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From:   "Huang, Ying" <ying.huang@intel.com>
To:     Oscar Salvador <osalvador@suse.de>
Cc:     Peter Zijlstra <peterz@infradead.org>,
        Mel Gorman <mgorman@techsingularity.net>,
        Andrew Morton <akpm@linux-foundation.org>, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org, Feng Tang <feng.tang@intel.com>,
        Baolin Wang <baolin.wang@linux.alibaba.com>,
        Michal Hocko <mhocko@suse.com>,
        Rik van Riel <riel@surriel.com>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        Yang Shi <shy828301@gmail.com>, Zi Yan <ziy@nvidia.com>,
        Wei Xu <weixugc@google.com>,
        Shakeel Butt <shakeelb@google.com>,
        zhongjiang-ali <zhongjiang-ali@linux.alibaba.com>,
        Randy Dunlap <rdunlap@infradead.org>,
        Johannes Weiner <hannes@cmpxchg.org>
Subject: Re: [PATCH -V13 2/3] NUMA balancing: optimize page placement for
 memory tiering system
References: <20220221084529.1052339-1-ying.huang@intel.com>
        <20220221084529.1052339-3-ying.huang@intel.com>
        <YhzwO/lw1xx7EjNb@localhost.localdomain>
        <87czj6321p.fsf@yhuang6-desk2.ccr.corp.intel.com>
        <Yh26v+4LtnvFnWWz@localhost.localdomain>
Date:   Tue, 01 Mar 2022 14:40:44 +0800
In-Reply-To: <Yh26v+4LtnvFnWWz@localhost.localdomain> (Oscar Salvador's
        message of "Tue, 1 Mar 2022 07:18:39 +0100")
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Oscar Salvador <osalvador@suse.de> writes:

> On Tue, Mar 01, 2022 at 09:16:18AM +0800, Huang, Ying wrote:
>> Hi, Oscar,
>
> Hi Huang Ying
>
>>  b. Make kswapd of the fast memory node to reclaim pages until the free
>>     pages are a little more than the high watermark (named as promo
>>     watermark).  If we want to promote some hot pages from the slow
>>     memory to the fast memory, but the free pages of the fast memory
>>     node will become lower than the high watermark after promotion, we
>>     will wake up kswapd of the fast memory node to demote more cold
>>     pages in the fast memory node to the slow memory node firstly.  This
>>     will free some extra space in the fast memory node, so the hot pages
>>     in the slow memory node can be promoted to the fast memory node.
>
> What about this? Somehow it sounds clear to me.
>
> "b. Define a new watermark called wmark_promo which is higher than wmark_high,
>     and have kswapd reclaiming pages until free pages reach such watermark.
>     The scenario is as follows: when we want to promote hot-pages from a slow
>     memory to a fast memory, but fast memory's free pages would go lower than
>     high watermark with such promotion, we wake up kswapd with wmark_promo
>     watermark in order to demote cold pages and free us up some space.
>     So, next time we want to promote hot-pages we might have a chance of
>     doing so."

Your version looks better.  I will use it.  Thanks!

> But I am fine with your updated write up as well, so if you spin a new
> version:
>
> Reviewed-by: Oscar Salvador <osalvador@suse.de>

Thanks!

Best Regards,
Huang, Ying