From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757711Ab3J1XIS (ORCPT ); Mon, 28 Oct 2013 19:08:18 -0400 Received: from [204.155.152.216] ([204.155.152.216]:45599 "EHLO shutemov.name" rhost-flags-FAIL-FAIL-OK-OK) by vger.kernel.org with ESMTP id S1757233Ab3J1XIR (ORCPT ); Mon, 28 Oct 2013 19:08:17 -0400 Date: Tue, 29 Oct 2013 00:11:26 +0200 From: "Kirill A. Shutemov" 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 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> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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