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Date:   Fri, 9 Aug 2019 17:30:00 -0700
From:   John Hubbard <jhubbard@...dia.com>
To:     <ira.weiny@...el.com>, Andrew Morton <akpm@...ux-foundation.org>
CC:     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 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>
> ---
>  include/linux/mm.h |  20 +-------
>  mm/gup.c           | 122 ++++++++++++++++++++++++++++++++-------------
>  2 files changed, 88 insertions(+), 54 deletions(-)
> 
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index befe150d17be..9d37cafbef9a 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -1064,25 +1064,7 @@ static inline void put_page(struct page *page)
>  		__put_page(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.
> - */
> -static inline void put_user_page(struct page *page)
> -{
> -	put_page(page);
> -}
> +void put_user_page(struct page *page);
>  
>  void put_user_pages_dirty_lock(struct page **pages, unsigned long npages,
>  			       bool make_dirty);
> 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

> - * @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.


> +	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. :)

>  {
>  	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

> + * @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,
-- 
John Hubbard
NVIDIA

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