2022-04-29 15:52:26

by Miaohe Lin

Subject: [PATCH 3/9] mm/z3fold: remove buggy use of stale list for allocation

Currently if z3fold couldn't find an unbuddied page it would first try to
pull a page off the stale list. But this approach is problematic. If init
z3fold page fails later, the page should be freed via free_z3fold_page to
clean up the relevant resource instead of using __free_page directly. And
if page is successfully reused, it will BUG_ON later in __SetPageMovable
because it's already non-lru movable page, i.e. PAGE_MAPPING_MOVABLE is
already set in page->mapping. In order to fix all of these issues, we can
simply remove the buggy use of stale list for allocation because can_sleep
should always be false and we never really hit the reusing code path now.

Signed-off-by: Miaohe Lin <[email protected]>
---
mm/z3fold.c | 23 +----------------------
1 file changed, 1 insertion(+), 22 deletions(-)

diff --git a/mm/z3fold.c b/mm/z3fold.c
index 5d8c21f2bc59..4e6814c5694f 100644
--- a/mm/z3fold.c
+++ b/mm/z3fold.c
@@ -1102,28 +1102,7 @@ static int z3fold_alloc(struct z3fold_pool *pool, size_t size, gfp_t gfp,
bud = FIRST;
}

- page = NULL;
- if (can_sleep) {
- spin_lock(&pool->stale_lock);
- zhdr = list_first_entry_or_null(&pool->stale,
- struct z3fold_header, buddy);
- /*
- * Before allocating a page, let's see if we can take one from
- * the stale pages list. cancel_work_sync() can sleep so we
- * limit this case to the contexts where we can sleep
- */
- if (zhdr) {
- list_del(&zhdr->buddy);
- spin_unlock(&pool->stale_lock);
- cancel_work_sync(&zhdr->work);
- page = virt_to_page(zhdr);
- } else {
- spin_unlock(&pool->stale_lock);
- }
- }
- if (!page)
- page = alloc_page(gfp);
-
+ page = alloc_page(gfp);
if (!page)
return -ENOMEM;

--
2.23.0

2022-05-19 10:34:55

by Vitaly Wool

Subject: Re: [PATCH 3/9] mm/z3fold: remove buggy use of stale list for allocation

On Fri, Apr 29, 2022 at 8:41 AM Miaohe Lin <[email protected]> wrote:
>
> Currently if z3fold couldn't find an unbuddied page it would first try to
> pull a page off the stale list. But this approach is problematic. If init
> z3fold page fails later, the page should be freed via free_z3fold_page to
> clean up the relevant resource instead of using __free_page directly. And
> if page is successfully reused, it will BUG_ON later in __SetPageMovable
> because it's already non-lru movable page, i.e. PAGE_MAPPING_MOVABLE is
> already set in page->mapping. In order to fix all of these issues, we can
> simply remove the buggy use of stale list for allocation because can_sleep
> should always be false and we never really hit the reusing code path now.
>
> Signed-off-by: Miaohe Lin <[email protected]>
> ---
> mm/z3fold.c | 23 +----------------------
> 1 file changed, 1 insertion(+), 22 deletions(-)
>
> diff --git a/mm/z3fold.c b/mm/z3fold.c
> index 5d8c21f2bc59..4e6814c5694f 100644
> --- a/mm/z3fold.c
> +++ b/mm/z3fold.c
> @@ -1102,28 +1102,7 @@ static int z3fold_alloc(struct z3fold_pool *pool, size_t size, gfp_t gfp,
> bud = FIRST;
> }
>
> - page = NULL;
> - if (can_sleep) {
> - spin_lock(&pool->stale_lock);
> - zhdr = list_first_entry_or_null(&pool->stale,
> - struct z3fold_header, buddy);
> - /*
> - * Before allocating a page, let's see if we can take one from
> - * the stale pages list. cancel_work_sync() can sleep so we
> - * limit this case to the contexts where we can sleep
> - */
> - if (zhdr) {
> - list_del(&zhdr->buddy);
> - spin_unlock(&pool->stale_lock);
> - cancel_work_sync(&zhdr->work);
> - page = virt_to_page(zhdr);
> - } else {
> - spin_unlock(&pool->stale_lock);
> - }
> - }
> - if (!page)
> - page = alloc_page(gfp);
> -
> + page = alloc_page(gfp);
> if (!page)
> return -ENOMEM;

Reviewed-by: Vitaly Wool <[email protected]>
> --
> 2.23.0
>