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From: Jerome Glisse <jglisse@redhat.com>
To: John Hubbard <jhubbard@nvidia.com>
Cc: "Andrew Morton" <akpm@linux-foundation.org>,
	"Al Viro" <viro@zeniv.linux.org.uk>,
	"Alex Williamson" <alex.williamson@redhat.com>,
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	LKML <linux-kernel@vger.kernel.org>,
	"Christoph Hellwig" <hch@lst.de>,
	"Aneesh Kumar K . V" <aneesh.kumar@linux.ibm.com>
Subject: Re: [PATCH v2 02/18] mm/gup: factor out duplicate code from four routines
Date: Mon, 4 Nov 2019 11:51:18 -0500
Message-ID: <20191104165118.GB5134@redhat.com> (raw)
In-Reply-To: <20191103211813.213227-3-jhubbard@nvidia.com>

On Sun, Nov 03, 2019 at 01:17:57PM -0800, John Hubbard wrote:
> There are four locations in gup.c that have a fair amount of code
> duplication. This means that changing one requires making the same
> changes in four places, not to mention reading the same code four
> times, and wondering if there are subtle differences.
> 
> Factor out the common code into static functions, thus reducing the
> overall line count and the code's complexity.
> 
> Also, take the opportunity to slightly improve the efficiency of the
> error cases, by doing a mass subtraction of the refcount, surrounded
> by get_page()/put_page().
> 
> Also, further simplify (slightly), by waiting until the the successful
> end of each routine, to increment *nr.
> 
> Cc: Ira Weiny <ira.weiny@intel.com>
> Cc: Christoph Hellwig <hch@lst.de>
> Cc: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
> Signed-off-by: John Hubbard <jhubbard@nvidia.com>

Good cleanup.

