linux-kernel - Re: [PATCH v2] mm/slab.c: use list_{empty_careful,last_entry} in drain

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Message-ID: <alpine.DEB.2.20.1512030850390.7483@east.gentwo.org>
Date:	Thu, 3 Dec 2015 08:53:21 -0600 (CST)
From:	Christoph Lameter <cl@...ux.com>
To:	Geliang Tang <geliangtang@....com>
cc:	Pekka Enberg <penberg@...nel.org>,
	David Rientjes <rientjes@...gle.com>,
	Joonsoo Kim <iamjoonsoo.kim@....com>,
	Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] mm/slab.c: use list_{empty_careful,last_entry} in
 drain_freelist

On Thu, 3 Dec 2015, Geliang Tang wrote:

>  	while (nr_freed < tofree && !list_empty(&n->slabs_free)) {
>
>  		spin_lock_irq(&n->list_lock);
> -		p = n->slabs_free.prev;
> -		if (p == &n->slabs_free) {
> +		if (list_empty_careful(&n->slabs_free)) {

We have taken the lock. Why do we need to be "careful"? list_empty()
shoudl work right?

>  			spin_unlock_irq(&n->list_lock);
>  			goto out;
>  		}
>
> -		page = list_entry(p, struct page, lru);
> +		page = list_last_entry(&n->slabs_free, struct page, lru);

last???

Would the the other new function that returns NULL on the empty list or
the pointer not be useful here too and save some code?

This patch seems to make it difficult to understand the code.
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