On Wed 26-09-12 16:56:17, Johannes Weiner wrote: > On Mon, Aug 13, 2012 at 03:55:41PM +0200, Michal Hocko wrote: > > 0c176d5 (mm: hugetlb: fix pgoff computation when unmapping page > > from vma) fixed pgoff calculation but it has replaced it by > > vma_hugecache_offset which is not approapriate for offsets used for > > vma_prio_tree_foreach because that one expects index in page units > > rather than in huge_page_shift. > > Using vma_hugecache_offset is not incorrect because the pgoff will fit > > into the same vmas but it is confusing so the standard PAGE_SHIFT based > > index calculation is used instead. > > I do think it's incorrect. The resulting index may not be too big, > but it can be too small: assume hpage size of 2M and the address to > unmap to be 0x200000. This is regular page index 512 and hpage index > 1. If you have a VMA that maps the file only starting at the second > huge page, that VMAs vm_pgoff will be 512 but you ask for offset 1 and > miss it even though it does map the page of interest. hugetlb_cow() > will try to unmap, miss the vma, and retry the cow until the > allocation succeeds or the skipped vma(s) go away. > > Unless I missed something, this should not be deferred as a cleanup. You are right and I have totally missed this because I focused on the other boundary too much :/ This vma_hugecache_offset is really confusing. Andrew has already updated the changelog so we will not get even more confusion into the Linus tree. Thanks for spotting this Johannes! -- Michal Hocko SUSE Labs -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>