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

> ---
>  mm/gup.c | 104 ++++++++++++++++++++++++-------------------------------
>  1 file changed, 45 insertions(+), 59 deletions(-)
> 
> diff --git a/mm/gup.c b/mm/gup.c
> index 85caf76b3012..199da99e8ffc 100644
> --- a/mm/gup.c
> +++ b/mm/gup.c
> @@ -1969,6 +1969,34 @@ static int __gup_device_huge_pud(pud_t pud, pud_t *pudp, unsigned long addr,
>  }
>  #endif
>  
> +static int __record_subpages(struct page *page, unsigned long addr,
> +			     unsigned long end, struct page **pages, int nr)
> +{
> +	int nr_recorded_pages = 0;
> +
> +	do {
> +		pages[nr] = page;
> +		nr++;
> +		page++;
> +		nr_recorded_pages++;
> +	} while (addr += PAGE_SIZE, addr != end);
> +	return nr_recorded_pages;
> +}
> +
> +static void put_compound_head(struct page *page, int refs)
> +{
> +	/* Do a get_page() first, in case refs == page->_refcount */
> +	get_page(page);
> +	page_ref_sub(page, refs);
> +	put_page(page);
> +}
> +
> +static void __huge_pt_done(struct page *head, int nr_recorded_pages, int *nr)
> +{
> +	*nr += nr_recorded_pages;
> +	SetPageReferenced(head);
> +}
> +
>  #ifdef CONFIG_ARCH_HAS_HUGEPD
>  static unsigned long hugepte_addr_end(unsigned long addr, unsigned long end,
>  				      unsigned long sz)
> @@ -1998,33 +2026,20 @@ static int gup_hugepte(pte_t *ptep, unsigned long sz, unsigned long addr,
>  	/* hugepages are never "special" */
>  	VM_BUG_ON(!pfn_valid(pte_pfn(pte)));
>  
> -	refs = 0;
>  	head = pte_page(pte);
> -
>  	page = head + ((addr & (sz-1)) >> PAGE_SHIFT);
> -	do {
> -		VM_BUG_ON(compound_head(page) != head);
> -		pages[*nr] = page;
> -		(*nr)++;
> -		page++;
> -		refs++;
> -	} while (addr += PAGE_SIZE, addr != end);
> +	refs = __record_subpages(page, addr, end, pages, *nr);
>  
>  	head = try_get_compound_head(head, refs);
> -	if (!head) {
> -		*nr -= refs;
> +	if (!head)
>  		return 0;
> -	}
>  
>  	if (unlikely(pte_val(pte) != pte_val(*ptep))) {
> -		/* Could be optimized better */
> -		*nr -= refs;
> -		while (refs--)
> -			put_page(head);
> +		put_compound_head(head, refs);
>  		return 0;
>  	}
>  
> -	SetPageReferenced(head);
> +	__huge_pt_done(head, refs, nr);
>  	return 1;
>  }
>  
> @@ -2071,29 +2086,19 @@ static int gup_huge_pmd(pmd_t orig, pmd_t *pmdp, unsigned long addr,
>  					     pages, nr);
>  	}
>  
> -	refs = 0;
>  	page = pmd_page(orig) + ((addr & ~PMD_MASK) >> PAGE_SHIFT);
> -	do {
> -		pages[*nr] = page;
> -		(*nr)++;
> -		page++;
> -		refs++;
> -	} while (addr += PAGE_SIZE, addr != end);
> +	refs = __record_subpages(page, addr, end, pages, *nr);
>  
>  	head = try_get_compound_head(pmd_page(orig), refs);
> -	if (!head) {
> -		*nr -= refs;
> +	if (!head)
>  		return 0;
> -	}
>  
>  	if (unlikely(pmd_val(orig) != pmd_val(*pmdp))) {
> -		*nr -= refs;
> -		while (refs--)
> -			put_page(head);
> +		put_compound_head(head, refs);
>  		return 0;
>  	}
>  
> -	SetPageReferenced(head);
> +	__huge_pt_done(head, refs, nr);
>  	return 1;
>  }
>  
> @@ -2114,29 +2119,19 @@ static int gup_huge_pud(pud_t orig, pud_t *pudp, unsigned long addr,
>  					     pages, nr);
>  	}
>  
> -	refs = 0;
>  	page = pud_page(orig) + ((addr & ~PUD_MASK) >> PAGE_SHIFT);
> -	do {
> -		pages[*nr] = page;
> -		(*nr)++;
> -		page++;
> -		refs++;
> -	} while (addr += PAGE_SIZE, addr != end);
> +	refs = __record_subpages(page, addr, end, pages, *nr);
>  
>  	head = try_get_compound_head(pud_page(orig), refs);
> -	if (!head) {
> -		*nr -= refs;
> +	if (!head)
>  		return 0;
> -	}
>  
>  	if (unlikely(pud_val(orig) != pud_val(*pudp))) {
> -		*nr -= refs;
> -		while (refs--)
> -			put_page(head);
> +		put_compound_head(head, refs);
>  		return 0;
>  	}
>  
> -	SetPageReferenced(head);
> +	__huge_pt_done(head, refs, nr);
>  	return 1;
>  }
>  
> @@ -2151,29 +2146,20 @@ static int gup_huge_pgd(pgd_t orig, pgd_t *pgdp, unsigned long addr,
>  		return 0;
>  
>  	BUILD_BUG_ON(pgd_devmap(orig));
> -	refs = 0;
> +
>  	page = pgd_page(orig) + ((addr & ~PGDIR_MASK) >> PAGE_SHIFT);
> -	do {
> -		pages[*nr] = page;
> -		(*nr)++;
> -		page++;
> -		refs++;
> -	} while (addr += PAGE_SIZE, addr != end);
> +	refs = __record_subpages(page, addr, end, pages, *nr);
>  
>  	head = try_get_compound_head(pgd_page(orig), refs);
> -	if (!head) {
> -		*nr -= refs;
> +	if (!head)
>  		return 0;
> -	}
>  
>  	if (unlikely(pgd_val(orig) != pgd_val(*pgdp))) {
> -		*nr -= refs;
> -		while (refs--)
> -			put_page(head);
> +		put_compound_head(head, refs);
>  		return 0;
>  	}
>  
> -	SetPageReferenced(head);
> +	__huge_pt_done(head, refs, nr);
>  	return 1;
>  }
>  
> -- 
> 2.23.0
> 


