2020-08-18 18:48:21

by Yu Zhao

Subject: [PATCH v2 2/3] mm: remove superfluous __ClearPageActive()

To activate a page, mark_page_accessed() always holds a reference
on it. It either gets a new reference when adding a page to
lru_pvecs.activate_page or reuses an existing one it previously
got when it added a page to lru_pvecs.lru_add. So it doesn't call
SetPageActive() on a page that doesn't have any reference left.
Therefore, the race is impossible these days (I didn't brother to
dig into its history).

For other paths, namely reclaim and migration, a reference count is
always held while calling SetPageActive() on a page.

SetPageSlabPfmemalloc() also uses SetPageActive(), but it's irrelevant
to LRU pages.

Signed-off-by: Yu Zhao <[email protected]>
---
mm/memremap.c | 2 --
mm/swap.c | 2 --
2 files changed, 4 deletions(-)

diff --git a/mm/memremap.c b/mm/memremap.c
index 03e38b7a38f1..3a06eb91cb59 100644
--- a/mm/memremap.c
+++ b/mm/memremap.c
@@ -451,8 +451,6 @@ void free_devmap_managed_page(struct page *page)
return;
}

- /* Clear Active bit in case of parallel mark_page_accessed */
- __ClearPageActive(page);
__ClearPageWaiters(page);

mem_cgroup_uncharge(page);
diff --git a/mm/swap.c b/mm/swap.c
index 25c4043491b3..999a84dbe12c 100644
--- a/mm/swap.c
+++ b/mm/swap.c
@@ -900,8 +900,6 @@ void release_pages(struct page **pages, int nr)
del_page_from_lru_list(page, lruvec, page_off_lru(page));
}

- /* Clear Active bit in case of parallel mark_page_accessed */
- __ClearPageActive(page);
__ClearPageWaiters(page);

list_add(&page->lru, &pages_to_free);
--
2.28.0.220.ged08abb693-goog

2020-08-19 23:06:39

by Yang Shi

Subject: Re: [PATCH v2 2/3] mm: remove superfluous __ClearPageActive()

On Tue, Aug 18, 2020 at 11:47 AM Yu Zhao <[email protected]> wrote:
>
> To activate a page, mark_page_accessed() always holds a reference
> on it. It either gets a new reference when adding a page to
> lru_pvecs.activate_page or reuses an existing one it previously
> got when it added a page to lru_pvecs.lru_add. So it doesn't call
> SetPageActive() on a page that doesn't have any reference left.
> Therefore, the race is impossible these days (I didn't brother to
> dig into its history).
>
> For other paths, namely reclaim and migration, a reference count is
> always held while calling SetPageActive() on a page.
>
> SetPageSlabPfmemalloc() also uses SetPageActive(), but it's irrelevant
> to LRU pages.

Seems fine to me. Reviewed-by: Yang Shi <[email protected]>

>
> Signed-off-by: Yu Zhao <[email protected]>
> ---
> mm/memremap.c | 2 --
> mm/swap.c | 2 --
> 2 files changed, 4 deletions(-)
>
> diff --git a/mm/memremap.c b/mm/memremap.c
> index 03e38b7a38f1..3a06eb91cb59 100644
> --- a/mm/memremap.c
> +++ b/mm/memremap.c
> @@ -451,8 +451,6 @@ void free_devmap_managed_page(struct page *page)
> return;
> }
>
> - /* Clear Active bit in case of parallel mark_page_accessed */
> - __ClearPageActive(page);
> __ClearPageWaiters(page);
>
> mem_cgroup_uncharge(page);
> diff --git a/mm/swap.c b/mm/swap.c
> index 25c4043491b3..999a84dbe12c 100644
> --- a/mm/swap.c
> +++ b/mm/swap.c
> @@ -900,8 +900,6 @@ void release_pages(struct page **pages, int nr)
> del_page_from_lru_list(page, lruvec, page_off_lru(page));
> }
>
> - /* Clear Active bit in case of parallel mark_page_accessed */
> - __ClearPageActive(page);
> __ClearPageWaiters(page);
>
> list_add(&page->lru, &pages_to_free);
> --
> 2.28.0.220.ged08abb693-goog
>
>