mm, thp: Do not queue fully unmapped pages for deferred split
diff mbox series

Message ID 20190913091849.11151-1-kirill.shutemov@linux.intel.com
State New
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Series
  • mm, thp: Do not queue fully unmapped pages for deferred split
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Commit Message

Kirill A. Shutemov Sept. 13, 2019, 9:18 a.m. UTC
Adding fully unmapped pages into deferred split queue is not productive:
these pages are about to be freed or they are pinned and cannot be split
anyway.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
---
 mm/rmap.c | 14 ++++++++++----
 1 file changed, 10 insertions(+), 4 deletions(-)

Comments

Michal Hocko Sept. 16, 2019, 10:36 a.m. UTC | #1
On Fri 13-09-19 12:18:49, Kirill A. Shutemov wrote:
> Adding fully unmapped pages into deferred split queue is not productive:
> these pages are about to be freed or they are pinned and cannot be split
> anyway.
> 
> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
> ---
>  mm/rmap.c | 14 ++++++++++----
>  1 file changed, 10 insertions(+), 4 deletions(-)
> 
> diff --git a/mm/rmap.c b/mm/rmap.c
> index 003377e24232..45388f1bf317 100644
> --- a/mm/rmap.c
> +++ b/mm/rmap.c
> @@ -1271,12 +1271,20 @@ static void page_remove_anon_compound_rmap(struct page *page)
>  	if (TestClearPageDoubleMap(page)) {
>  		/*
>  		 * Subpages can be mapped with PTEs too. Check how many of
> -		 * themi are still mapped.
> +		 * them are still mapped.
>  		 */
>  		for (i = 0, nr = 0; i < HPAGE_PMD_NR; i++) {
>  			if (atomic_add_negative(-1, &page[i]._mapcount))
>  				nr++;
>  		}
> +
> +		/*
> +		 * Queue the page for deferred split if at least one small
> +		 * page of the compound page is unmapped, but at least one
> +		 * small page is still mapped.
> +		 */
> +		if (nr && nr < HPAGE_PMD_NR)
> +			deferred_split_huge_page(page);

You've set nr to zero in the for loop so this cannot work AFAICS.

>  	} else {
>  		nr = HPAGE_PMD_NR;
>  	}
> @@ -1284,10 +1292,8 @@ static void page_remove_anon_compound_rmap(struct page *page)
>  	if (unlikely(PageMlocked(page)))
>  		clear_page_mlock(page);
>  
> -	if (nr) {
> +	if (nr)
>  		__mod_node_page_state(page_pgdat(page), NR_ANON_MAPPED, -nr);
> -		deferred_split_huge_page(page);
> -	}
>  }
>  
>  /**
> -- 
> 2.21.0
Vlastimil Babka Sept. 16, 2019, 11:11 a.m. UTC | #2
On 9/16/19 12:36 PM, Michal Hocko wrote:
> On Fri 13-09-19 12:18:49, Kirill A. Shutemov wrote:
>> Adding fully unmapped pages into deferred split queue is not productive:
>> these pages are about to be freed or they are pinned and cannot be split
>> anyway.
>> 
>> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
>> ---
>>  mm/rmap.c | 14 ++++++++++----
>>  1 file changed, 10 insertions(+), 4 deletions(-)
>> 
>> diff --git a/mm/rmap.c b/mm/rmap.c
>> index 003377e24232..45388f1bf317 100644
>> --- a/mm/rmap.c
>> +++ b/mm/rmap.c
>> @@ -1271,12 +1271,20 @@ static void page_remove_anon_compound_rmap(struct page *page)
>>  	if (TestClearPageDoubleMap(page)) {
>>  		/*
>>  		 * Subpages can be mapped with PTEs too. Check how many of
>> -		 * themi are still mapped.
>> +		 * them are still mapped.
>>  		 */
>>  		for (i = 0, nr = 0; i < HPAGE_PMD_NR; i++) {
>>  			if (atomic_add_negative(-1, &page[i]._mapcount))
>>  				nr++;
>>  		}
>> +
>> +		/*
>> +		 * Queue the page for deferred split if at least one small
>> +		 * page of the compound page is unmapped, but at least one
>> +		 * small page is still mapped.
>> +		 */
>> +		if (nr && nr < HPAGE_PMD_NR)
>> +			deferred_split_huge_page(page);
> 
> You've set nr to zero in the for loop so this cannot work AFAICS.

The for loop then does nr++ for each subpage that's still mapped?


