From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933266AbbFJHXT (ORCPT ); Wed, 10 Jun 2015 03:23:19 -0400 Received: from mail-la0-f46.google.com ([209.85.215.46]:36182 "EHLO mail-la0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754050AbbFJHXL (ORCPT ); Wed, 10 Jun 2015 03:23:11 -0400 Date: Wed, 10 Jun 2015 10:23:05 +0300 From: Cyrill Gorcunov To: Minchan Kim Cc: Andrew Morton , Hugh Dickins , Rik van Riel , Mel Gorman , Michal Hocko , Johannes Weiner , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Pavel Emelyanov , Yalin Wang Subject: Re: [RFC 3/6] mm: mark dirty bit on swapped-in page Message-ID: <20150610072305.GB13008@uranus> References: <1433312145-19386-1-git-send-email-minchan@kernel.org> <1433312145-19386-4-git-send-email-minchan@kernel.org> <20150609190737.GV13008@uranus> <20150609235206.GB12689@bgram> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20150609235206.GB12689@bgram> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Jun 10, 2015 at 08:52:06AM +0900, Minchan Kim wrote: > > > +++ b/mm/memory.c > > > @@ -2557,9 +2557,11 @@ static int do_swap_page(struct mm_struct *mm, struct vm_area_struct *vma, > > > > > > inc_mm_counter_fast(mm, MM_ANONPAGES); > > > dec_mm_counter_fast(mm, MM_SWAPENTS); > > > - pte = mk_pte(page, vma->vm_page_prot); > > > + > > > + /* Mark dirty bit of page table because MADV_FREE relies on it */ > > > + pte = pte_mkdirty(mk_pte(page, vma->vm_page_prot)); > > > if ((flags & FAULT_FLAG_WRITE) && reuse_swap_page(page)) { > > > - pte = maybe_mkwrite(pte_mkdirty(pte), vma); > > > + pte = maybe_mkwrite(pte, vma); > > > flags &= ~FAULT_FLAG_WRITE; > > > ret |= VM_FAULT_WRITE; > > > exclusive = 1; > > > > Hi Minchan! Really sorry for delay in reply. Look, I don't understand > > the moment -- if page has fault on read then before the patch the > > PTE won't carry the dirty flag but now we do set it up unconditionally > > and to me it looks somehow strange at least because this as well > > sets soft-dirty bit on pages which were not modified but only swapped > > out. Am I missing something obvious? > > It's same one I sent a while ago and you said it's okay at that time. ;-) Ah, I recall. If there is no way to escape dirtifying the page in pte itself maybe we should at least not make it softdirty on read faults? > Okay, It might be lack of description compared to one I sent long time ago > because I moved some part of description to another patch and I didn't Cc > you. Sorry. I hope below will remind you. > > https://www.mail-archive.com/linux-kernel%40vger.kernel.org/msg857827.html > > In summary, the problem is that in MADV_FREE point of view, > clean anonymous page(ie, no dirty) in page table entry has a problem > about sudden discarding under us by reclaimer. Otherwise, VM cannot > discard MADV_FREE hinted pages by PageDirty flag of page descriptor. > > This patchset aims for solving the problem. > Please feel free to ask if you have questions without wasting your time > unless you can remind after reading above URL > > Thanks for looking!