Re: [PATCH 1/8] mm/migrate.c: skip node check if done in last round

[Wei Yang <richardw.yang@linux.intel.com>]

On Tue, Jan 21, 2020 at 09:42:05AM +0100, Michal Hocko wrote:
>On Tue 21-01-20 06:25:40, Wei Yang wrote:
>> On Mon, Jan 20, 2020 at 10:36:46AM +0100, Michal Hocko wrote:
>> >On Sun 19-01-20 11:06:29, Wei Yang wrote:
>> >> Before move page to target node, we would check if the node id is valid.
>> >> In case we would try to move pages to the same target node, it is not
>> >> necessary to do the check each time.
>> >> 
>> >> This patch tries to skip the check if the node has been checked.
>> >> 
>> >> Signed-off-by: Wei Yang <richardw.yang@linux.intel.com>
>> >> ---
>> >>  mm/migrate.c | 19 +++++++++++--------
>> >>  1 file changed, 11 insertions(+), 8 deletions(-)
>> >> 
>> >> diff --git a/mm/migrate.c b/mm/migrate.c
>> >> index 430fdccc733e..ba7cf4fa43a0 100644
>> >> --- a/mm/migrate.c
>> >> +++ b/mm/migrate.c
>> >> @@ -1612,15 +1612,18 @@ static int do_pages_move(struct mm_struct *mm, nodemask_t task_nodes,
>> >>  			goto out_flush;
>> >>  		addr = (unsigned long)untagged_addr(p);
>> >>  
>> >> -		err = -ENODEV;
>> >> -		if (node < 0 || node >= MAX_NUMNODES)
>> >> -			goto out_flush;
>> >> -		if (!node_state(node, N_MEMORY))
>> >> -			goto out_flush;
>> >> +		/* Check node if it is not checked. */
>> >> +		if (current_node == NUMA_NO_NODE || node != current_node) {
>> >> +			err = -ENODEV;
>> >> +			if (node < 0 || node >= MAX_NUMNODES)
>> >> +				goto out_flush;
>> >> +			if (!node_state(node, N_MEMORY))
>> >> +				goto out_flush;
>> >
>> >This makes the code harder to read IMHO. The original code checks the
>> >valid node first and it doesn't conflate that with the node caching
>> >logic which your change does.
>> >
>> 
>> I am sorry, would you mind showing me an example about the conflate in my
>> change? I don't get it.
>
>NUMA_NO_NODE is the iteration logic, right? It resets the batching node.
>Node check read from the userspace is an input sanitization. Do not put
>those two into the same checks. More clear now?

Yes, I see your point.

Can we think like this:

  On each iteration, we do an input sanitization?

Well, this is a trivial one. If you don't like it, I would remove this.

>-- 
>Michal Hocko
>SUSE Labs

-- 
Wei Yang
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