linux-kernel - Re: [RFC V2 05/12] cpuset: Add cpuset_inc() inside cpuset

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Message-ID: <8f442e1d-6c4d-990b-74e7-6d9a16c4576f@suse.cz>
Date:   Tue, 31 Jan 2017 15:36:43 +0100
From:   Vlastimil Babka <vbabka@...e.cz>
To:     Mel Gorman <mgorman@...e.de>,
        Anshuman Khandual <khandual@...ux.vnet.ibm.com>
Cc:     linux-kernel@...r.kernel.org, linux-mm@...ck.org, mhocko@...e.com,
        minchan@...nel.org, aneesh.kumar@...ux.vnet.ibm.com,
        bsingharora@...il.com, srikar@...ux.vnet.ibm.com,
        haren@...ux.vnet.ibm.com, jglisse@...hat.com,
        dave.hansen@...el.com, dan.j.williams@...el.com
Subject: Re: [RFC V2 05/12] cpuset: Add cpuset_inc() inside cpuset_init()

On 01/30/2017 09:30 PM, Mel Gorman wrote:
> On Mon, Jan 30, 2017 at 09:05:46AM +0530, Anshuman Khandual wrote:
>> Currently cpusets_enabled() wrongfully returns 0 even if we have a root
>> cpuset configured on the system. This got missed when jump level was
>> introduced in place of number_of_cpusets with the commit 664eeddeef65
>> ("mm: page_alloc: use jump labels to avoid checking number_of_cpusets")
>> . This fixes the problem so that cpusets_enabled() returns positive even
>> for the root cpuset.
>>
>> Fixes: 664eeddeef65 ("mm: page_alloc: use jump labels to avoid")
>> Signed-off-by: Anshuman Khandual <khandual@...ux.vnet.ibm.com>
> 
> Superficially, this appears to always activate the cpuset_enabled
> branch() when it doesn't really make sense that the root cpuset be
> restricted.

Yes that's why root cpuset doesn't "count", as it's not supposed to be
restricted (it's also documented in cpusets.txt) Thus the "Fixes:" tag
is very misleading.

> I strongly suspect it should be altered to cpuset_inc only
> if the root cpuset is configured to isolate memory.
>