Re: [PATCH -V12 1/3] NUMA Balancing: add page promotion counter

From: Oscar Salvador <osalvador@suse.de>
To: Huang Ying <ying.huang@intel.com>
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>, Yang Shi <shy828301@gmail.com>,
	Baolin Wang <baolin.wang@linux.alibaba.com>,
	Johannes Weiner <hannes@cmpxchg.org>,
	Michal Hocko <mhocko@suse.com>, Rik van Riel <riel@surriel.com>,
	Dave Hansen <dave.hansen@linux.intel.com>,
	Zi Yan <ziy@nvidia.com>, Wei Xu <weixugc@google.com>,
	Shakeel Butt <shakeelb@google.com>,
	zhongjiang-ali <zhongjiang-ali@linux.alibaba.com>
Subject: Re: [PATCH -V12 1/3] NUMA Balancing: add page promotion counter
Date: Wed, 16 Feb 2022 09:49:02 +0100	[thread overview]
Message-ID: <Ygy6fg/KOTikCgLW@localhost.localdomain> (raw)
In-Reply-To: <20220216073815.2505536-2-ying.huang@intel.com>

On Wed, Feb 16, 2022 at 03:38:13PM +0800, Huang Ying wrote:
> In a system with multiple memory types, e.g. DRAM and PMEM, the CPU
> and DRAM in one socket will be put in one NUMA node as before, while
> the PMEM will be put in another NUMA node as described in the
> description of the commit c221c0b0308f ("device-dax: "Hotplug"
> persistent memory for use like normal RAM").  So, the NUMA balancing
> mechanism will identify all PMEM accesses as remote access and try to
> promote the PMEM pages to DRAM.
> 
> To distinguish the number of the inter-type promoted pages from that
> of the inter-socket migrated pages.  A new vmstat count is added.  The
> counter is per-node (count in the target node).  So this can be used
> to identify promotion imbalance among the NUMA nodes.
> 
> Signed-off-by: "Huang, Ying" <ying.huang@intel.com>
> Reviewed-by: Yang Shi <shy828301@gmail.com>
> Tested-by: Baolin Wang <baolin.wang@linux.alibaba.com>
> Reviewed-by: Baolin Wang <baolin.wang@linux.alibaba.com>
> Acked-by: Johannes Weiner <hannes@cmpxchg.org>
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Cc: Michal Hocko <mhocko@suse.com>
> Cc: Rik van Riel <riel@surriel.com>
> Cc: Mel Gorman <mgorman@techsingularity.net>
> Cc: Peter Zijlstra <peterz@infradead.org>
> Cc: Dave Hansen <dave.hansen@linux.intel.com>
> Cc: Zi Yan <ziy@nvidia.com>
> Cc: Wei Xu <weixugc@google.com>
> Cc: osalvador <osalvador@suse.de>
> Cc: Shakeel Butt <shakeelb@google.com>
> Cc: zhongjiang-ali <zhongjiang-ali@linux.alibaba.com>
> Cc: linux-kernel@vger.kernel.org
> Cc: linux-mm@kvack.org
> ---
...

> @@ -2072,6 +2072,7 @@ int migrate_misplaced_page(struct page *page, struct vm_area_struct *vma,
>  	pg_data_t *pgdat = NODE_DATA(node);
>  	int isolated;
>  	int nr_remaining;
> +	int nr_succeeded;

I think we should make this consistent and make it "unsigned int".
That is what migrate_pages() expects, and what the other caller using
nr_succeeded (demote_page_list()) already uses.
Unless there is a strong reason not to do so.

Reviewed-by: Oscar Salvador <osalvador@suse.de>

-- 
Oscar Salvador
SUSE Labs