linux-kernel - Re: [RFC PATCH 68/86] treewide: mm: remove cond

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Date:   Wed, 8 Nov 2023 08:49:18 +0100
From:   Vlastimil Babka <vbabka@...e.cz>
To:     Sergey Senozhatsky <senozhatsky@...omium.org>,
        Ankur Arora <ankur.a.arora@...cle.com>
Cc:     linux-kernel@...r.kernel.org, tglx@...utronix.de,
        peterz@...radead.org, torvalds@...ux-foundation.org,
        paulmck@...nel.org, linux-mm@...ck.org, x86@...nel.org,
        akpm@...ux-foundation.org, luto@...nel.org, bp@...en8.de,
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        Seth Jennings <sjenning@...hat.com>,
        Dan Streetman <ddstreet@...e.org>
Subject: Re: [RFC PATCH 68/86] treewide: mm: remove cond_resched()

On 11/8/23 02:28, Sergey Senozhatsky wrote:
> On (23/11/07 15:08), Ankur Arora wrote:
> [..]
>> +++ b/mm/zsmalloc.c
>> @@ -2029,7 +2029,6 @@ static unsigned long __zs_compact(struct zs_pool *pool,
>>  			dst_zspage = NULL;
>>  
>>  			spin_unlock(&pool->lock);
>> -			cond_resched();
>>  			spin_lock(&pool->lock);
>>  		}
>>  	}
> 
> I'd personally prefer to have a comment explaining why we do that
> spin_unlock/spin_lock sequence, which may look confusing to people.

Wonder if it would make sense to have a lock operation that does the
unlock/lock as a self-documenting thing, and maybe could also be optimized
to first check if there's a actually a need for it (because TIF_NEED_RESCHED
or lock is contended).

> Maybe would make sense to put a nice comment in all similar cases.
> For instance:
> 
>   	rcu_read_unlock();
>  -	cond_resched();
>   	rcu_read_lock();