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Date:   Mon, 12 Aug 2019 13:46:33 -0700
From:   Ira Weiny <ira.weiny@...el.com>
To:     John Hubbard <jhubbard@...dia.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Jason Gunthorpe <jgg@...pe.ca>,
        Dan Williams <dan.j.williams@...el.com>,
        Matthew Wilcox <willy@...radead.org>, Jan Kara <jack@...e.cz>,
        Theodore Ts'o <tytso@....edu>, Michal Hocko <mhocko@...e.com>,
        Dave Chinner <david@...morbit.com>, linux-xfs@...r.kernel.org,
        linux-rdma@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-fsdevel@...r.kernel.org, linux-nvdimm@...ts.01.org,
        linux-ext4@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [RFC PATCH v2 12/19] mm/gup: Prep put_user_pages() to take an
 vaddr_pin struct

On Fri, Aug 09, 2019 at 05:30:00PM -0700, John Hubbard wrote:
> On 8/9/19 3:58 PM, ira.weiny@...el.com wrote:
> > From: Ira Weiny <ira.weiny@...el.com>
> > 
> > Once callers start to use vaddr_pin the put_user_pages calls will need
> > to have access to this data coming in.  Prep put_user_pages() for this
> > data.
> > 
> > Signed-off-by: Ira Weiny <ira.weiny@...el.com>

[snip]

> > diff --git a/mm/gup.c b/mm/gup.c
> > index a7a9d2f5278c..10cfd30ff668 100644
> > --- a/mm/gup.c
> > +++ b/mm/gup.c
> > @@ -24,30 +24,41 @@
> >  
> >  #include "internal.h"
> >  
> > -/**
> > - * put_user_pages_dirty_lock() - release and optionally dirty gup-pinned pages
> > - * @pages:  array of pages to be maybe marked dirty, and definitely released.
> 
> A couple comments from our circular review chain: some fellow with the same
> last name as you, recommended wording it like this:
> 
>       @pages:  array of pages to be put

Sure, see below...

> 
> > - * @npages: number of pages in the @pages array.
> > - * @make_dirty: whether to mark the pages dirty
> > - *
> > - * "gup-pinned page" refers to a page that has had one of the get_user_pages()
> > - * variants called on that page.
> > - *
> > - * For each page in the @pages array, make that page (or its head page, if a
> > - * compound page) dirty, if @make_dirty is true, and if the page was previously
> > - * listed as clean. In any case, releases all pages using put_user_page(),
> > - * possibly via put_user_pages(), for the non-dirty case.
> > - *
> > - * Please see the put_user_page() documentation for details.
> > - *
> > - * set_page_dirty_lock() is used internally. If instead, set_page_dirty() is
> > - * required, then the caller should a) verify that this is really correct,
> > - * because _lock() is usually required, and b) hand code it:
> > - * set_page_dirty_lock(), put_user_page().
> > - *
> > - */
> > -void put_user_pages_dirty_lock(struct page **pages, unsigned long npages,
> > -			       bool make_dirty)
> > +static void __put_user_page(struct vaddr_pin *vaddr_pin, struct page *page)
> > +{
> > +	page = compound_head(page);
> > +
> > +	/*
> > +	 * For devmap managed pages we need to catch refcount transition from
> > +	 * GUP_PIN_COUNTING_BIAS to 1, when refcount reach one it means the
> > +	 * page is free and we need to inform the device driver through
> > +	 * callback. See include/linux/memremap.h and HMM for details.
> > +	 */
> > +	if (put_devmap_managed_page(page))
> > +		return;
> > +
> > +	if (put_page_testzero(page))
> > +		__put_page(page);
> > +}
> > +
> > +static void __put_user_pages(struct vaddr_pin *vaddr_pin, struct page **pages,
> > +			     unsigned long npages)
> > +{
> > +	unsigned long index;
> > +
> > +	/*
> > +	 * TODO: this can be optimized for huge pages: if a series of pages is
> > +	 * physically contiguous and part of the same compound page, then a
> > +	 * single operation to the head page should suffice.
> > +	 */
> 
> As discussed in the other review thread (""), let's just delete that comment,
> as long as you're moving things around.

Done.

> 
> 
> > +	for (index = 0; index < npages; index++)
> > +		__put_user_page(vaddr_pin, pages[index]);
> > +}
> > +
> > +static void __put_user_pages_dirty_lock(struct vaddr_pin *vaddr_pin,
> > +					struct page **pages,
> > +					unsigned long npages,
> > +					bool make_dirty)
> 
> Elsewhere in this series, we pass vaddr_pin at the end of the arg list.
> Here we pass it at the beginning, and it caused a minor jar when reading it.
> Obviously just bike shedding at this point, though. Either way. :)

Yea I guess that is odd...  I changed it.  Not a big deal.

