Re: [PATCH] NOMMU: Separate out VMAs

Bernd Schmidt
2007-08-07T13:38:01Z

David Howells wrote:

> + /* we allocated a power-of-2 sized page set, so we need to trim off the
> + * excess */
> + total = 1 << order;
> + atomic_add(total, &mmap_pages_allocated);
> +
> + point = len >> PAGE_SHIFT;
> + while (point < total) {
> + order = ilog2(total - point);
> + _debug("shave %u/%lu", 1 << order, total - point);
> + atomic_sub(1 << order, &mmap_pages_allocated);
> + __free_pages(pages + point, order);
> + point += 1 << order;
> + }

Note that we've had a similar change in our kernel, and we've had to
revert it since the effect on fragmentation is just horrendous. Without
this, we could run a complete gcc testsuite on the board; with it we'd
run out of high-order pages somewhere in the middle.

This probably wants to be dependent on something like MAP_TRIM_EXCESS.

Bernd
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