Re: Can't mlock hugetlb in 2.6.15

[Adam Litke <agl@us.ibm.com>]

Aye.

On Mon, 2006-01-23 at 19:51 +0000, Hugh Dickins wrote:
> Thanks a lot for the strace, that indeed helped to track it down.
> 
> This has nothing to do with mlock or MAP_LOCKED - which by the way do
> make more sense in 2.6.15, since they provide a way of prefaulting the
> hugepage area like in earlier releases (now hugepages are being faulted
> in on demand, though never paged out, as Andrew said).
> 
> Please try the patch below, and let us know if it works for you - thanks.
> Looks like we'll need this in 2.6.16-rc-git and 2.6.15-stable.
> 
> 
> 2.6.15's hugepage faulting introduced huge_pages_needed accounting into
> hugetlbfs: to count how many pages are already in cache, for spot check
> on how far a new mapping may be allowed to extend the file.  But it's
> muddled: each hugepage found covers HPAGE_SIZE, not PAGE_SIZE.  Once
> pages were already in cache, it would overshoot, wrap its hugepages
> count backwards, and so fail a harmless repeat mapping with -ENOMEM.
> Fixes the problem found by Don Dupuis.
> 
> Signed-off-by: Hugh Dickins <hugh@veritas.com>
Acked-By: Adam Litke <agl@us.ibm.com>
> ---
> 
>  fs/hugetlbfs/inode.c |    4 ++--
>  1 files changed, 2 insertions(+), 2 deletions(-)
> 
> --- 2.6.15/fs/hugetlbfs/inode.c	2006-01-03 03:21:10.000000000 +0000
> +++ linux/fs/hugetlbfs/inode.c	2006-01-23 18:39:47.000000000 +0000
> @@ -71,8 +71,8 @@ huge_pages_needed(struct address_space *
>  	unsigned long start = vma->vm_start;
>  	unsigned long end = vma->vm_end;
>  	unsigned long hugepages = (end - start) >> HPAGE_SHIFT;
> -	pgoff_t next = vma->vm_pgoff;
> -	pgoff_t endpg = next + ((end - start) >> PAGE_SHIFT);
> +	pgoff_t next = vma->vm_pgoff >> (HPAGE_SHIFT - PAGE_SHIFT);
> +	pgoff_t endpg = next + hugepages;
>  
>  	pagevec_init(&pvec, 0);
>  	while (next < endpg) {
> 
> 
-- 
Adam Litke - (agl at us.ibm.com)
IBM Linux Technology Center