linux-kernel - Re: [PATCH 1/2] mm/zsmalloc: don't hold locks of all pages when free

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Date: Wed, 28 Feb 2024 14:44:13 +0800
From: Chengming Zhou <chengming.zhou@...ux.dev>
To: Sergey Senozhatsky <senozhatsky@...omium.org>
Cc: yosryahmed@...gle.com, hannes@...xchg.org, nphamcs@...il.com,
 Andrew Morton <akpm@...ux-foundation.org>, Minchan Kim <minchan@...nel.org>,
 linux-kernel@...r.kernel.org, linux-mm@...ck.org
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);
>>  }