diff mbox series

[08/13] mm/migrate: __unmap_and_move() push good newpage to LRU

Message ID 33fb71cf-ea55-123a-bf9d-fdad297cae1@google.com (mailing list archive)
State New
Headers show
Series mm/munlock: rework of mlock+munlock page handling | expand

Commit Message

Hugh Dickins Feb. 6, 2022, 9:43 p.m. UTC
Compaction, NUMA page movement, THP collapse/split, and memory failure
do isolate unevictable pages from their "LRU", losing the record of
mlock_count in doing so (isolators are likely to use page->lru for their
own private lists, so mlock_count has to be presumed lost).

That's unfortunate, and we should put in some work to correct that: one
can imagine a function to build up the mlock_count again - but it would
require i_mmap_rwsem for read, so be careful where it's called.  Or
page_referenced_one() and try_to_unmap_one() might do that extra work.

But one place that can very easily be improved is page migration's
__unmap_and_move(): a small adjustment to where the successful new page
is put back on LRU, and its mlock_count (if any) is built back up by
remove_migration_ptes().

Signed-off-by: Hugh Dickins <hughd@google.com>
---
 mm/migrate.c | 31 +++++++++++++++++++------------
 1 file changed, 19 insertions(+), 12 deletions(-)

Comments

Vlastimil Babka Feb. 11, 2022, 5:19 p.m. UTC | #1
On 2/6/22 22:43, Hugh Dickins wrote:
> Compaction, NUMA page movement, THP collapse/split, and memory failure
> do isolate unevictable pages from their "LRU", losing the record of
> mlock_count in doing so (isolators are likely to use page->lru for their
> own private lists, so mlock_count has to be presumed lost).
> 
> That's unfortunate, and we should put in some work to correct that: one
> can imagine a function to build up the mlock_count again - but it would
> require i_mmap_rwsem for read, so be careful where it's called.  Or
> page_referenced_one() and try_to_unmap_one() might do that extra work.
> 
> But one place that can very easily be improved is page migration's
> __unmap_and_move(): a small adjustment to where the successful new page
> is put back on LRU, and its mlock_count (if any) is built back up by
> remove_migration_ptes().
> 
> Signed-off-by: Hugh Dickins <hughd@google.com>

Acked-by: Vlastimil Babka <vbabka@suse.cz>

> ---
>  mm/migrate.c | 31 +++++++++++++++++++------------
>  1 file changed, 19 insertions(+), 12 deletions(-)
> 
> diff --git a/mm/migrate.c b/mm/migrate.c
> index 7c4223ce2500..f4bcf1541b62 100644
> --- a/mm/migrate.c
> +++ b/mm/migrate.c
> @@ -1032,6 +1032,21 @@ static int __unmap_and_move(struct page *page, struct page *newpage,
>  	if (!page_mapped(page))
>  		rc = move_to_new_page(newpage, page, mode);
>  
> +	/*
> +	 * When successful, push newpage to LRU immediately: so that if it
> +	 * turns out to be an mlocked page, remove_migration_ptes() will
> +	 * automatically build up the correct newpage->mlock_count for it.
> +	 *
> +	 * We would like to do something similar for the old page, when
> +	 * unsuccessful, and other cases when a page has been temporarily
> +	 * isolated from the unevictable LRU: but this case is the easiest.
> +	 */
> +	if (rc == MIGRATEPAGE_SUCCESS) {
> +		lru_cache_add(newpage);
> +		if (page_was_mapped)
> +			lru_add_drain();
> +	}
> +
>  	if (page_was_mapped)
>  		remove_migration_ptes(page,
>  			rc == MIGRATEPAGE_SUCCESS ? newpage : page, false);
> @@ -1045,20 +1060,12 @@ static int __unmap_and_move(struct page *page, struct page *newpage,
>  	unlock_page(page);
>  out:
>  	/*
> -	 * If migration is successful, decrease refcount of the newpage
> +	 * If migration is successful, decrease refcount of the newpage,
>  	 * which will not free the page because new page owner increased
> -	 * refcounter. As well, if it is LRU page, add the page to LRU
> -	 * list in here. Use the old state of the isolated source page to
> -	 * determine if we migrated a LRU page. newpage was already unlocked
> -	 * and possibly modified by its owner - don't rely on the page
> -	 * state.
> +	 * refcounter.
>  	 */
> -	if (rc == MIGRATEPAGE_SUCCESS) {
> -		if (unlikely(!is_lru))
> -			put_page(newpage);
> -		else
> -			putback_lru_page(newpage);
> -	}
> +	if (rc == MIGRATEPAGE_SUCCESS)
> +		put_page(newpage);
>  
>  	return rc;
>  }
diff mbox series

Patch

diff --git a/mm/migrate.c b/mm/migrate.c
index 7c4223ce2500..f4bcf1541b62 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -1032,6 +1032,21 @@  static int __unmap_and_move(struct page *page, struct page *newpage,
 	if (!page_mapped(page))
 		rc = move_to_new_page(newpage, page, mode);
 
+	/*
+	 * When successful, push newpage to LRU immediately: so that if it
+	 * turns out to be an mlocked page, remove_migration_ptes() will
+	 * automatically build up the correct newpage->mlock_count for it.
+	 *
+	 * We would like to do something similar for the old page, when
+	 * unsuccessful, and other cases when a page has been temporarily
+	 * isolated from the unevictable LRU: but this case is the easiest.
+	 */
+	if (rc == MIGRATEPAGE_SUCCESS) {
+		lru_cache_add(newpage);
+		if (page_was_mapped)
+			lru_add_drain();
+	}
+
 	if (page_was_mapped)
 		remove_migration_ptes(page,
 			rc == MIGRATEPAGE_SUCCESS ? newpage : page, false);
@@ -1045,20 +1060,12 @@  static int __unmap_and_move(struct page *page, struct page *newpage,
 	unlock_page(page);
 out:
 	/*
-	 * If migration is successful, decrease refcount of the newpage
+	 * If migration is successful, decrease refcount of the newpage,
 	 * which will not free the page because new page owner increased
-	 * refcounter. As well, if it is LRU page, add the page to LRU
-	 * list in here. Use the old state of the isolated source page to
-	 * determine if we migrated a LRU page. newpage was already unlocked
-	 * and possibly modified by its owner - don't rely on the page
-	 * state.
+	 * refcounter.
 	 */
-	if (rc == MIGRATEPAGE_SUCCESS) {
-		if (unlikely(!is_lru))
-			put_page(newpage);
-		else
-			putback_lru_page(newpage);
-	}
+	if (rc == MIGRATEPAGE_SUCCESS)
+		put_page(newpage);
 
 	return rc;
 }