> > > 4-byte alignment is guaranteed on 32-bit cpus, 8-byte alignment on
> > > 64-bit cpus.
> >
> > So, to summarise (for 32-bit CPUs):
> >
> > o Alan Cox & Manfred Spraul say 4-byte alignment is guaranteed.
> >
> > o If you need larger alignment, you need to alloc a larger space,
> > round as necessary, and keep the original pointer for kfree()
> >
> > Maybe I'll just use get_free_pages, since it's a 64KB chunk that
> > I need (and it's only a once-off).
My old kmalloc would actually use n+10 bytes if you request n bytes.
As memory comes in pools of powers of two, if you request 64k, you
would acutaly use 128k of memory. If you use "get_free_pages", you'll
not have the overhead, and actually allocate the 64k you need.
I'm not sure what the slab stuff does...
Roger.
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