Date: Sat, 19 Jul 2003 01:12:30 +0200
From: Andrea Arcangeli <andrea@suse.de>
To: William Lee Irwin III <wli@holomorphy.com>,
       Christoph Hellwig <hch@infradead.org>, linux-kernel@vger.kernel.org
Subject: Re: 2.4.22pre6aa1
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On Fri, Jul 18, 2003 at 04:04:31PM -0700, William Lee Irwin III wrote:
> On Sat, Jul 19, 2003 at 12:53:28AM +0200, Andrea Arcangeli wrote:
> > I tend to think the creation/destruction will be the most noticeable
> > performance difference in practice. allocating 42G in a single block
> > will take a bit of time ;). I'm not necessairly worse or unacceptable,
> > but it's different. And I feel I've to retain the bigpages= API (as an
> > API not as in implementation) anyways. Furthmore I'm unsure if hugtlbfs
> > is relaxed like the shm-largpeage patch is, I mean, it should be
> > possible to mmap the stuff with 4k granularty too, or stuff could break
> > due that change of API too.
> 
> I've just not gotten feedback about creation and destruction; I get the
> impression it's an uncommon operation.

It's uncommon of course. A 42G allocated all at once, may take a while
and 48G works flawlessy at peak performance w/o 4:4.  I support as much
as 64G all in a single shmfs file backed by bigpages (and it won't run
out of memory with a 64G box either, even with the 3:1 mapping)

> The alignment etc. considerations are bits I probably can't get merged. =(

so the apps will need changes and a kernel API way to know the hardware
page size provided by hugetlbfs (though they could probe for it with
many tries).

> Most of the work I did was trying to get the preexisting semantics into
> more standard-looking API's, e.g. vfs ops and standard-ish sysv shm.

yes.

Andrea
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