[v4,02/23] mm/gup: factor out duplicate code from four routines
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Message ID 20191113042710.3997854-3-jhubbard@nvidia.com
State New
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Series
  • mm/gup: track dma-pinned pages: FOLL_PIN, FOLL_LONGTERM
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Commit Message

John Hubbard Nov. 13, 2019, 4:26 a.m. UTC
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.

Reviewed-by: Jérôme Glisse <jglisse@redhat.com>
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>
---
 mm/gup.c | 104 ++++++++++++++++++++++++-------------------------------
 1 file changed, 45 insertions(+), 59 deletions(-)

Comments

Jan Kara Nov. 13, 2019, 11:15 a.m. UTC | #1
On Tue 12-11-19 20:26:49, 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.
> 
> Reviewed-by: Jérôme Glisse <jglisse@redhat.com>
> 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>

> 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;
> +}

Why don't you pass in already pages + nr?

> +
> +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);
> +}

I don't find this last helper very useful. It seems to muddy water more
than necessary...

Other than that the cleanup looks nice to me.

								Honza
John Hubbard Nov. 13, 2019, 11:12 p.m. UTC | #2
On 11/13/19 3:15 AM, Jan Kara wrote:
> On Tue 12-11-19 20:26:49, 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.
>>
>> Reviewed-by: Jérôme Glisse <jglisse@redhat.com>
>> 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>
> 
>> 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;
>> +}
> 
> Why don't you pass in already pages + nr?

Aha, that does save a function argument. Will do.

...
>> +static void __huge_pt_done(struct page *head, int nr_recorded_pages, int *nr)
>> +{
>> +	*nr += nr_recorded_pages;
>> +	SetPageReferenced(head);
>> +}
> 
> I don't find this last helper very useful. It seems to muddy water more
> than necessary...

Yes, I suspect it's rather unloved, and the fact that it was hard to accurately
name should have been a big hint to not do it. I'll remove the helper and
put the lines back in directly.


thanks,

Patch
diff mbox series

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;
 }