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Subject: Re: [PATCH v3] mm/slab: Improve performance of gathering slabinfo
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To: Eric Dumazet <eric.dumazet@gmail.com>
References: <1471458050-29622-1-git-send-email-aruna.ramakrishna@oracle.com>
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Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org,
        Mike Kravetz <mike.kravetz@oracle.com>,
        Christoph Lameter <cl@linux.com>, Pekka Enberg <penberg@kernel.org>,
        David Rientjes <rientjes@google.com>,
        Joonsoo Kim <iamjoonsoo.kim@lge.com>,
        Andrew Morton <akpm@linux-foundation.org>
From: Aruna Ramakrishna <aruna.ramakrishna@oracle.com>
Message-ID: <a747d233-5e27-20c3-7e06-cee8d9f2bda1@oracle.com>
Date: Wed, 17 Aug 2016 12:25:33 -0700
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On 08/17/2016 12:03 PM, Eric Dumazet wrote:
> On Wed, 2016-08-17 at 11:20 -0700, Aruna Ramakrishna wrote:
> ]
>> -		list_for_each_entry(page, &n->slabs_full, lru) {
>> -			if (page->active != cachep->num && !error)
>> -				error = "slabs_full accounting error";
>> -			active_objs += cachep->num;
>> -			active_slabs++;
>> -		}
>
> Since you only removed this loop, you could track only number of
> full_slabs.
>
> This would avoid messing with n->num_slabs all over the places in fast
> path.
>
> Please also update slab_out_of_memory()
>

Eric,

Right now, n->num_slabs is modified only when a slab is detached from 
slabs_free (i.e. in drain_freelist and free_block) or when a new one is 
attached in cache_grow_end. None of those 3 calls are in the fast path, 
right? Tracking just full_slabs would also involve similar changes: 
decrement when a slab moves from full to partial during free_block, and 
increment when it moves from partial/free to full after allocation in 
fixup_slab_list. So I don't see what the real difference/advantage is.

I will update slab_out_of_memory and remove the slabs_full list 
traversal there too.

Thanks,
Aruna