From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-lf0-f69.google.com (mail-lf0-f69.google.com [209.85.215.69]) by kanga.kvack.org (Postfix) with ESMTP id 27CCE6B0038 for ; Tue, 18 Oct 2016 06:50:05 -0400 (EDT) Received: by mail-lf0-f69.google.com with SMTP id i187so8759636lfe.4 for ; Tue, 18 Oct 2016 03:50:05 -0700 (PDT) Received: from mx2.suse.de (mx2.suse.de. [195.135.220.15]) by mx.google.com with ESMTPS id z17si48032798wjw.26.2016.10.18.03.50.03 for (version=TLS1 cipher=AES128-SHA bits=128/128); Tue, 18 Oct 2016 03:50:03 -0700 (PDT) Date: Tue, 18 Oct 2016 12:50:00 +0200 From: Jan Kara Subject: Re: [PATCH 12/20] mm: Factor out common parts of write fault handling Message-ID: <20161018105000.GQ3359@quack2.suse.cz> References: <1474992504-20133-1-git-send-email-jack@suse.cz> <1474992504-20133-13-git-send-email-jack@suse.cz> <20161017220851.GA26960@linux.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20161017220851.GA26960@linux.intel.com> Sender: owner-linux-mm@kvack.org List-ID: To: Ross Zwisler Cc: Jan Kara , linux-mm@kvack.org, linux-fsdevel@vger.kernel.org, linux-nvdimm@lists.01.org, Dan Williams , "Kirill A. Shutemov" On Mon 17-10-16 16:08:51, Ross Zwisler wrote: > On Tue, Sep 27, 2016 at 06:08:16PM +0200, Jan Kara wrote: > > Currently we duplicate handling of shared write faults in > > wp_page_reuse() and do_shared_fault(). Factor them out into a common > > function. > > > > Signed-off-by: Jan Kara > > --- > > mm/memory.c | 78 +++++++++++++++++++++++++++++-------------------------------- > > 1 file changed, 37 insertions(+), 41 deletions(-) > > > > diff --git a/mm/memory.c b/mm/memory.c > > index 63d9c1a54caf..0643b3b5a12a 100644 > > --- a/mm/memory.c > > +++ b/mm/memory.c > > @@ -2063,6 +2063,41 @@ static int do_page_mkwrite(struct vm_area_struct *vma, struct page *page, > > } > > > > /* > > + * Handle dirtying of a page in shared file mapping on a write fault. > > + * > > + * The function expects the page to be locked and unlocks it. > > + */ > > +static void fault_dirty_shared_page(struct vm_area_struct *vma, > > + struct page *page) > > +{ > > + struct address_space *mapping; > > + bool dirtied; > > + bool page_mkwrite = vma->vm_ops->page_mkwrite; > > I think you may need to pass in a 'page_mkwrite' parameter if you don't want > to change behavior. Just checking to see of vma->vm_ops->page_mkwrite is > non-NULL works fine for this path: > > do_shared_fault() > fault_dirty_shared_page() > > and for > > wp_page_shared() > wp_page_reuse() > fault_dirty_shared_page() > > But for these paths: > > wp_pfn_shared() > wp_page_reuse() > fault_dirty_shared_page() > > and > > do_wp_page() > wp_page_reuse() > fault_dirty_shared_page() > > we unconditionally pass 0 for the 'page_mkwrite' parameter, even though from > the logic in wp_pfn_shared() especially you can see that > vma->vm_ops->pfn_mkwrite() must be defined some of the time. The trick which makes this work is that for fault_dirty_shared_page() to be called at all, you have to set 'dirty_shared' argument to wp_page_reuse() and that does not happen from wp_pfn_shared() and do_wp_page() paths. So things work as they should. If you look somewhat later into the series, the patch "mm: Move part of wp_page_reuse() into the single call site" cleans this up to make things more obvious. Honza -- Jan Kara SUSE Labs, CR -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org