2019-07-10 21:40:05

by Henry Burns

Subject: [PATCH] mm/z3fold.c: remove z3fold_migration trylock

z3fold_page_migrate() will never succeed because it attempts to acquire a
lock that has already been taken by migrate.c in __unmap_and_move().

__unmap_and_move() migrate.c
trylock_page(oldpage)
move_to_new_page(oldpage_newpage)
a_ops->migrate_page(oldpage, newpage)
z3fold_page_migrate(oldpage, newpage)
trylock_page(oldpage)


Signed-off-by: Henry Burns <[email protected]>
---
mm/z3fold.c | 6 ------
1 file changed, 6 deletions(-)

diff --git a/mm/z3fold.c b/mm/z3fold.c
index 985732c8b025..9fe9330ab8ae 100644
--- a/mm/z3fold.c
+++ b/mm/z3fold.c
@@ -1335,16 +1335,11 @@ static int z3fold_page_migrate(struct address_space *mapping, struct page *newpa
zhdr = page_address(page);
pool = zhdr_to_pool(zhdr);

- if (!trylock_page(page))
- return -EAGAIN;
-
if (!z3fold_page_trylock(zhdr)) {
- unlock_page(page);
return -EAGAIN;
}
if (zhdr->mapped_count != 0) {
z3fold_page_unlock(zhdr);
- unlock_page(page);
return -EBUSY;
}
new_zhdr = page_address(newpage);
@@ -1376,7 +1371,6 @@ static int z3fold_page_migrate(struct address_space *mapping, struct page *newpa
queue_work_on(new_zhdr->cpu, pool->compact_wq, &new_zhdr->work);

page_mapcount_reset(page);
- unlock_page(page);
put_page(page);
return 0;
}
--
2.22.0.410.gd8fdbe21b5-goog

2019-07-10 21:45:03

by Shakeel Butt

Subject: Re: [PATCH] mm/z3fold.c: remove z3fold_migration trylock

On Wed, Jul 10, 2019 at 2:32 PM Henry Burns <[email protected]> wrote:
>
> z3fold_page_migrate() will never succeed because it attempts to acquire a
> lock that has already been taken by migrate.c in __unmap_and_move().
>
> __unmap_and_move() migrate.c
> trylock_page(oldpage)
> move_to_new_page(oldpage_newpage)
> a_ops->migrate_page(oldpage, newpage)
> z3fold_page_migrate(oldpage, newpage)
> trylock_page(oldpage)
>
>
> Signed-off-by: Henry Burns <[email protected]>

Reviewed-by: Shakeel Butt <[email protected]>

Please add the Fixes tag as well.

> ---
> mm/z3fold.c | 6 ------
> 1 file changed, 6 deletions(-)
>
> diff --git a/mm/z3fold.c b/mm/z3fold.c
> index 985732c8b025..9fe9330ab8ae 100644
> --- a/mm/z3fold.c
> +++ b/mm/z3fold.c
> @@ -1335,16 +1335,11 @@ static int z3fold_page_migrate(struct address_space *mapping, struct page *newpa
> zhdr = page_address(page);
> pool = zhdr_to_pool(zhdr);
>
> - if (!trylock_page(page))
> - return -EAGAIN;
> -
> if (!z3fold_page_trylock(zhdr)) {
> - unlock_page(page);
> return -EAGAIN;
> }
> if (zhdr->mapped_count != 0) {
> z3fold_page_unlock(zhdr);
> - unlock_page(page);
> return -EBUSY;
> }
> new_zhdr = page_address(newpage);
> @@ -1376,7 +1371,6 @@ static int z3fold_page_migrate(struct address_space *mapping, struct page *newpa
> queue_work_on(new_zhdr->cpu, pool->compact_wq, &new_zhdr->work);
>
> page_mapcount_reset(page);
> - unlock_page(page);
> put_page(page);
> return 0;
> }
> --
> 2.22.0.410.gd8fdbe21b5-goog
>

2019-07-10 21:53:25

by Henry Burns

Subject: Re: [PATCH] mm/z3fold.c: remove z3fold_migration trylock

> > z3fold_page_migrate() will never succeed because it attempts to acquire a
> > lock that has already been taken by migrate.c in __unmap_and_move().
> >
> > __unmap_and_move() migrate.c
> > trylock_page(oldpage)
> > move_to_new_page(oldpage_newpage)
> > a_ops->migrate_page(oldpage, newpage)
> > z3fold_page_migrate(oldpage, newpage)
> > trylock_page(oldpage)
> >
> >
> > Signed-off-by: Henry Burns <[email protected]>
>
> Reviewed-by: Shakeel Butt <[email protected]>
>
> Please add the Fixes tag as well.
Fixes: 1f862989b04a ("mm/z3fold.c: support page migration")
>
> > ---
> > mm/z3fold.c | 6 ------
> > 1 file changed, 6 deletions(-)
> >
> > diff --git a/mm/z3fold.c b/mm/z3fold.c
> > index 985732c8b025..9fe9330ab8ae 100644
> > --- a/mm/z3fold.c
> > +++ b/mm/z3fold.c
> > @@ -1335,16 +1335,11 @@ static int z3fold_page_migrate(struct address_space *mapping, struct page *newpa
> > zhdr = page_address(page);
> > pool = zhdr_to_pool(zhdr);
> >
> > - if (!trylock_page(page))
> > - return -EAGAIN;
> > -
> > if (!z3fold_page_trylock(zhdr)) {
> > - unlock_page(page);
> > return -EAGAIN;
> > }
> > if (zhdr->mapped_count != 0) {
> > z3fold_page_unlock(zhdr);
> > - unlock_page(page);
> > return -EBUSY;
> > }
> > new_zhdr = page_address(newpage);
> > @@ -1376,7 +1371,6 @@ static int z3fold_page_migrate(struct address_space *mapping, struct page *newpa
> > queue_work_on(new_zhdr->cpu, pool->compact_wq, &new_zhdr->work);
> >
> > page_mapcount_reset(page);
> > - unlock_page(page);
> > put_page(page);
> > return 0;
> > }
> > --
> > 2.22.0.410.gd8fdbe21b5-goog
> >