Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752756AbdFPOxm (ORCPT ); Fri, 16 Jun 2017 10:53:42 -0400 Received: from LGEAMRELO13.lge.com ([156.147.23.53]:58827 "EHLO lgeamrelo13.lge.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752321AbdFPOxl (ORCPT ); Fri, 16 Jun 2017 10:53:41 -0400 X-Original-SENDERIP: 156.147.1.151 X-Original-MAILFROM: minchan@kernel.org X-Original-SENDERIP: 10.177.220.163 X-Original-MAILFROM: minchan@kernel.org Date: Fri, 16 Jun 2017 23:53:33 +0900 From: Minchan Kim To: Andrea Arcangeli Cc: "Kirill A. Shutemov" , "Kirill A. Shutemov" , Andrew Morton , Vlastimil Babka , Vineet Gupta , Russell King , Will Deacon , Catalin Marinas , Ralf Baechle , "David S. Miller" , "Aneesh Kumar K . V" , Martin Schwidefsky , Heiko Carstens , linux-arch@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCHv2 3/3] mm: Use updated pmdp_invalidate() inteface to track dirty/accessed bits Message-ID: <20170616145333.GA29802@bbox> References: <20170615145224.66200-1-kirill.shutemov@linux.intel.com> <20170615145224.66200-4-kirill.shutemov@linux.intel.com> <20170616030250.GA27637@bbox> <20170616131908.3rxtm2w73gdfex4a@node.shutemov.name> <20170616135209.GA29542@bbox> <20170616142720.GH11676@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20170616142720.GH11676@redhat.com> User-Agent: Mutt/1.5.24 (2015-08-30) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1983 Lines: 45 Hi Andrea, On Fri, Jun 16, 2017 at 04:27:20PM +0200, Andrea Arcangeli wrote: > Hello Minchan, > > On Fri, Jun 16, 2017 at 10:52:09PM +0900, Minchan Kim wrote: > > > > > @@ -1995,8 +1984,6 @@ static void __split_huge_pmd_locked(struct vm_area_struct *vma, pmd_t *pmd, > > > > > if (soft_dirty) > > > > > entry = pte_mksoft_dirty(entry); > > > > > } > > > > > - if (dirty) > > > > > - SetPageDirty(page + i); > > > > > pte = pte_offset_map(&_pmd, addr); > [..] > > > > split_huge_page set PG_dirty to all subpages unconditionally? > > If it's true, yes, it doesn't break MADV_FREE. However, I didn't spot > > that piece of code. What I found one is just __split_huge_page_tail > > which set PG_dirty to subpage if head page is dirty. IOW, if the head > > page is not dirty, tail page will be clean, too. > > Could you point out what routine set PG_dirty to all subpages unconditionally? > > On a side note the snippet deleted above was useless, as long as > there's one left hugepmd to split, the physical page has to be still > compound and huge and as long as that's the case the tail pages > PG_dirty bit is meaningless (even if set, it's going to be clobbered > during the physical split). I got it during reviewing this patch. That's why I didn't argue this patch would break MADV_FREE by deleting routine which propagate dirty to pte of subpages. However, although it's useless, I prefer not removing the transfer of dirty bit. Because it would help MADV_FREE users who want to use smaps to know how many of pages are not freeable (i.e, dirtied) since MADV_FREE although it is not 100% correct. > > In short PG_dirty is only meaningful in the head as long as it's > compound. The physical split in __split_huge_page_tail transfer the > head value to the tails like you mentioned, that's all as far as I can > tell. Thanks for the comment. Then, this patch is to fix MADV_FREE's bug which has lost dirty bit by transferring dirty bit too early. Thanks.