Re: [PATCH v6 06/13] mm, dev_pagemap: Do not clear ->mapping on final put

[Jerome Glisse <jglisse@redhat.com>]

On Mon, Jul 23, 2018 at 09:12:06AM -0700, Dave Jiang wrote:
> Jerome,
> Is it possible to get an ack for this? Thanks!
> 
> On 07/13/2018 09:50 PM, Dan Williams wrote:
> > MEMORY_DEVICE_FS_DAX relies on typical page semantics whereby ->mapping
> > is only ever cleared by truncation, not final put.
> > 
> > Without this fix dax pages may forget their mapping association at the
> > end of every page pin event.
> > 
> > Move this atypical behavior that HMM wants into the HMM ->page_free()
> > callback.
> > 
> > Cc: <stable@vger.kernel.org>
> > Cc: Jan Kara <jack@suse.cz>
> > Cc: Andrew Morton <akpm@linux-foundation.org>
> > Cc: Ross Zwisler <ross.zwisler@linux.intel.com>
> > Fixes: d2c997c0f145 ("fs, dax: use page->mapping...")
> > Signed-off-by: Dan Williams <dan.j.williams@intel.com>

Acked-by: Jérôme Glisse <jglisse@redhat.com>

> > ---
> >  kernel/memremap.c |    1 -
> >  mm/hmm.c          |    2 ++
> >  2 files changed, 2 insertions(+), 1 deletion(-)
> > 
> > diff --git a/kernel/memremap.c b/kernel/memremap.c
> > index 5857267a4af5..62603634a1d2 100644
> > --- a/kernel/memremap.c
> > +++ b/kernel/memremap.c
> > @@ -339,7 +339,6 @@ void __put_devmap_managed_page(struct page *page)
> >  		__ClearPageActive(page);
> >  		__ClearPageWaiters(page);
> >  
> > -		page->mapping = NULL;
> >  		mem_cgroup_uncharge(page);
> >  
> >  		page->pgmap->page_free(page, page->pgmap->data);
> > diff --git a/mm/hmm.c b/mm/hmm.c
> > index de7b6bf77201..f9d1d89dec4d 100644
> > --- a/mm/hmm.c
> > +++ b/mm/hmm.c
> > @@ -963,6 +963,8 @@ static void hmm_devmem_free(struct page *page, void *data)
> >  {
> >  	struct hmm_devmem *devmem = data;
> >  
> > +	page->mapping = NULL;
> > +
> >  	devmem->ops->free(devmem, page);
> >  }
> >  
> > 
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> >