From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752230Ab2EDH1a (ORCPT ); Fri, 4 May 2012 03:27:30 -0400 Received: from mga03.intel.com ([143.182.124.21]:51320 "EHLO mga03.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751039Ab2EDH13 (ORCPT ); Fri, 4 May 2012 03:27:29 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="4.71,315,1320652800"; d="scan'208";a="96294896" Message-ID: <4FA38495.1020207@intel.com> Date: Fri, 04 May 2012 15:26:13 +0800 From: Alex Shi User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:9.0) Gecko/20111229 Thunderbird/9.0 MIME-Version: 1.0 To: Andrea Arcangeli CC: Andrew Morton , riel@redhat.com, mgorman@suse.de, linux-kernel@vger.kernel.org Subject: Re: [PATCH] THP: need is_vma_temporary_stack() when reference transparent_hugepage_enabled References: <1335594795-30876-1-git-send-email-alex.shi@intel.com> <20120430160520.4c1cc05c.akpm@linux-foundation.org> <4FA0A743.2070904@intel.com> <20120502175508.GC2410@redhat.com> <4FA1D7D9.1050402@intel.com> <20120503112530.GE2410@redhat.com> In-Reply-To: <20120503112530.GE2410@redhat.com> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 05/03/2012 07:25 PM, Andrea Arcangeli wrote: > Hi, > > On Thu, May 03, 2012 at 08:56:57AM +0800, Alex Shi wrote: >> >>> My preference would still be to remove the is_vma_temporary_stack and >>> use two vmas during mremap of execve, that would remove the "vma" >>> parameter from transparent_hugepage_enabled() but others prefers to >>> skip a vma allocation in execve and stick to is_vma_temporary_stack, >>> which is fair enough argument. >> >> >> Actually, current transparent_hugepage_enabled just means the vma is in >> THP enable ENV, the vma is just possibly has some large page, no grantee >> really has. But in lots situations, user wants to know if a vma or a >> part of memory really include a large page. not the possibility. >> >> So, it will be great to see a real large page checking function appearing. > > Well, to know if a VMA (or a memory range) really includes a THP, it'd > require to hold the page_table_lock and a loop on all pmds in the > range, but by the time you relase the lock things may have already > changed as split_huge_page can run at any time, madvise(MADV_DONTNEED) > too if you only hold the mmap_sem in read mode and the THP page > fault. In fact while holding the mmap_sem in read mode (the usual read > lock you need to take to lookup and stabilize the vma) a THP can be > freed and reallocated under it, and that's what pmd_trans_unstable is > about. Appreciate for explanation!