linux-kernel - Re: [PATCH v4 10/11] mm/memory-failure: remove a wrapper for alloc_migration

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Date:   Tue, 7 Jul 2020 17:03:50 +0200
From:   Vlastimil Babka <vbabka@...e.cz>
To:     Michal Hocko <mhocko@...nel.org>, js1304@...il.com
Cc:     Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, kernel-team@....com,
        Christoph Hellwig <hch@...radead.org>,
        Roman Gushchin <guro@...com>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        Naoya Horiguchi <n-horiguchi@...jp.nec.com>,
        Joonsoo Kim <iamjoonsoo.kim@....com>
Subject: Re: [PATCH v4 10/11] mm/memory-failure: remove a wrapper for
 alloc_migration_target()

On 7/7/20 1:48 PM, Michal Hocko wrote:
> On Tue 07-07-20 16:44:48, Joonsoo Kim wrote:
>> From: Joonsoo Kim <iamjoonsoo.kim@....com>
>> 
>> There is a well-defined standard migration target callback. Use it
>> directly.
>> 
>> Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@....com>
>> ---
>>  mm/memory-failure.c | 18 ++++++------------
>>  1 file changed, 6 insertions(+), 12 deletions(-)
>> 
>> diff --git a/mm/memory-failure.c b/mm/memory-failure.c
>> index 609d42b6..3b89804 100644
>> --- a/mm/memory-failure.c
>> +++ b/mm/memory-failure.c
>> @@ -1677,16 +1677,6 @@ int unpoison_memory(unsigned long pfn)
>>  }
>>  EXPORT_SYMBOL(unpoison_memory);
>>  
>> -static struct page *new_page(struct page *p, unsigned long private)
>> -{
>> -	struct migration_target_control mtc = {
>> -		.nid = page_to_nid(p),
>> -		.gfp_mask = GFP_USER | __GFP_MOVABLE | __GFP_RETRY_MAYFAIL,
>> -	};
>> -
>> -	return alloc_migration_target(p, (unsigned long)&mtc);
>> -}
>> -
>>  /*
>>   * Safely get reference count of an arbitrary page.
>>   * Returns 0 for a free page, -EIO for a zero refcount page
>> @@ -1793,6 +1783,10 @@ static int __soft_offline_page(struct page *page)
>>  	const char *msg_page[] = {"page", "hugepage"};
>>  	bool huge = PageHuge(page);
>>  	LIST_HEAD(pagelist);
>> +	struct migration_target_control mtc = {
>> +		.nid = NUMA_NO_NODE,
>> +		.gfp_mask = GFP_USER | __GFP_MOVABLE | __GFP_RETRY_MAYFAIL,
>> +	};
> 
> Is NUMA_NO_NODE really intended here? The original code has preferred to
> stay on the same node.

The alloc_migration_target() interprets NUMA_NO_NODE as a request to call
page_to_nid(), so we don't need these thin wrappers that do just that. I have
suggested this in v3 review and it's mentioned in 06/11.

> If this is intentional then the changelog should
> be explicit about that.
> 
>>  
>>  	/*
>>  	 * Check PageHWPoison again inside page lock because PageHWPoison
>> @@ -1829,8 +1823,8 @@ static int __soft_offline_page(struct page *page)
>>  	}
>>  
>>  	if (isolate_page(hpage, &pagelist)) {
>> -		ret = migrate_pages(&pagelist, new_page, NULL, MPOL_MF_MOVE_ALL,
>> -					MIGRATE_SYNC, MR_MEMORY_FAILURE);
>> +		ret = migrate_pages(&pagelist, alloc_migration_target, NULL,
>> +			(unsigned long)&mtc, MIGRATE_SYNC, MR_MEMORY_FAILURE);
>>  		if (!ret) {
>>  			bool release = !huge;
>>  
>> -- 
>> 2.7.4
>> 
>