linux-kernel - Re: [PATCH 4/4] mm/swapfile.c: move new_cluster to check free

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Date:   Mon, 20 Apr 2020 21:45:17 +0000
From:   Wei Yang <richard.weiyang@...il.com>
To:     "Huang, Ying" <ying.huang@...el.com>
Cc:     Wei Yang <richard.weiyang@...il.com>, akpm@...ux-foundation.org,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        tim.c.chen@...ux.intel.com
Subject: Re: [PATCH 4/4] mm/swapfile.c: move new_cluster to check
 free_clusters directly

On Mon, Apr 20, 2020 at 09:41:43AM +0800, Huang, Ying wrote:
>Wei Yang <richard.weiyang@...il.com> writes:
>
>> Each time it needs jump to new_cluster, it is sure current
>> percpu_cluster is null.
>>
>> Move the new_cluster to check free_clusters directly.
>>
>> Signed-off-by: Wei Yang <richard.weiyang@...il.com>
>> ---
>>  mm/swapfile.c | 2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/mm/swapfile.c b/mm/swapfile.c
>> index 07b0bc095411..78e92ff14c79 100644
>> --- a/mm/swapfile.c
>> +++ b/mm/swapfile.c
>> @@ -603,9 +603,9 @@ static bool scan_swap_map_try_ssd_cluster(struct swap_info_struct *si,
>>  	struct swap_cluster_info *ci;
>>  	unsigned long tmp, max;
>>  
>> -new_cluster:
>>  	cluster = this_cpu_ptr(si->percpu_cluster);
>>  	if (cluster_is_null(&cluster->index)) {
>> +new_cluster:
>>  		if (!cluster_list_empty(&si->free_clusters)) {
>>  			cluster->index = si->free_clusters.head;
>>  			cluster->next = cluster_next(&cluster->index) *
>
>In swap_do_scheduled_discard(), we will unlock si->lock, so the
>percpu_cluster may be changed after we releasing the lock.  Or the
>current thread may be moved to a different CPU.

Thanks, you are right.

>
>Best Regards,
>Huang, Ying

-- 
Wei Yang
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