linux-kernel - Re: [PATCH] Show slab memory usage on OOM and SysRq-M

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Date:	Tue, 17 Apr 2007 17:12:13 +0200
From:	Eric Dumazet <dada1@...mosbay.com>
To:	"Pekka Enberg" <penberg@...helsinki.fi>
Cc:	"Pavel Emelianov" <xemul@...ru>, "Andrew Morton" <akpm@...l.org>,
	"Linux Kernel Mailing List" <linux-kernel@...r.kernel.org>,
	devel@...nvz.org, "Kirill Korotaev" <dev@...nvz.org>,
	linux-mm@...ck.org
Subject: Re: [PATCH] Show slab memory usage on OOM and SysRq-M

On Tue, 17 Apr 2007 16:22:48 +0300
"Pekka Enberg" <penberg@...helsinki.fi> wrote:

> Hi,
> 
> On 4/17/07, Pavel Emelianov <xemul@...ru> wrote:
> > +static unsigned long get_cache_size(struct kmem_cache *cachep)
> > +{
> > +       unsigned long slabs;
> > +       struct kmem_list3 *l3;
> > +       struct list_head *lh;
> > +       int node;
> > +
> > +       slabs = 0;
> > +
> > +       for_each_online_node (node) {
> > +               l3 = cachep->nodelists[node];
> > +               if (l3 == NULL)
> > +                       continue;
> > +
> > +               spin_lock(&l3->list_lock);
> > +               list_for_each (lh, &l3->slabs_full)
> > +                       slabs++;
> > +               list_for_each (lh, &l3->slabs_partial)
> > +                       slabs++;
> > +               list_for_each (lh, &l3->slabs_free)
> > +                       slabs++;
> > +               spin_unlock(&l3->list_lock);
> > +       }
> > +
> > +       return slabs * ((PAGE_SIZE << cachep->gfporder) +
> > +               (OFF_SLAB(cachep) ? cachep->slabp_cache->buffer_size : 0));
> > +}
> 
> Considering you're doing this at out_of_memory() time, wouldn't it
> make more sense to add a ->nr_pages to struct kmem_cache and do the
> tracking in kmem_getpages/kmem_freepages?
> 

To avoid a deadlock ? yes...

This nr_pages should be in struct kmem_list3, not in struct kmem_cache, or else you defeat NUMA optimizations if touching a field in kmem_cache at kmem_getpages()/kmem_freepages() time.

       for_each_online_node (node) {
               l3 = cachep->nodelists[node];
               if (l3)
                   slabs += l3->nr_pages; /* dont lock l3->list_lock */
       }
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