On Tue 18-08-20 12:47:04, Yu Zhao wrote:
> Presumably __ClearPageWaiters() was added to follow the previously
> removed __ClearPageActive() pattern.
I do not think so. Please have a look at 62906027091f ("mm: add
PageWaiters indicating tasks are waiting for a page bit") and a
discussion when the patch has been proposed. Sorry I do not have a link
handy but I do remember that the handling was quite subtle.
> Only flags that are in PAGE_FLAGS_CHECK_AT_FREE needs to be properly
> cleared because otherwise we think there may be some kind of leak.
> PG_waiters is not one of those flags and leaving the clearing to
> PAGE_FLAGS_CHECK_AT_PREP is more appropriate.
What is the point of this patch in the first place? Page waiters is
quite subtle and I wouldn't touch it without having a very good reason.
> Signed-off-by: Yu Zhao <yuz...@google.com>
> ---
> include/linux/page-flags.h | 2 +-
> mm/filemap.c | 2 ++
> mm/memremap.c | 2 --
> mm/swap.c | 3 ---
> 4 files changed, 3 insertions(+), 6 deletions(-)
>
> diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h
> index 6be1aa559b1e..dba80a2bdfba 100644
> --- a/include/linux/page-flags.h
> +++ b/include/linux/page-flags.h
> @@ -318,7 +318,7 @@ static inline int TestClearPage##uname(struct page *page)
> { return 0; }
> TESTSETFLAG_FALSE(uname) TESTCLEARFLAG_FALSE(uname)
>
> __PAGEFLAG(Locked, locked, PF_NO_TAIL)
> -PAGEFLAG(Waiters, waiters, PF_ONLY_HEAD) __CLEARPAGEFLAG(Waiters, waiters,
> PF_ONLY_HEAD)
> +PAGEFLAG(Waiters, waiters, PF_ONLY_HEAD)
> PAGEFLAG(Error, error, PF_NO_TAIL) TESTCLEARFLAG(Error, error, PF_NO_TAIL)
> PAGEFLAG(Referenced, referenced, PF_HEAD)
> TESTCLEARFLAG(Referenced, referenced, PF_HEAD)
> diff --git a/mm/filemap.c b/mm/filemap.c
> index 1aaea26556cc..75240c7ef73f 100644
> --- a/mm/filemap.c
> +++ b/mm/filemap.c
> @@ -1079,6 +1079,8 @@ static void wake_up_page_bit(struct page *page, int
> bit_nr)
> * other pages on it.
> *
> * That's okay, it's a rare case. The next waker will clear it.
> + * Otherwise the bit will be cleared by PAGE_FLAGS_CHECK_AT_PREP
> + * when the page is being freed.
> */
> }
> spin_unlock_irqrestore(&q->lock, flags);
> diff --git a/mm/memremap.c b/mm/memremap.c
> index 3a06eb91cb59..a9d02ffaf9e3 100644
> --- a/mm/memremap.c
> +++ b/mm/memremap.c
> @@ -451,8 +451,6 @@ void free_devmap_managed_page(struct page *page)
> return;
> }
>
> - __ClearPageWaiters(page);
> -
> mem_cgroup_uncharge(page);
>
> /*
> diff --git a/mm/swap.c b/mm/swap.c
> index 999a84dbe12c..40bf20a75278 100644
> --- a/mm/swap.c
> +++ b/mm/swap.c
> @@ -90,7 +90,6 @@ static void __page_cache_release(struct page *page)
> del_page_from_lru_list(page, lruvec, page_off_lru(page));
> spin_unlock_irqrestore(&pgdat->lru_lock, flags);
> }
> - __ClearPageWaiters(page);
> }
>
> static void __put_single_page(struct page *page)
> @@ -900,8 +899,6 @@ void release_pages(struct page **pages, int nr)
> del_page_from_lru_list(page, lruvec,
> page_off_lru(page));
> }
>
> - __ClearPageWaiters(page);
> -
> list_add(&page->lru, &pages_to_free);
> }
> if (locked_pgdat)
> --
> 2.28.0.220.ged08abb693-goog
>
--
Michal Hocko
SUSE Labs