> 
> >  {
> >  	unsigned long index;
> >  
> > @@ -58,7 +69,7 @@ void put_user_pages_dirty_lock(struct page **pages, unsigned long npages,
> >  	 */
> >  
> >  	if (!make_dirty) {
> > -		put_user_pages(pages, npages);
> > +		__put_user_pages(vaddr_pin, pages, npages);
> >  		return;
> >  	}
> >  
> > @@ -86,9 +97,58 @@ void put_user_pages_dirty_lock(struct page **pages, unsigned long npages,
> >  		 */
> >  		if (!PageDirty(page))
> >  			set_page_dirty_lock(page);
> > -		put_user_page(page);
> > +		__put_user_page(vaddr_pin, page);
> >  	}
> >  }
> > +
> > +/**
> > + * put_user_page() - release a gup-pinned page
> > + * @page:            pointer to page to be released
> > + *
> > + * Pages that were pinned via get_user_pages*() must be released via
> > + * either put_user_page(), or one of the put_user_pages*() routines
> > + * below. This is so that eventually, pages that are pinned via
> > + * get_user_pages*() can be separately tracked and uniquely handled. In
> > + * particular, interactions with RDMA and filesystems need special
> > + * handling.
> > + *
> > + * put_user_page() and put_page() are not interchangeable, despite this early
> > + * implementation that makes them look the same. put_user_page() calls must
> > + * be perfectly matched up with get_user_page() calls.
> > + */
> > +void put_user_page(struct page *page)
> > +{
> > +	__put_user_page(NULL, page);
> > +}
> > +EXPORT_SYMBOL(put_user_page);
> > +
> > +/**
> > + * put_user_pages_dirty_lock() - release and optionally dirty gup-pinned pages
> > + * @pages:  array of pages to be maybe marked dirty, and definitely released.
> 
> Same here:
> 
>       @pages:  array of pages to be put

Actually here is the only place.  Above was removing the text to be put here...

Done -- I'll made a lead in patch because this was just copied text.

> 
> > + * @npages: number of pages in the @pages array.
> > + * @make_dirty: whether to mark the pages dirty
> > + *
> > + * "gup-pinned page" refers to a page that has had one of the get_user_pages()
> > + * variants called on that page.
> > + *
> > + * For each page in the @pages array, make that page (or its head page, if a
> > + * compound page) dirty, if @make_dirty is true, and if the page was previously
> > + * listed as clean. In any case, releases all pages using put_user_page(),
> > + * possibly via put_user_pages(), for the non-dirty case.
> > + *
> > + * Please see the put_user_page() documentation for details.
> > + *
> > + * set_page_dirty_lock() is used internally. If instead, set_page_dirty() is
> > + * required, then the caller should a) verify that this is really correct,
> > + * because _lock() is usually required, and b) hand code it:
> > + * set_page_dirty_lock(), put_user_page().
> > + *
> > + */
> > +void put_user_pages_dirty_lock(struct page **pages, unsigned long npages,
> > +			       bool make_dirty)
> > +{
> > +	__put_user_pages_dirty_lock(NULL, pages, npages, make_dirty);
> > +}
> >  EXPORT_SYMBOL(put_user_pages_dirty_lock);
> >  
> >  /**
> > @@ -102,15 +162,7 @@ EXPORT_SYMBOL(put_user_pages_dirty_lock);
> >   */
> >  void put_user_pages(struct page **pages, unsigned long npages)
> >  {
> > -	unsigned long index;
> > -
> > -	/*
> > -	 * TODO: this can be optimized for huge pages: if a series of pages is
> > -	 * physically contiguous and part of the same compound page, then a
> > -	 * single operation to the head page should suffice.
> > -	 */
> > -	for (index = 0; index < npages; index++)
> > -		put_user_page(pages[index]);
> > +	__put_user_pages(NULL, pages, npages);
> >  }
> >  EXPORT_SYMBOL(put_user_pages);
> >  
> > 
> 
> This all looks pretty good, so regardless of the outcome of the minor
> points above,
>    
>     Reviewed-by: John Hubbard <jhubbard@...dia.com>

Thanks,
Ira

> 
> 
> thanks,
> -- 
> John Hubbard
> NVIDIA

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