linux-kernel - Re: [PATCH 2/3] mm/mmu_notifier: use structure for invalidate_range

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Date:   Wed, 5 Dec 2018 17:28:57 +0100
From:   Jan Kara <jack@...e.cz>
To:     Jerome Glisse <jglisse@...hat.com>
Cc:     Jan Kara <jack@...e.cz>, linux-mm@...ck.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        linux-kernel@...r.kernel.org,
        Matthew Wilcox <mawilcox@...rosoft.com>,
        Ross Zwisler <zwisler@...nel.org>,
        Dan Williams <dan.j.williams@...el.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Radim Krčmář <rkrcmar@...hat.com>,
        Michal Hocko <mhocko@...nel.org>,
        Christian Koenig <christian.koenig@....com>,
        Felix Kuehling <felix.kuehling@....com>,
        Ralph Campbell <rcampbell@...dia.com>,
        John Hubbard <jhubbard@...dia.com>, kvm@...r.kernel.org,
        dri-devel@...ts.freedesktop.org, linux-rdma@...r.kernel.org,
        linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH 2/3] mm/mmu_notifier: use structure for
 invalidate_range_start/end calls

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@...hat.com wrote:
> > > From: Jérôme Glisse <jglisse@...hat.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@...e.com>
SUSE Labs, CR