linux-kernel - Re: [PATCH 0/4] Extend migrate_misplaced

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Message-ID: <9749af5b-8c0b-49e4-d76e-129736472499@linux.alibaba.com>
Date:   Mon, 21 Aug 2023 16:50:10 +0800
From:   Baolin Wang <baolin.wang@...ux.alibaba.com>
To:     "Huang, Ying" <ying.huang@...el.com>
Cc:     akpm@...ux-foundation.org, mgorman@...hsingularity.net,
        shy828301@...il.com, david@...hat.com, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/4] Extend migrate_misplaced_page() to support batch
 migration



On 8/21/2023 4:41 PM, Huang, Ying wrote:
> Baolin Wang <baolin.wang@...ux.alibaba.com> writes:
> 
>> On 8/21/2023 10:29 AM, Huang, Ying wrote:
>>> Baolin Wang <baolin.wang@...ux.alibaba.com> writes:
>>>
>>>> Hi,
>>>>
>>>> Currently, on our ARM servers with NUMA enabled, we found the cross-die latency
>>>> is a little larger that will significantly impact the workload's performance.
>>>> So on ARM servers we will rely on the NUMA balancing to avoid the cross-die
>>>> accessing. And I posted a patchset[1] to support speculative numa fault to
>>>> improve the NUMA balancing's performance according to the principle of data
>>>> locality. Moreover, thanks to Huang Ying's patchset[2], which introduced batch
>>>> migration as a way to reduce the cost of TLB flush, and it will also benefit
>>>> the migration of multiple pages all at once during NUMA balancing.
>>>>
>>>> So we plan to continue to support batch migration in do_numa_page() to improve
>>>> the NUMA balancing's performance, but before adding complicated batch migration
>>>> algorithm for NUMA balancing, some cleanup and preparation work need to do firstly,
>>>> which are done in this patch set. In short, this patchset extends the
>>>> migrate_misplaced_page() interface to support batch migration, and no functional
>>>> changes intended.
>>> Will these cleanup benefit anything except batching migration?  If
>>> not,
>>
>> I hope these cleanup can also benefit the compound page's NUMA
>> balancing, which was discussed in the thread[1]. IIUC, for the
>> compound page's NUMA balancing, it is possible that partial pages were
>> successfully migrated, so it is necessary to return the number of
>> pages that were successfully migrated from
>> migrate_misplaced_page(). (But I did not look this in detail yet,
>> please correct me if I missed something, and I will find some time to
>> look this in detail). That is why I think these cleanups are
>> straightforward.
>>
>> Yes, I will post the batch migration patches after more polish and
>> testing, but I think these cleanups are separate and straightforward,
>> so I plan to submit the patches separately.
> 
> Then, please state the benefit explicitly in the patch description
> instead of just preparation for batching migration.

Sure, will do. Thanks.