Re: [patch 06/18] hugetlb: multi hstate proc files

[Nick Piggin <npiggin@suse.de>]

On Fri, May 02, 2008 at 12:53:11PM -0700, Nishanth Aravamudan wrote:
> On 23.04.2008 [11:53:08 +1000], npiggin@suse.de wrote:
> > Convert /proc output code over to report multiple hstates
> > 
> > I chose to just report the numbers in a row, in the hope 
> > to minimze breakage of existing software. The "compat" page size
> > is always the first number.
> 
> Only if add_huge_hstate() is called first for the compat page size,
> right? That seems bad if we depend on an ordering.
> 
> For instance, for power, I think Jon is calling huge_add_hstate() from
> the arch/powerpc/mm/hugetlbpage.c init routine. Which runs before
> hugetlb_init, which means that if he adds hugepages like
> 
> huge_add_hstate(64k-order);
> huge_add_hstate(16m-order);
> huge_add_hstate(16g-order);
> 
> We'll get 64k as the first field in meminfo.
> 
> So perhaps what we should do is:
> 
> 1) architectures define HPAGE_* as the default (compat) hugepage values
> 2) architectures have a call into generic code at their init time to
> specify what sizes they support
> 3) the core is the only place that actually does huge_add_hstate() and
> it always does it first for the compat order?
> 
> I wonder if this might lead to issues in timing between processing
> hugepagesz= (in arch code) and hugepages= (in generic code). Not sure. I
> guess if we always add all hugepage sizes, we should have all the
> hstates we know about ready to configure and as long as hugetlb_init
> runs before hugepages= processing, we should be fine? Dunno.

You're right I think. The other thing is that we could just have
a small map from the hstate array to reporting order for sysctls.
We could report them in the order specified on the cmdline, with
the default size first if it was not specified on the cmdline.

Hmm, I'll see how that looks.

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