2022-04-29 14:30:17

by Miaohe Lin

Subject: [PATCH 4/9] mm/z3fold: throw warning on failure of trylock_page in z3fold_alloc

If trylock_page fails, the page won't be non-lru movable page. When this
page is freed via free_z3fold_page, it will trigger bug on PageMovable
check in __ClearPageMovable. Throw warning on failure of trylock_page to
guard against such rare case just as what zsmalloc does.

Signed-off-by: Miaohe Lin <[email protected]>
---
mm/z3fold.c | 7 +++----
1 file changed, 3 insertions(+), 4 deletions(-)

diff --git a/mm/z3fold.c b/mm/z3fold.c
index 4e6814c5694f..b3b4e65c107f 100644
--- a/mm/z3fold.c
+++ b/mm/z3fold.c
@@ -1122,10 +1122,9 @@ static int z3fold_alloc(struct z3fold_pool *pool, size_t size, gfp_t gfp,
__SetPageMovable(page, pool->inode->i_mapping);
unlock_page(page);
} else {
- if (trylock_page(page)) {
- __SetPageMovable(page, pool->inode->i_mapping);
- unlock_page(page);
- }
+ WARN_ON(!trylock_page(page));
+ __SetPageMovable(page, pool->inode->i_mapping);
+ unlock_page(page);
}
z3fold_page_lock(zhdr);

--
2.23.0

2022-05-19 07:32:42

by Vitaly Wool

Subject: Re: [PATCH 4/9] mm/z3fold: throw warning on failure of trylock_page in z3fold_alloc

On Fri, Apr 29, 2022 at 8:40 AM Miaohe Lin <[email protected]> wrote:
>
> If trylock_page fails, the page won't be non-lru movable page. When this
> page is freed via free_z3fold_page, it will trigger bug on PageMovable
> check in __ClearPageMovable. Throw warning on failure of trylock_page to
> guard against such rare case just as what zsmalloc does.

I don't see how this is better than what we currently have. We can
check if a page is movable before calling __ClearPageMovable instead.

~Vitaly

> Signed-off-by: Miaohe Lin <[email protected]>
> ---
> mm/z3fold.c | 7 +++----
> 1 file changed, 3 insertions(+), 4 deletions(-)
>
> diff --git a/mm/z3fold.c b/mm/z3fold.c
> index 4e6814c5694f..b3b4e65c107f 100644
> --- a/mm/z3fold.c
> +++ b/mm/z3fold.c
> @@ -1122,10 +1122,9 @@ static int z3fold_alloc(struct z3fold_pool *pool, size_t size, gfp_t gfp,
> __SetPageMovable(page, pool->inode->i_mapping);
> unlock_page(page);
> } else {
> - if (trylock_page(page)) {
> - __SetPageMovable(page, pool->inode->i_mapping);
> - unlock_page(page);
> - }
> + WARN_ON(!trylock_page(page));
> + __SetPageMovable(page, pool->inode->i_mapping);
> + unlock_page(page);
> }
> z3fold_page_lock(zhdr);
>
> --
> 2.23.0
>

2022-05-19 13:44:08

by Miaohe Lin

Subject: Re: [PATCH 4/9] mm/z3fold: throw warning on failure of trylock_page in z3fold_alloc

On 2022/5/19 15:10, Vitaly Wool wrote:
> On Fri, Apr 29, 2022 at 8:40 AM Miaohe Lin <[email protected]> wrote:
>>
>> If trylock_page fails, the page won't be non-lru movable page. When this
>> page is freed via free_z3fold_page, it will trigger bug on PageMovable
>> check in __ClearPageMovable. Throw warning on failure of trylock_page to
>> guard against such rare case just as what zsmalloc does.
>
> I don't see how this is better than what we currently have. We can
> check if a page is movable before calling __ClearPageMovable instead.

Currently the z3fold page (unless headless page) is assumed to be non-lru movable.
We will always do __ClearPageMovable in free_z3fold_page which will trigger BUG_ON
!PageMovable now. And do you mean we should do something like below ?

diff --git a/mm/z3fold.c b/mm/z3fold.c
index f41f8b0d9e9a..a244bb5dcb34 100644
--- a/mm/z3fold.c
+++ b/mm/z3fold.c
@@ -417,9 +417,10 @@ static struct z3fold_header *init_z3fold_page(struct page *page, bool headless,
/* Resets the struct page fields and frees the page */
static void free_z3fold_page(struct page *page, bool headless)
{
- if (!headless) {
+ if (likely(__PageMovable(page))) {
lock_page(page);
- __ClearPageMovable(page);
+ if (PageMovable(page))
+ __ClearPageMovable(page);
unlock_page(page);
}
__free_page(page);

Thanks!

>
> ~Vitaly
>
>> Signed-off-by: Miaohe Lin <[email protected]>
>> ---
>> mm/z3fold.c | 7 +++----
>> 1 file changed, 3 insertions(+), 4 deletions(-)
>>
>> diff --git a/mm/z3fold.c b/mm/z3fold.c
>> index 4e6814c5694f..b3b4e65c107f 100644
>> --- a/mm/z3fold.c
>> +++ b/mm/z3fold.c
>> @@ -1122,10 +1122,9 @@ static int z3fold_alloc(struct z3fold_pool *pool, size_t size, gfp_t gfp,
>> __SetPageMovable(page, pool->inode->i_mapping);
>> unlock_page(page);
>> } else {
>> - if (trylock_page(page)) {
>> - __SetPageMovable(page, pool->inode->i_mapping);
>> - unlock_page(page);
>> - }
>> + WARN_ON(!trylock_page(page));
>> + __SetPageMovable(page, pool->inode->i_mapping);
>> + unlock_page(page);
>> }
>> z3fold_page_lock(zhdr);
>>
>> --
>> 2.23.0
>>
> .
>