On Thu, Sep 20, 2012 at 08:51:56AM +0900, Minchan Kim wrote:
> From: Minchan Kim <minchan@xxxxxxxxxx>
> Date: Thu, 20 Sep 2012 08:39:52 +0900
> Subject: [PATCH] mm: revert 0def08e3, mm/mempolicy.c: check return code of
> check_range
>
> This patch reverts 0def08e3 because check_range can't fail in
> migrate_to_node with considering current usecases.
>
> Quote from Johannes
> "
> I think it makes sense to revert. Not because of the semantics, but I
> just don't see how check_range() could even fail for this callsite:
>
> 1. we pass mm->mmap->vm_start in there, so we should not fail due to
> find_vma()
>
> 2. we pass MPOL_MF_DISCONTIG_OK, so the discontig checks do not apply
> and so can not fail
>
> 3. we pass MPOL_MF_MOVE | MPOL_MF_MOVE_ALL, the page table loops will
> continue until addr == end, so we never fail with -EIO
> "
>
> And I add new VM_BUG_ON for checking migrate_to_node's future usecase
> which might pass to MPOL_MF_STRICT.
>
> Cc: KOSAKI Motohiro <kosaki.motohiro@xxxxxxxxxxxxxx>
> Cc: Mel Gorman <mgorman@xxxxxxx>
> Cc: Christoph Lameter <cl@xxxxxxxxx>
> Cc: David Rientjes <rientjes@xxxxxxxxxx>
> Cc: Vasiliy Kulikov <segooon@xxxxxxxxx>
> Suggested-by: Johannes Weiner <hannes@xxxxxxxxxxx>
> Signed-off-by: Minchan Kim <minchan@xxxxxxxxxx>
> ---
> mm/mempolicy.c | 9 +++++----
> 1 file changed, 5 insertions(+), 4 deletions(-)
>
> diff --git a/mm/mempolicy.c b/mm/mempolicy.c
> index 3d64b36..9ec87bd 100644
> --- a/mm/mempolicy.c
> +++ b/mm/mempolicy.c
> @@ -946,15 +946,16 @@ static int migrate_to_node(struct mm_struct *mm, int source, int dest,
> nodemask_t nmask;
> LIST_HEAD(pagelist);
> int err = 0;
> - struct vm_area_struct *vma;
>
> nodes_clear(nmask);
> node_set(source, nmask);
>
> - vma = check_range(mm, mm->mmap->vm_start, mm->task_size, &nmask,
> + /*
> + * Collect migrate pages and it shoudn't be failed.
> + */
> + VM_BUG_ON(flags & MPOL_MF_STRICT);
Adding a check and a comment is a good idea, but I'm not a big fan of
checking for MPOL_MF_STRICT in particular because it's one of the
invalid inputs, and so you need to extend this check when somebody
extends the spectrum of invalid inputs. I would much prefer checking
directly for !(flags & (MPOL_MF_MOVE | MPOL_MF_MOVE_ALL)) instead, which
would also make the possible inputs apparent without having to chase
up the call chain to find out what is usually passed in.
And how about
/*
* This does not "check" the range but isolates all pages that
* need migration. Between passing in the full user address
* space range and MPOL_MF_DISCONTIG_OK, this call can not fail.
*/
?
> + check_range(mm, mm->mmap->vm_start, mm->task_size, &nmask,
> flags | MPOL_MF_DISCONTIG_OK, &pagelist);
> - if (IS_ERR(vma))
> - return PTR_ERR(vma);
>
> if (!list_empty(&pagelist)) {
> err = migrate_pages(&pagelist, new_node_page, dest,
> --
> 1.7.9.5
>
> --
> Kind regards,
> Minchan Kim
--
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>