Re: page migration: Fail with error if swap not setup

Andrew Morton
2006-03-15T03:24:43Z

Christoph Lameter <clameter@sgi.com> wrote:
>
> Currently the migration of anonymous pages will silently fail if no swap
> is setup.

Why?

I mean, if something tries to allocate a swap page and that fails then the
error should be propagated back. That's race-free.

> This patch makes page migration functions check for available
> swap and fail with -ENODEV if no swap space is available.
>
> Signed-off-by: Christoph Lameter <clameter@sgi.com>
>
> Index: linux-2.6.16-rc6/mm/mempolicy.c
> ===================================================================
> --- linux-2.6.16-rc6.orig/mm/mempolicy.c 2006-03-14 16:31:15.000000000 -0800
> +++ linux-2.6.16-rc6/mm/mempolicy.c 2006-03-14 17:25:09.000000000 -0800
> @@ -330,9 +330,14 @@ check_range(struct mm_struct *mm, unsign
> int err;
> struct vm_area_struct *first, *vma, *prev;
>
> - /* Clear the LRU lists so pages can be isolated */
> - if (flags & (MPOL_MF_MOVE | MPOL_MF_MOVE_ALL))
> + if (flags & (MPOL_MF_MOVE | MPOL_MF_MOVE_ALL)) {
> + /* Must have available swap entries for migration */
> + if (nr_swap_pages <=0)

(ObCodingStyleWhine)

> + return ERR_PTR(-ENODEV);
> +
> + /* Clear the LRU lists so pages can be isolated */
> lru_add_drain_all();
> + }
>

Whereas this appears to be racy...