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 -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxxx For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>