diff mbox series

[2/4] mm/swap: use SECTORS_PER_PAGE_SHIFT to clean up code

Message ID 20200505115543.1660-3-thunder.leizhen@huawei.com (mailing list archive)
State New, archived
Headers show
Series eliminate SECTOR related magic numbers and duplicated conversions | expand

Commit Message

Leizhen (ThunderTown) May 5, 2020, 11:55 a.m. UTC 
1. Replace "PAGE_SHIFT - 9" with SECTORS_PER_PAGE_SHIFT

Signed-off-by: Zhen Lei <thunder.leizhen@huawei.com>
---
 mm/page_io.c  |  4 ++--
 mm/swapfile.c | 12 ++++++------
 2 files changed, 8 insertions(+), 8 deletions(-)

Comments

Matthew Wilcox May 5, 2020, 5:25 p.m. UTC | #1 
On Tue, May 05, 2020 at 07:55:41PM +0800, Zhen Lei wrote:
> +++ b/mm/swapfile.c
> @@ -177,8 +177,8 @@ static int discard_swap(struct swap_info_struct *si)
>  
>  	/* Do not discard the swap header page! */
>  	se = first_se(si);
> -	start_block = (se->start_block + 1) << (PAGE_SHIFT - 9);
> -	nr_blocks = ((sector_t)se->nr_pages - 1) << (PAGE_SHIFT - 9);
> +	start_block = (se->start_block + 1) << SECTORS_PER_PAGE_SHIFT;
> +	nr_blocks = ((sector_t)se->nr_pages - 1) << SECTORS_PER_PAGE_SHIFT;

Thinking about this some more, wouldn't this look better?

	start_block = page_sectors(se->start_block + 1);
	nr_block = page_sectors(se->nr_pages - 1);
Leizhen (ThunderTown) May 6, 2020, 1:33 a.m. UTC | #2 
On 2020/5/6 1:25, Matthew Wilcox wrote:
> On Tue, May 05, 2020 at 07:55:41PM +0800, Zhen Lei wrote:
>> +++ b/mm/swapfile.c
>> @@ -177,8 +177,8 @@ static int discard_swap(struct swap_info_struct *si)
>>  
>>  	/* Do not discard the swap header page! */
>>  	se = first_se(si);
>> -	start_block = (se->start_block + 1) << (PAGE_SHIFT - 9);
>> -	nr_blocks = ((sector_t)se->nr_pages - 1) << (PAGE_SHIFT - 9);
>> +	start_block = (se->start_block + 1) << SECTORS_PER_PAGE_SHIFT;
>> +	nr_blocks = ((sector_t)se->nr_pages - 1) << SECTORS_PER_PAGE_SHIFT;
> 
> Thinking about this some more, wouldn't this look better?
> 
> 	start_block = page_sectors(se->start_block + 1);
> 	nr_block = page_sectors(se->nr_pages - 1);
> 

OK，That's fine, it's clearer. And in this way, there won't be more than 80 columns.

> 
> .
>
Leizhen (ThunderTown) May 6, 2020, 3:47 a.m. UTC | #3 
On 2020/5/6 9:33, Leizhen (ThunderTown) wrote:
> 
> 
> On 2020/5/6 1:25, Matthew Wilcox wrote:
>> On Tue, May 05, 2020 at 07:55:41PM +0800, Zhen Lei wrote:
>>> +++ b/mm/swapfile.c
>>> @@ -177,8 +177,8 @@ static int discard_swap(struct swap_info_struct *si)
>>>  
>>>  	/* Do not discard the swap header page! */
>>>  	se = first_se(si);
>>> -	start_block = (se->start_block + 1) << (PAGE_SHIFT - 9);
>>> -	nr_blocks = ((sector_t)se->nr_pages - 1) << (PAGE_SHIFT - 9);
>>> +	start_block = (se->start_block + 1) << SECTORS_PER_PAGE_SHIFT;
>>> +	nr_blocks = ((sector_t)se->nr_pages - 1) << SECTORS_PER_PAGE_SHIFT;
>>
>> Thinking about this some more, wouldn't this look better?
>>
>> 	start_block = page_sectors(se->start_block + 1);
>> 	nr_block = page_sectors(se->nr_pages - 1);
>>
> 
> OK，That's fine, it's clearer. And in this way, there won't be more than 80 columns.

Should we rename "page_sectors" to "page_to_sectors"? Because we may need to define
"sectors_to_page" also.

