Re: [PATCH 2/3] mm/mmu_notifier: use structure for invalidate_range_start/end calls

From: Jan Kara <jack@suse.cz>
To: Jerome Glisse <jglisse@redhat.com>
Cc: "Ralph Campbell" <rcampbell@nvidia.com>,
	"Jan Kara" <jack@suse.cz>,
	kvm@vger.kernel.org, "Matthew Wilcox" <mawilcox@microsoft.com>,
	linux-rdma@vger.kernel.org, "John Hubbard" <jhubbard@nvidia.com>,
	"Felix Kuehling" <felix.kuehling@amd.com>,
	"Radim Krčmář" <rkrcmar@redhat.com>,
	linux-kernel@vger.kernel.org, dri-devel@lists.freedesktop.org,
	"Michal Hocko" <mhocko@kernel.org>,
	linux-mm@kvack.org, "Christian Koenig" <christian.koenig@amd.com>,
	"Ross Zwisler" <zwisler@kernel.org>,
	linux-fsdevel@vger.kernel.org,
	"Paolo Bonzini" <pbonzini@redhat.com>,
	"Andrew Morton" <akpm@linux-foundation.org>,
	"Dan Williams" <dan.j.williams@intel.com>
Subject: Re: [PATCH 2/3] mm/mmu_notifier: use structure for invalidate_range_start/end calls
Date: Wed, 5 Dec 2018 17:28:57 +0100	[thread overview]
Message-ID: <20181205162857.GF30615@quack2.suse.cz> (raw)
In-Reply-To: <20181205155357.GA3536@redhat.com>

On Wed 05-12-18 10:53:57, Jerome Glisse wrote:
> On Wed, Dec 05, 2018 at 12:04:16PM +0100, Jan Kara wrote:
> > Hi Jerome!
> > 
> > On Mon 03-12-18 15:18:16, jglisse@redhat.com wrote:
> > > From: Jérôme Glisse <jglisse@redhat.com>
> > > 
> > > To avoid having to change many call sites everytime we want to add a
> > > parameter use a structure to group all parameters for the mmu_notifier
> > > invalidate_range_start/end cakks. No functional changes with this
> > > patch.
> > 
> > Two suggestions for the patch below:
> > 
> > > @@ -772,7 +775,8 @@ static void dax_entry_mkclean(struct address_space *mapping, pgoff_t index,
> > >  		 * call mmu_notifier_invalidate_range_start() on our behalf
> > >  		 * before taking any lock.
> > >  		 */
> > > -		if (follow_pte_pmd(vma->vm_mm, address, &start, &end, &ptep, &pmdp, &ptl))
> > > +		if (follow_pte_pmd(vma->vm_mm, address, &range,
> > > +				   &ptep, &pmdp, &ptl))
> > >  			continue;
> > 
> > The change of follow_pte_pmd() arguments looks unexpected. Why should that
> > care about mmu notifier range? I see it may be convenient but it doesn't look
> > like a good API to me.
> 
> Saddly i do not see a way around that one this is because of fs/dax.c
> which does the mmu_notifier_invalidate_range_end while follow_pte_pmd
> do the mmu_notifier_invalidate_range_start

I see so this is really a preexisting problem with follow_pte_pmd() having
ugly interface. After some thoughts I think your patch actually slightly
improves the situation so OK.

								Honza
-- 
Jan Kara <jack@suse.com>
SUSE Labs, CR
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