On Fri, Mar 24, 2006 at 02:45:35PM -0800, Andrew Morton wrote:
> The `= 0;' causes this to consume space in vmlinux's .data. If we put it
> in bss and let crt0.o take care of zeroing it, we save a little disk space.
Yup.
> > + page = alloc_page(GFP_ATOMIC);
>
> That's potentially quite a few atomically-allocated pages. I guess UML is
> more resistant to oom than normal kernels (?) but it'd be nice to be able to
> run page reclaim here.
This is the big question with this patch. How incestuous do I want to
get with the VM system in order to get it to free up pages? For now,
I decided to be fairly hands-off, allocate as many pages as I can get,
and return the total number to the host. The host, if it wasn't happy
with the results, can wait a bit while the UML notices that it is
really low on memory and frees some up, and then hit up the UML for
the remainder.
> > + char buf[sizeof("18446744073709551615\0")];
>
> rofl. We really ought to have a #define for "this architecture's maximum
> length of an asciified int/long/s32/s64". Generally people do
> guess-and-giggle-plus-20%, or they just get it wrong.
I can write one up. I did some quick grepping, and there are a good
number of constant over-estimates, plus some which might be in danger
with an large number of devices, plus one (kallsyms.c) which actually
does some sane-looking approximate math to get a reasonable number (which
is then doubled).
> * NOTE: Currently, only shmfs/tmpfs is supported for this operation.
> * Other filesystems return -ENOSYS.
>
> Are you expecting that this memory is backed by tmpfs?
Yes, but there should be some checking of this beforehand.
Drop this version for now, and I'll send a new one to cover these
problems plus the one that BlaisorBlade pointed out.
Jeff
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