From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pd0-f181.google.com (mail-pd0-f181.google.com [209.85.192.181]) by kanga.kvack.org (Postfix) with ESMTP id AFE5B6B0031 for ; Mon, 28 Oct 2013 19:07:48 -0400 (EDT) Received: by mail-pd0-f181.google.com with SMTP id x10so3084134pdj.12 for ; Mon, 28 Oct 2013 16:07:48 -0700 (PDT) Received: from psmtp.com ([74.125.245.112]) by mx.google.com with SMTP id cj2si13270215pbc.57.2013.10.28.16.07.46 for ; Mon, 28 Oct 2013 16:07:47 -0700 (PDT) Date: Tue, 29 Oct 2013 00:11:26 +0200 From: "Kirill A. Shutemov" Subject: Re: [PATCH 2/2] mm: thp: give transparent hugepage code a separate copy_page Message-ID: <20131028221126.GA29431@shutemov.name> References: <20131028221618.4078637F@viggo.jf.intel.com> <20131028221620.042323B3@viggo.jf.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20131028221620.042323B3@viggo.jf.intel.com> Sender: owner-linux-mm@kvack.org List-ID: To: Dave Hansen Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, dave.jiang@intel.com, Mel Gorman , akpm@linux-foundation.org, dhillf@gmail.com On Mon, Oct 28, 2013 at 03:16:20PM -0700, Dave Hansen wrote: > > From: Dave Hansen > > Right now, the migration code in migrate_page_copy() uses > copy_huge_page() for hugetlbfs and thp pages: > > if (PageHuge(page) || PageTransHuge(page)) > copy_huge_page(newpage, page); > > So, yay for code reuse. But: > > void copy_huge_page(struct page *dst, struct page *src) > { > struct hstate *h = page_hstate(src); > > and a non-hugetlbfs page has no page_hstate(). This > works 99% of the time because page_hstate() determines > the hstate from the page order alone. Since the page > order of a THP page matches the default hugetlbfs page > order, it works. > > But, if you change the default huge page size on the > boot command-line (say default_hugepagesz=1G), then > we might not even *have* a 2MB hstate so page_hstate() > returns null and copy_huge_page() oopses pretty fast > since copy_huge_page() dereferences the hstate: > > void copy_huge_page(struct page *dst, struct page *src) > { > struct hstate *h = page_hstate(src); > if (unlikely(pages_per_huge_page(h) > MAX_ORDER_NR_PAGES)) { > ... > > This patch creates a copy_high_order_page() which can > be used on THP pages. We already have copy_user_huge_page() and copy_user_gigantic_page() in generic code (mm/memory.c). I think copy_gigantic_page() and copy_huge_page() should be moved there too. BTW, I think pages_per_huge_page in copy_user_huge_page() is redunand: compound_order(page) should be enough, right? -- Kirill A. Shutemov -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org