>>  	} else {
>>  		nr = HPAGE_PMD_NR;
>>  	}
>> @@ -1284,10 +1292,8 @@ static void page_remove_anon_compound_rmap(struct page *page)
>>  	if (unlikely(PageMlocked(page)))
>>  		clear_page_mlock(page);
>>  
>> -	if (nr) {
>> +	if (nr)
>>  		__mod_node_page_state(page_pgdat(page), NR_ANON_MAPPED, -nr);
>> -		deferred_split_huge_page(page);
>> -	}
>>  }
>>  
>>  /**
>> -- 
>> 2.21.0
>
Michal Hocko Sept. 16, 2019, 11:37 a.m. UTC | #3
On Mon 16-09-19 13:11:37, Vlastimil Babka wrote:
> On 9/16/19 12:36 PM, Michal Hocko wrote:
> > On Fri 13-09-19 12:18:49, Kirill A. Shutemov wrote:
> >> Adding fully unmapped pages into deferred split queue is not productive:
> >> these pages are about to be freed or they are pinned and cannot be split
> >> anyway.
> >> 
> >> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
> >> ---
> >>  mm/rmap.c | 14 ++++++++++----
> >>  1 file changed, 10 insertions(+), 4 deletions(-)
> >> 
> >> diff --git a/mm/rmap.c b/mm/rmap.c
> >> index 003377e24232..45388f1bf317 100644
> >> --- a/mm/rmap.c
> >> +++ b/mm/rmap.c
> >> @@ -1271,12 +1271,20 @@ static void page_remove_anon_compound_rmap(struct page *page)
> >>  	if (TestClearPageDoubleMap(page)) {
> >>  		/*
> >>  		 * Subpages can be mapped with PTEs too. Check how many of
> >> -		 * themi are still mapped.
> >> +		 * them are still mapped.
> >>  		 */
> >>  		for (i = 0, nr = 0; i < HPAGE_PMD_NR; i++) {
> >>  			if (atomic_add_negative(-1, &page[i]._mapcount))
> >>  				nr++;
> >>  		}
> >> +
> >> +		/*
> >> +		 * Queue the page for deferred split if at least one small
> >> +		 * page of the compound page is unmapped, but at least one
> >> +		 * small page is still mapped.
> >> +		 */
> >> +		if (nr && nr < HPAGE_PMD_NR)
> >> +			deferred_split_huge_page(page);
> > 
> > You've set nr to zero in the for loop so this cannot work AFAICS.
> 
> The for loop then does nr++ for each subpage that's still mapped?

I am blind obviously. Sorry about the noise. Then the patch looks
correct.
Yang Shi Sept. 16, 2019, 5:22 p.m. UTC | #4
On Fri, Sep 13, 2019 at 2:18 AM Kirill A. Shutemov <kirill@shutemov.name> wrote:
>
> Adding fully unmapped pages into deferred split queue is not productive:
> these pages are about to be freed or they are pinned and cannot be split
> anyway.

This change looks good to me. Reviewed-by: Yang Shi <yang.shi@linux.alibaba.com>

>
> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
> ---
>  mm/rmap.c | 14 ++++++++++----
>  1 file changed, 10 insertions(+), 4 deletions(-)
>
> diff --git a/mm/rmap.c b/mm/rmap.c
> index 003377e24232..45388f1bf317 100644
> --- a/mm/rmap.c
> +++ b/mm/rmap.c
> @@ -1271,12 +1271,20 @@ static void page_remove_anon_compound_rmap(struct page *page)
>         if (TestClearPageDoubleMap(page)) {
>                 /*
>                  * Subpages can be mapped with PTEs too. Check how many of
> -                * themi are still mapped.
> +                * them are still mapped.
>                  */
>                 for (i = 0, nr = 0; i < HPAGE_PMD_NR; i++) {
>                         if (atomic_add_negative(-1, &page[i]._mapcount))
>                                 nr++;
>                 }
> +
> +               /*
> +                * Queue the page for deferred split if at least one small
> +                * page of the compound page is unmapped, but at least one
> +                * small page is still mapped.
> +                */
> +               if (nr && nr < HPAGE_PMD_NR)
> +                       deferred_split_huge_page(page);
>         } else {
>                 nr = HPAGE_PMD_NR;
>         }
> @@ -1284,10 +1292,8 @@ static void page_remove_anon_compound_rmap(struct page *page)
>         if (unlikely(PageMlocked(page)))
>                 clear_page_mlock(page);
>
> -       if (nr) {
> +       if (nr)
>                 __mod_node_page_state(page_pgdat(page), NR_ANON_MAPPED, -nr);
> -               deferred_split_huge_page(page);
> -       }
>  }
>
>  /**
> --
> 2.21.0
>
>

Patch
diff mbox series

diff --git a/mm/rmap.c b/mm/rmap.c
index 003377e24232..45388f1bf317 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -1271,12 +1271,20 @@  static void page_remove_anon_compound_rmap(struct page *page)
 	if (TestClearPageDoubleMap(page)) {
 		/*
 		 * Subpages can be mapped with PTEs too. Check how many of
-		 * themi are still mapped.
+		 * them are still mapped.
 		 */
 		for (i = 0, nr = 0; i < HPAGE_PMD_NR; i++) {
 			if (atomic_add_negative(-1, &page[i]._mapcount))
 				nr++;
 		}
+
+		/*
+		 * Queue the page for deferred split if at least one small
+		 * page of the compound page is unmapped, but at least one
+		 * small page is still mapped.
+		 */
+		if (nr && nr < HPAGE_PMD_NR)
+			deferred_split_huge_page(page);
 	} else {
 		nr = HPAGE_PMD_NR;
 	}
@@ -1284,10 +1292,8 @@  static void page_remove_anon_compound_rmap(struct page *page)
 	if (unlikely(PageMlocked(page)))
 		clear_page_mlock(page);
 
-	if (nr) {
+	if (nr)
 		__mod_node_page_state(page_pgdat(page), NR_ANON_MAPPED, -nr);
-		deferred_split_huge_page(page);
-	}
 }
 
 /**