linux-kernel - Re: [RFC PATCH 1/3] memory tiering: read last_cpupid correctly in do_huge_pmd_numa

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Message-ID: <bd6459a5-5bfd-4986-b110-6b8af1e0eda8@linux.alibaba.com>
Date: Fri, 12 Jul 2024 12:01:20 +0800
From: Baolin Wang <baolin.wang@...ux.alibaba.com>
To: Zi Yan <ziy@...dia.com>, David Hildenbrand <david@...hat.com>,
 "Huang, Ying" <ying.huang@...el.com>, linux-mm@...ck.org
Cc: Andrew Morton <akpm@...ux-foundation.org>, linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH 1/3] memory tiering: read last_cpupid correctly in
 do_huge_pmd_numa_page()



On 2024/7/12 10:44, Zi Yan wrote:
> From: Zi Yan <ziy@...dia.com>
> 
> last_cpupid is only available when memory tiering is off or the folio
> is in toptier node. Complete the check to read last_cpupid when it is
> available.
> 
> Before the fix, the default last_cpupid will be used even if memory
> tiering mode is turned off at runtime instead of the actual value. This
> can prevent task_numa_fault() from getting right numa fault stats, but
> should not cause any crash. User might see performance changes after the
> fix.
> 
> Fixes: 33024536bafd ("memory tiering: hot page selection with hint page fault latency")
> Signed-off-by: Zi Yan <ziy@...dia.com>

LGTM.
Reviewed-by: Baolin Wang <baolin.wang@...ux.alibaba.com>

> ---
>   mm/huge_memory.c | 3 ++-
>   1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
> index d7c84480f1a4..07d9dde4ca33 100644
> --- a/mm/huge_memory.c
> +++ b/mm/huge_memory.c
> @@ -1705,7 +1705,8 @@ vm_fault_t do_huge_pmd_numa_page(struct vm_fault *vmf)
>   	 * For memory tiering mode, cpupid of slow memory page is used
>   	 * to record page access time.  So use default value.
>   	 */
> -	if (node_is_toptier(nid))
> +	if (!(sysctl_numa_balancing_mode & NUMA_BALANCING_MEMORY_TIERING) ||
> +	    node_is_toptier(nid))
>   		last_cpupid = folio_last_cpupid(folio);
>   	target_nid = numa_migrate_prep(folio, vmf, haddr, nid, &flags);
>   	if (target_nid == NUMA_NO_NODE)