2024-02-28 06:04:42

by Sergey Senozhatsky

Subject: Re: [PATCH 1/2] mm/zsmalloc: don't hold locks of all pages when free_zspage()

On (24/02/27 03:02), Chengming Zhou wrote:
> static void __free_zspage(struct zs_pool *pool, struct size_class *class,
> struct zspage *zspage)
> {
> @@ -834,13 +841,12 @@ static void __free_zspage(struct zs_pool *pool, struct size_class *class,
> VM_BUG_ON_PAGE(!PageLocked(page), page);

Who owns page lock here if free_zspage() doesn't trylock_zspage() no longer?

> next = get_next_page(page);
> reset_page(page);
> - unlock_page(page);
> dec_zone_page_state(page, NR_ZSPAGES);
> put_page(page);
> page = next;
> } while (page != NULL);
>
> - cache_free_zspage(pool, zspage);
> + call_rcu(&zspage->rcu_head, rcu_free_zspage);
>
> class_stat_dec(class, ZS_OBJS_ALLOCATED, class->objs_per_zspage);
> atomic_long_sub(class->pages_per_zspage, &pool->pages_allocated);
> @@ -852,16 +858,6 @@ static void free_zspage(struct zs_pool *pool, struct size_class *class,
> VM_BUG_ON(get_zspage_inuse(zspage));
> VM_BUG_ON(list_empty(&zspage->list));
>
> - /*
> - * Since zs_free couldn't be sleepable, this function cannot call
> - * lock_page. The page locks trylock_zspage got will be released
> - * by __free_zspage.
> - */
> - if (!trylock_zspage(zspage)) {
> - kick_deferred_free(pool);
> - return;
> - }
> -
> remove_zspage(class, zspage);
> __free_zspage(pool, class, zspage);
> }

2024-02-28 06:44:31

by Chengming Zhou

Subject: Re: [PATCH 1/2] mm/zsmalloc: don't hold locks of all pages when free_zspage()

On 2024/2/28 14:01, Sergey Senozhatsky wrote:
> On (24/02/27 03:02), Chengming Zhou wrote:
>> static void __free_zspage(struct zs_pool *pool, struct size_class *class,
>> struct zspage *zspage)
>> {
>> @@ -834,13 +841,12 @@ static void __free_zspage(struct zs_pool *pool, struct size_class *class,
>> VM_BUG_ON_PAGE(!PageLocked(page), page);
>
> Who owns page lock here if free_zspage() doesn't trylock_zspage() no longer?

Right, it should be removed.

>
>> next = get_next_page(page);
>> reset_page(page);
>> - unlock_page(page);
>> dec_zone_page_state(page, NR_ZSPAGES);
>> put_page(page);
>> page = next;
>> } while (page != NULL);
>>
>> - cache_free_zspage(pool, zspage);
>> + call_rcu(&zspage->rcu_head, rcu_free_zspage);
>>
>> class_stat_dec(class, ZS_OBJS_ALLOCATED, class->objs_per_zspage);
>> atomic_long_sub(class->pages_per_zspage, &pool->pages_allocated);
>> @@ -852,16 +858,6 @@ static void free_zspage(struct zs_pool *pool, struct size_class *class,
>> VM_BUG_ON(get_zspage_inuse(zspage));
>> VM_BUG_ON(list_empty(&zspage->list));
>>
>> - /*
>> - * Since zs_free couldn't be sleepable, this function cannot call
>> - * lock_page. The page locks trylock_zspage got will be released
>> - * by __free_zspage.
>> - */
>> - if (!trylock_zspage(zspage)) {
>> - kick_deferred_free(pool);
>> - return;
>> - }
>> -
>> remove_zspage(class, zspage);
>> __free_zspage(pool, class, zspage);
>> }