Re: [RFC 2/6] mm, mempolicy: stop adjusting current->il_next in mpol_rebind_nodemask()

From: Vlastimil Babka <vbabka@suse.cz>
To: Christoph Lameter <cl@linux.com>
Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org,
	cgroups@vger.kernel.org, Li Zefan <lizefan@huawei.com>,
	Michal Hocko <mhocko@kernel.org>,
	Mel Gorman <mgorman@techsingularity.net>,
	David Rientjes <rientjes@google.com>,
	Hugh Dickins <hughd@google.com>,
	Andrea Arcangeli <aarcange@redhat.com>,
	Anshuman Khandual <khandual@linux.vnet.ibm.com>,
	"Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Subject: Re: [RFC 2/6] mm, mempolicy: stop adjusting current->il_next in mpol_rebind_nodemask()
Date: Wed, 12 Apr 2017 23:18:53 +0200	[thread overview]
Message-ID: <a750d0cb-9583-01bf-1bc4-870e785c7e07@suse.cz> (raw)
In-Reply-To: <alpine.DEB.2.20.1704121607520.28335@east.gentwo.org>

On 12.4.2017 23:16, Christoph Lameter wrote:
> On Wed, 12 Apr 2017, Vlastimil Babka wrote:
> 
>>>> Well, interleave_nodes() will then potentially return a node outside of
>>>> the allowed memory policy when its called for the first time after
>>>> mpol_rebind_.. . But thenn it will find the next node within the
>>>> nodemask and work correctly for the next invocations.
>>>
>>> Hmm, you're right. But that could be easily fixed if il_next became il_prev, so
>>> we would return the result of next_node_in(il_prev) and also store it as the new
>>> il_prev, right? I somehow assumed it already worked that way.
> 
> Yup that makes sense and I thought about that when I saw the problem too.
> 
>> @@ -863,6 +856,18 @@ static int lookup_node(unsigned long addr)
>>  	return err;
>>  }
>>
>> +/* Do dynamic interleaving for a process */
>> +static unsigned interleave_nodes(struct mempolicy *policy, bool update_prev)
> 
> Why do you need an additional flag? Would it not be better to always
> update and switch the update_prev=false case to simply use
> next_node_in()?

Looked to me as better wrapping, but probably overengineered, ok. Will change
for v2.