  reply index

Thread overview: 57+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-11-03 21:17 [PATCH v2 00/18] mm/gup: track dma-pinned pages: FOLL_PIN, FOLL_LONGTERM John Hubbard
2019-11-03 21:17 ` [PATCH v2 01/18] mm/gup: pass flags arg to __gup_device_* functions John Hubbard
2019-11-04 16:39   ` Jerome Glisse
2019-11-03 21:17 ` [PATCH v2 02/18] mm/gup: factor out duplicate code from four routines John Hubbard
2019-11-04 16:51   ` Jerome Glisse [this message]
2019-11-03 21:17 ` [PATCH v2 03/18] goldish_pipe: rename local pin_user_pages() routine John Hubbard
2019-11-04 16:52   ` Jerome Glisse
2019-11-03 21:17 ` [PATCH v2 04/18] media/v4l2-core: set pages dirty upon releasing DMA buffers John Hubbard
2019-11-10 10:10   ` Hans Verkuil
2019-11-11 21:46     ` John Hubbard
2019-11-03 21:18 ` [PATCH v2 05/18] mm/gup: introduce pin_user_pages*() and FOLL_PIN John Hubbard
2019-11-04 17:33   ` Jerome Glisse
2019-11-04 19:04     ` John Hubbard
2019-11-04 19:18       ` Jerome Glisse
2019-11-04 19:30         ` John Hubbard
2019-11-04 19:52           ` Jerome Glisse
2019-11-04 20:09             ` John Hubbard
2019-11-04 20:31               ` Jason Gunthorpe
2019-11-04 20:40                 ` John Hubbard
2019-11-04 20:31               ` Jerome Glisse
2019-11-04 20:37                 ` Jason Gunthorpe
2019-11-04 20:57                   ` John Hubbard
2019-11-04 21:15                     ` Jason Gunthorpe
2019-11-04 21:34                       ` John Hubbard
2019-11-04 20:33   ` David Rientjes
2019-11-04 20:48     ` Jerome Glisse
2019-11-05 13:10   ` Mike Rapoport
2019-11-05 19:00     ` John Hubbard
2019-11-07  2:25       ` Ira Weiny
2019-11-07  8:07       ` Mike Rapoport
2019-11-03 21:18 ` [PATCH v2 06/18] goldish_pipe: convert to pin_user_pages() and put_user_page() John Hubbard
2019-11-03 21:18 ` [PATCH v2 07/18] infiniband: set FOLL_PIN, FOLL_LONGTERM via pin_longterm_pages*() John Hubbard
2019-11-04 20:33   ` Jason Gunthorpe
2019-11-04 20:48     ` John Hubbard
2019-11-04 20:57       ` Jason Gunthorpe
2019-11-04 22:03         ` John Hubbard
2019-11-05  2:32           ` Jason Gunthorpe
2019-11-07  2:26         ` Ira Weiny
2019-11-03 21:18 ` [PATCH v2 08/18] mm/process_vm_access: set FOLL_PIN via pin_user_pages_remote() John Hubbard
2019-11-04 17:41   ` Jerome Glisse
2019-11-03 21:18 ` [PATCH v2 09/18] drm/via: set FOLL_PIN via pin_user_pages_fast() John Hubbard
2019-11-04 17:44   ` Jerome Glisse
2019-11-04 18:22     ` John Hubbard
2019-11-03 21:18 ` [PATCH v2 10/18] fs/io_uring: set FOLL_PIN via pin_user_pages() John Hubbard
2019-11-03 21:18 ` [PATCH v2 11/18] net/xdp: " John Hubbard
2019-11-03 21:18 ` [PATCH v2 12/18] mm/gup: track FOLL_PIN pages John Hubbard
2019-11-04 18:52   ` Jerome Glisse
2019-11-04 22:49     ` John Hubbard
2019-11-04 23:49       ` Jerome Glisse
2019-11-05  0:18         ` John Hubbard
2019-11-03 21:18 ` [PATCH v2 13/18] media/v4l2-core: pin_longterm_pages (FOLL_PIN) and put_user_page() conversion John Hubbard
2019-11-10 10:11   ` Hans Verkuil
2019-11-03 21:18 ` [PATCH v2 14/18] vfio, mm: " John Hubbard
2019-11-03 21:18 ` [PATCH v2 15/18] powerpc: book3s64: convert to pin_longterm_pages() and put_user_page() John Hubbard
2019-11-03 21:18 ` [PATCH v2 16/18] mm/gup_benchmark: support pin_user_pages() and related calls John Hubbard
2019-11-03 21:18 ` [PATCH v2 17/18] selftests/vm: run_vmtests: invoke gup_benchmark with basic FOLL_PIN coverage John Hubbard
2019-11-03 21:18 ` [PATCH v2 18/18] mm/gup: remove support for gup(FOLL_LONGTERM) John Hubbard

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