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

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Date:	Fri, 4 Dec 2015 21:43:02 +0800
From:	Geliang Tang <geliangtang@....com>
To:	Christoph Lameter <cl@...ux.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, Geliang Tang <geliangtang@....com>
Subject: Re: [PATCH v2] mm/slab.c: use list_{empty_careful,last_entry} in
 drain_freelist

On Thu, Dec 03, 2015 at 08:53:21AM -0600, Christoph Lameter wrote:
> 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?

Yes. list_empty() is OK.

> 
> >  			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???

The original code delete the page from the tail of slabs_free list.

> 
> 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?

Sorry, I don't really understand what do you mean. Can you please specify
it a little bit?

Thanks.

- Geliang

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

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