From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755568AbaEHVpd (ORCPT ); Thu, 8 May 2014 17:45:33 -0400 Received: from mail-pa0-f46.google.com ([209.85.220.46]:43954 "EHLO mail-pa0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754871AbaEHVpc (ORCPT ); Thu, 8 May 2014 17:45:32 -0400 Message-ID: <536BFAF7.4020405@linaro.org> Date: Thu, 08 May 2014 14:45:27 -0700 From: John Stultz User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:24.0) Gecko/20100101 Thunderbird/24.5.0 MIME-Version: 1.0 To: Minchan Kim CC: LKML , Andrew Morton , Android Kernel Team , Johannes Weiner , Robert Love , Mel Gorman , Hugh Dickins , Dave Hansen , Rik van Riel , Dmitry Adamushko , Neil Brown , Andrea Arcangeli , Mike Hommey , Taras Glek , Jan Kara , KOSAKI Motohiro , Michel Lespinasse , Keith Packard , "linux-mm@kvack.org" Subject: Re: [PATCH 3/4] MADV_VOLATILE: Add purged page detection on setting memory non-volatile References: <1398806483-19122-1-git-send-email-john.stultz@linaro.org> <1398806483-19122-4-git-send-email-john.stultz@linaro.org> <20140508015130.GB5282@bbox> In-Reply-To: <20140508015130.GB5282@bbox> X-Enigmail-Version: 1.6 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 05/07/2014 06:51 PM, Minchan Kim wrote: > On Tue, Apr 29, 2014 at 02:21:22PM -0700, John Stultz wrote: >> +/** >> + * mvolatile_check_purged_pte - Checks ptes for purged pages >> + * @pmd: pmd to walk >> + * @addr: starting address >> + * @end: end address >> + * @walk: mm_walk ptr (contains ptr to mvolatile_walker) >> + * >> + * Iterates over the ptes in the pmd checking if they have >> + * purged swap entries. >> + * >> + * Sets the mvolatile_walker.page_was_purged to 1 if any were purged, >> + * and clears the purged pte swp entries (since the pages are no >> + * longer volatile, we don't want future accesses to SIGBUS). >> + */ >> +static int mvolatile_check_purged_pte(pmd_t *pmd, unsigned long addr, >> + unsigned long end, struct mm_walk *walk) >> +{ >> + struct mvolatile_walker *vw = walk->private; >> + pte_t *pte; >> + spinlock_t *ptl; >> + >> + if (pmd_trans_huge(*pmd)) >> + return 0; >> + if (pmd_trans_unstable(pmd)) >> + return 0; >> + >> + pte = pte_offset_map_lock(walk->mm, pmd, addr, &ptl); >> + for (; addr != end; pte++, addr += PAGE_SIZE) { >> + if (!pte_present(*pte)) { >> + swp_entry_t mvolatile_entry = pte_to_swp_entry(*pte); >> + >> + if (unlikely(is_purged_entry(mvolatile_entry))) { >> + >> + vw->page_was_purged = 1; >> + >> + /* clear the pte swp entry */ >> + flush_cache_page(vw->vma, addr, pte_pfn(*pte)); > Maybe we don't need to flush the cache because there is no mapped page. > >> + ptep_clear_flush(vw->vma, addr, pte); > Maybe we don't need this, either. We didn't set present bit for purged > page but when I look at the internal of ptep_clear_flush, it checks present bit > and skip the TLB flush so it's okay for x86 but not sure other architecture. > More clear function for our purpose would be pte_clear_not_present_full. Ok.. basically I just wanted to zap the psudo-swp entry, so it will be zero-filled from here on out. > And we are changing page table so at least, we need to handle mmu_notifier to > inform that to the client of mmu_notifier. So yes, this is one item from my last iteration that I didn't act on yet. It wasn't clear to me here that we need to do the mmu_notifier, since the page is evicted earlier via try_to_purge_one (and we do notify then). But in just removing the psudo-swap entry we need to do a notification as well? Is there someplace where the mmu_notifier rules are better documented? thanks -john