On Thu, Feb 23, 2012 at 02:56:36PM -0500, Rik van Riel wrote:

When we look for a VMA smaller than the cached_hole_size, we set the
starting search address to mm->mmap_base, to try and find our hole.

However, even in the case where we fall through and found nothing at
the mm->free_area_cache, we still reset the search address to mm->mmap_base.
This bug results in quadratic behaviour, with observed mmap times of 0.4
seconds for processes that have very fragmented memory.

If there is no hole small enough for us to fit the VMA, and we have
no good spot for us right at mm->free_area_cache, we are much better
off continuing the search down from mm->free_area_cache, instead of
all the way from the top.

Would it make sense to retain the restart for the case where we _know_
that the remaining address space can not fit the desired area?

	/* make sure it can fit in the remaining address space */
	if (addr > len) {
		vma = find_vma(mm, addr-len);
		if (!vma || addr <= vma->vm_start)
			/* remember the address as a hint for next time */
			return (mm->free_area_cache = addr-len);
	} else /* like this */
		addr = mm->mmap_base - len;

It would save one pointless find_vma() further down.  I don't feel too
strongly about it, though.  Either way:

Signed-off-by: Rik van Riel <redacted>

Acked-by: Johannes Weiner <hannes@cmpxchg.org>

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