Messages in this thread | | | Date | Thu, 23 Feb 2012 13:50:07 -0800 | From | Andrew Morton <> | Subject | Re: [PATCH -mm 1/2] mm: fix quadratic behaviour in get_unmapped_area_topdown |
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On Thu, 23 Feb 2012 14:56:36 -0500 Rik van Riel <riel@redhat.com> 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.
This has been at least partially addressed in recent patches from Xiao Guangrong. Please review his five-patch series starting with "[PATCH 1/5] hugetlbfs: fix hugetlb_get_unmapped_area".
I've already merged those patches and we need to work out what way to go.
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