From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752045Ab2KFJPa (ORCPT ); Tue, 6 Nov 2012 04:15:30 -0500 Received: from cantor2.suse.de ([195.135.220.15]:36280 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751397Ab2KFJPG (ORCPT ); Tue, 6 Nov 2012 04:15:06 -0500 From: Mel Gorman To: Peter Zijlstra , Andrea Arcangeli , Ingo Molnar Cc: Rik van Riel , Johannes Weiner , Hugh Dickins , Thomas Gleixner , Linus Torvalds , Andrew Morton , Linux-MM , LKML , Mel Gorman Subject: [PATCH 06/19] mm: numa: teach gup_fast about pmd_numa Date: Tue, 6 Nov 2012 09:14:42 +0000 Message-Id: <1352193295-26815-7-git-send-email-mgorman@suse.de> X-Mailer: git-send-email 1.7.9.2 In-Reply-To: <1352193295-26815-1-git-send-email-mgorman@suse.de> References: <1352193295-26815-1-git-send-email-mgorman@suse.de> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Andrea Arcangeli When scanning pmds, the pmd may be of numa type (_PAGE_PRESENT not set), however the pte might be present. Therefore, gup_pmd_range() must return 0 in this case to avoid losing a NUMA hinting page fault during gup_fast. Note: gup_fast will skip over non present ptes (like numa types), so no explicit check is needed for the pte_numa case. gup_fast will also skip over THP when the trans huge pmd is non present. So, the pmd_numa case will also be correctly skipped with no additional code changes required. Acked-by: Rik van Riel Signed-off-by: Andrea Arcangeli Signed-off-by: Mel Gorman --- arch/x86/mm/gup.c | 13 ++++++++++++- 1 file changed, 12 insertions(+), 1 deletion(-) diff --git a/arch/x86/mm/gup.c b/arch/x86/mm/gup.c index dd74e46..02c5ec5 100644 --- a/arch/x86/mm/gup.c +++ b/arch/x86/mm/gup.c @@ -163,8 +163,19 @@ static int gup_pmd_range(pud_t pud, unsigned long addr, unsigned long end, * can't because it has irq disabled and * wait_split_huge_page() would never return as the * tlb flush IPI wouldn't run. + * + * The pmd_numa() check is needed because the code + * doesn't check the _PAGE_PRESENT bit of the pmd if + * the gup_pte_range() path is taken. NOTE: not all + * gup_fast users will will access the page contents + * using the CPU through the NUMA memory channels like + * KVM does. So we're forced to trigger NUMA hinting + * page faults unconditionally for all gup_fast users + * even though NUMA hinting page faults aren't useful + * to I/O drivers that will access the page with DMA + * and not with the CPU. */ - if (pmd_none(pmd) || pmd_trans_splitting(pmd)) + if (pmd_none(pmd) || pmd_trans_splitting(pmd) || pmd_numa(pmd)) return 0; if (unlikely(pmd_large(pmd))) { if (!gup_huge_pmd(pmd, addr, next, write, pages, nr)) -- 1.7.9.2