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Message-ID: <06cb753b-f64f-3679-b365-fbf346cbf828@amd.com>
Date:   Tue, 17 Jan 2023 18:39:03 +0530
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Subject: Re: [RFC PATCH V1 1/1] sched/numa: Enhance vma scanning logic
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To:     David Hildenbrand <david@redhat.com>, linux-kernel@vger.kernel.org,
        linux-mm@kvack.org
Cc:     Ingo Molnar <mingo@redhat.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Juri Lelli <juri.lelli@redhat.com>,
        Vincent Guittot <vincent.guittot@linaro.org>,
        Dietmar Eggemann <dietmar.eggemann@arm.com>,
        Steven Rostedt <rostedt@goodmis.org>,
        Ben Segall <bsegall@google.com>, Mel Gorman <mgorman@suse.de>,
        Daniel Bristot de Oliveira <bristot@redhat.com>,
        Valentin Schneider <vschneid@redhat.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Matthew Wilcox <willy@infradead.org>,
        Vlastimil Babka <vbabka@suse.cz>,
        "Liam R . Howlett" <Liam.Howlett@Oracle.com>,
        Peter Xu <peterx@redhat.com>, xu xin <cgel.zte@gmail.com>,
        Yu Zhao <yuzhao@google.com>, Colin Cross <ccross@google.com>,
        Arnd Bergmann <arnd@arndb.de>, Hugh Dickins <hughd@google.com>,
        Bharata B Rao <bharata@amd.com>,
        Disha Talreja <dishaa.talreja@amd.com>
References: <cover.1673610485.git.raghavendra.kt@amd.com>
 <67bf778d592c39d02444825c416c2ed11d2ef4b2.1673610485.git.raghavendra.kt@amd.com>
 <4ac11b6a-284c-c763-f3c6-45a53c272f47@redhat.com>
From:   Raghavendra K T <raghavendra.kt@amd.com>
In-Reply-To: <4ac11b6a-284c-c763-f3c6-45a53c272f47@redhat.com>
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On 1/17/2023 4:44 PM, David Hildenbrand wrote:
> On 16.01.23 03:25, Raghavendra K T wrote:
>>   During the Numa scanning make sure only relevant vmas of the
>> tasks are scanned.
>>
>> Logic:
>> 1) For the first two time allow unconditional scanning of vmas
>> 2) Store recent 4 unique tasks (last 8bits of PIDs) accessed the vma.
>>    False negetives in case of collison should be fine here.
>> 3) If more than 4 pids exist assume task indeed accessed vma to
>>   to avoid false negetives
>>
>> Co-developed-by: Bharata B Rao <bharata@amd.com>
>> (initial patch to store pid information)
>>
>> Suggested-by: Mel Gorman <mgorman@techsingularity.net>
>> Signed-off-by: Bharata B Rao <bharata@amd.com>
>> Signed-off-by: Raghavendra K T <raghavendra.kt@amd.com>
>> ---
>>   include/linux/mm_types.h |  2 ++
>>   kernel/sched/fair.c      | 32 ++++++++++++++++++++++++++++++++
>>   mm/memory.c              | 21 +++++++++++++++++++++
>>   3 files changed, 55 insertions(+)
>>
>> diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
>> index 500e536796ca..07feae37b8e6 100644
>> --- a/include/linux/mm_types.h
>> +++ b/include/linux/mm_types.h
>> @@ -506,6 +506,8 @@ struct vm_area_struct {
>>       struct mempolicy *vm_policy;    /* NUMA policy for the VMA */
>>   #endif
>>       struct vm_userfaultfd_ctx vm_userfaultfd_ctx;
>> +    unsigned int accessing_pids;
>> +    int next_pid_slot;
>>   } __randomize_layout;
> 
> What immediately jumps at me is the unconditional grow of a VMA by 8 
> bytes. A process with 64k mappings consumes 512 KiB more of memory, 
> possibly completely unnecessarily.
> 
> This at least needs to be fenced by CONFIG_NUMA_BALANCING.
> 

Thanks for the review David. Good point..  I do agree. I see I will have
to fence further in memory.c only since fair.c is already taken care.