Re: [PATCH] NOMMU: Separate out VMAs

[Bernd Schmidt <bernds_cb1@t-online.de>]

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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