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Date: Wed, 7 Jul 2010 15:40:56 +0900 From: Naoya Horiguchi <n-horiguchi@...jp.nec.com> To: Christoph Lameter <cl@...ux-foundation.org> Cc: Andi Kleen <andi@...stfloor.org>, Andrew Morton <akpm@...ux-foundation.org>, Mel Gorman <mel@....ul.ie>, Wu Fengguang <fengguang.wu@...el.com>, "Jun'ichi Nomura" <j-nomura@...jp.nec.com>, linux-mm <linux-mm@...ck.org>, LKML <linux-kernel@...r.kernel.org> Subject: Re: [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 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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