lkml.org 
[lkml]   [2010]   [Jul]   [7]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
DateWed, 7 Jul 2010 15:40:56 +0900
FromNaoya Horiguchi <>
SubjectRe: [PATCH 5/7] hugetlb: pin oldpage in page migration
Hi,

Thank you for your reviewing.

On Tue, Jul 06, 2010 at 10:54:38AM -0500, Christoph Lameter wrote:
> On Fri, 2 Jul 2010, Naoya Horiguchi wrote:
>
> > This patch introduces pinning the old page during page migration
> > to avoid freeing it before we complete copying.
>
> The old page is already pinned due to the reference count that is taken
> when the page is put onto the list of pages to be migrated. See
> do_move_pages() f.e.

OK.

> Huge pages use a different scheme?

Different scheme is in soft offline, where the target page is not pinned
before migration. So I should have pinned in soft offline side.
I'll fix it.

> > This race condition can happen for privately mapped or anonymous hugepage.
>
> It cannot happen unless you come up with your own scheme of managing pages
> to be migrated and bypass migrate_pages(). There you should take the
> refcount.

Yes.

> > /*
> > + * It's reasonable to pin the old page until unmapping and copying
> > + * complete, because when the original page is an anonymous hugepage,
> > + * it will be freed in try_to_unmap() due to the fact that
> > + * all references of anonymous hugepage come from mapcount.
> > + * Although in the other cases no problem comes out without pinning,
> > + * it looks logically correct to do it.
> > + */
> > + get_page(page);
> > +
> > + /*
>
> Its already pinned. Dont do this. migrate_pages() relies on the caller
> having pinned the page already.

I agree.

Thanks,
Naoya Horiguchi


\
 
 \ /
  Last update: 2010-07-07 08:49    [from the cache]
©2003-2010