> 
>>
>> .
>>
Leizhen (ThunderTown) May 6, 2020, 9:16 a.m. UTC | #4 
On 2020/5/6 11:47, Leizhen (ThunderTown) wrote:
> 
> 
> On 2020/5/6 9:33, Leizhen (ThunderTown) wrote:
>>
>>
>> On 2020/5/6 1:25, Matthew Wilcox wrote:
>>> On Tue, May 05, 2020 at 07:55:41PM +0800, Zhen Lei wrote:
>>>> +++ b/mm/swapfile.c
>>>> @@ -177,8 +177,8 @@ static int discard_swap(struct swap_info_struct *si)
>>>>  
>>>>  	/* Do not discard the swap header page! */
>>>>  	se = first_se(si);
>>>> -	start_block = (se->start_block + 1) << (PAGE_SHIFT - 9);
>>>> -	nr_blocks = ((sector_t)se->nr_pages - 1) << (PAGE_SHIFT - 9);
>>>> +	start_block = (se->start_block + 1) << SECTORS_PER_PAGE_SHIFT;
>>>> +	nr_blocks = ((sector_t)se->nr_pages - 1) << SECTORS_PER_PAGE_SHIFT;
>>>
>>> Thinking about this some more, wouldn't this look better?
>>>
>>> 	start_block = page_sectors(se->start_block + 1);
>>> 	nr_block = page_sectors(se->nr_pages - 1);
>>>
>>
>> OK，That's fine, it's clearer. And in this way, there won't be more than 80 columns.
> 
> Should we rename "page_sectors" to "page_to_sectors"? Because we may need to define
> "sectors_to_page" also.

Change the "sectors_to_page" to "sectors_to_npage", npage means "number of pages"
or "page number". To distinguish the use case of "pfn_to_page()" etc. The latter
returns the pointer of "struct page".

> 
>>
>>>
>>> .
>>>
diff mbox series

Patch

diff --git a/mm/page_io.c b/mm/page_io.c
index b1d4f4558e6b..51f25238fd9a 100644
--- a/mm/page_io.c
+++ b/mm/page_io.c
@@ -38,7 +38,7 @@  static struct bio *get_swap_bio(gfp_t gfp_flags,
 
 		bio->bi_iter.bi_sector = map_swap_page(page, &bdev);
 		bio_set_dev(bio, bdev);
-		bio->bi_iter.bi_sector <<= PAGE_SHIFT - 9;
+		bio->bi_iter.bi_sector <<= SECTORS_PER_PAGE_SHIFT;
 		bio->bi_end_io = end_io;
 
 		bio_add_page(bio, page, PAGE_SIZE * hpage_nr_pages(page), 0);
@@ -266,7 +266,7 @@  int swap_writepage(struct page *page, struct writeback_control *wbc)
 
 static sector_t swap_page_sector(struct page *page)
 {
-	return (sector_t)__page_file_index(page) << (PAGE_SHIFT - 9);
+	return (sector_t)__page_file_index(page) << SECTORS_PER_PAGE_SHIFT;
 }
 
 static inline void count_swpout_vm_event(struct page *page)
diff --git a/mm/swapfile.c b/mm/swapfile.c
index 5871a2aa86a5..0871023c0166 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -177,8 +177,8 @@  static int discard_swap(struct swap_info_struct *si)
 
 	/* Do not discard the swap header page! */
 	se = first_se(si);
-	start_block = (se->start_block + 1) << (PAGE_SHIFT - 9);
-	nr_blocks = ((sector_t)se->nr_pages - 1) << (PAGE_SHIFT - 9);
+	start_block = (se->start_block + 1) << SECTORS_PER_PAGE_SHIFT;
+	nr_blocks = ((sector_t)se->nr_pages - 1) << SECTORS_PER_PAGE_SHIFT;
 	if (nr_blocks) {
 		err = blkdev_issue_discard(si->bdev, start_block,
 				nr_blocks, GFP_KERNEL, 0);
@@ -188,8 +188,8 @@  static int discard_swap(struct swap_info_struct *si)
 	}
 
 	for (se = next_se(se); se; se = next_se(se)) {
-		start_block = se->start_block << (PAGE_SHIFT - 9);
-		nr_blocks = (sector_t)se->nr_pages << (PAGE_SHIFT - 9);
+		start_block = se->start_block << SECTORS_PER_PAGE_SHIFT;
+		nr_blocks = (sector_t)se->nr_pages << SECTORS_PER_PAGE_SHIFT;
 
 		err = blkdev_issue_discard(si->bdev, start_block,
 				nr_blocks, GFP_KERNEL, 0);
@@ -240,8 +240,8 @@  static void discard_swap_cluster(struct swap_info_struct *si,
 		start_page += nr_blocks;
 		nr_pages -= nr_blocks;
 
-		start_block <<= PAGE_SHIFT - 9;
-		nr_blocks <<= PAGE_SHIFT - 9;
+		start_block <<= SECTORS_PER_PAGE_SHIFT;
+		nr_blocks <<= SECTORS_PER_PAGE_SHIFT;
 		if (blkdev_issue_discard(si->bdev, start_block,
 					nr_blocks, GFP_NOIO, 0))
 			break;