linux-kernel - Re: [RFC 2/6] mm, mempolicy: stop adjusting current->il_next in mpol_rebind

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Date:   Wed, 12 Apr 2017 23:18:53 +0200
From:   Vlastimil Babka <vbabka@...e.cz>
To:     Christoph Lameter <cl@...ux.com>
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        cgroups@...r.kernel.org, Li Zefan <lizefan@...wei.com>,
        Michal Hocko <mhocko@...nel.org>,
        Mel Gorman <mgorman@...hsingularity.net>,
        David Rientjes <rientjes@...gle.com>,
        Hugh Dickins <hughd@...gle.com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Anshuman Khandual <khandual@...ux.vnet.ibm.com>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
Subject: Re: [RFC 2/6] mm, mempolicy: stop adjusting current->il_next in
 mpol_rebind_nodemask()

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.