[PATCH] dax/kmem: Pass valid argument to memory_group_register_static

[PATCH] dax/kmem: Pass valid argument to memory_group_register_static

[Tarun Sahu]

memory_group_register_static takes maximum number of pages as the argument
while dev_dax_kmem_probe passes total_len (in bytes) as the argument.

Signed-off-by: Tarun Sahu <tsahu@linux.ibm.com>
---
 drivers/dax/kmem.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/dax/kmem.c b/drivers/dax/kmem.c
index 7b36db6f1cbd..898ca9505754 100644
--- a/drivers/dax/kmem.c
+++ b/drivers/dax/kmem.c
@@ -99,7 +99,7 @@ static int dev_dax_kmem_probe(struct dev_dax *dev_dax)
 	if (!data->res_name)
 		goto err_res_name;
 
-	rc = memory_group_register_static(numa_node, total_len);
+	rc = memory_group_register_static(numa_node, PFN_UP(total_len));
 	if (rc < 0)
 		goto err_reg_mgid;
 	data->mgid = rc;
-- 
2.31.1

Re: [PATCH] dax/kmem: Pass valid argument to memory_group_register_static

[Alison Schofield]

On Tue, Jun 20, 2023 at 07:33:32PM +0530, Tarun Sahu wrote:
> memory_group_register_static takes maximum number of pages as the argument
> while dev_dax_kmem_probe passes total_len (in bytes) as the argument.

This sounds like a fix. An explanation of the impact and a fixes tag
may be needed. Also, wondering how you found it.

Alison

> 
> Signed-off-by: Tarun Sahu <tsahu@linux.ibm.com>
> ---
>  drivers/dax/kmem.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/dax/kmem.c b/drivers/dax/kmem.c
> index 7b36db6f1cbd..898ca9505754 100644
> --- a/drivers/dax/kmem.c
> +++ b/drivers/dax/kmem.c
> @@ -99,7 +99,7 @@ static int dev_dax_kmem_probe(struct dev_dax *dev_dax)
>  	if (!data->res_name)
>  		goto err_res_name;
>  
> -	rc = memory_group_register_static(numa_node, total_len);
> +	rc = memory_group_register_static(numa_node, PFN_UP(total_len));
>  	if (rc < 0)
>  		goto err_reg_mgid;
>  	data->mgid = rc;
> -- 
> 2.31.1
> 

Re: [PATCH] dax/kmem: Pass valid argument to memory_group_register_static

[Tarun Sahu]

Hi Alison,

Alison Schofield <alison.schofield@intel.com> writes:

> On Tue, Jun 20, 2023 at 07:33:32PM +0530, Tarun Sahu wrote:
>> memory_group_register_static takes maximum number of pages as the argument
>> while dev_dax_kmem_probe passes total_len (in bytes) as the argument.
>
> This sounds like a fix. An explanation of the impact and a fixes tag
> may be needed. Also, wondering how you found it.
>
Yes, it is a fix, I found it during dry code walk-through.
There is not any impact as such. As,
memory_group_register_static just set the max_pages limit which
is used in auto_movable_zone_for_pfn to determine the zone.

which might cause these condition to behave differently,

This will be true always so jump will happen to kernel_zone
	if (!auto_movable_can_online_movable(NUMA_NO_NODE, group, nr_pages))
		goto kernel_zone;
---
kernel_zone:
	return default_kernel_zone_for_pfn(nid, pfn, nr_pages);

---

Here, In below, zone_intersects compare range will be larger as nr_pages
will be higher (derived from total_len passed in dev_dax_kmem_probe).

static struct zone *default_kernel_zone_for_pfn(int nid, unsigned long start_pfn,
		unsigned long nr_pages)
{
	struct pglist_data *pgdat = NODE_DATA(nid);
	int zid;

	for (zid = 0; zid < ZONE_NORMAL; zid++) {
		struct zone *zone = &pgdat->node_zones[zid];

		if (zone_intersects(zone, start_pfn, nr_pages))
			return zone;
	}

	return &pgdat->node_zones[ZONE_NORMAL];
}

In Mostly cases, ZONE_NORMAL will be returned. But there is no
crash/panic issues involved here, only decision making on selecting zone
is affected.



> Alison
>
>> 
>> Signed-off-by: Tarun Sahu <tsahu@linux.ibm.com>
>> ---
>>  drivers/dax/kmem.c | 2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>> 
>> diff --git a/drivers/dax/kmem.c b/drivers/dax/kmem.c
>> index 7b36db6f1cbd..898ca9505754 100644
>> --- a/drivers/dax/kmem.c
>> +++ b/drivers/dax/kmem.c
>> @@ -99,7 +99,7 @@ static int dev_dax_kmem_probe(struct dev_dax *dev_dax)
>>  	if (!data->res_name)
>>  		goto err_res_name;
>>  
>> -	rc = memory_group_register_static(numa_node, total_len);
>> +	rc = memory_group_register_static(numa_node, PFN_UP(total_len));
>>  	if (rc < 0)
>>  		goto err_reg_mgid;
>>  	data->mgid = rc;
>> -- 
>> 2.31.1
>> 

Re: [PATCH] dax/kmem: Pass valid argument to memory_group_register_static

[Verma, Vishal L]

On Wed, 2023-06-21 at 11:36 +0530, Tarun Sahu wrote:
> Hi Alison,
> 
> Alison Schofield <alison.schofield@intel.com> writes:
> 
> > On Tue, Jun 20, 2023 at 07:33:32PM +0530, Tarun Sahu wrote:
> > > memory_group_register_static takes maximum number of pages as the argument
> > > while dev_dax_kmem_probe passes total_len (in bytes) as the argument.
> > 
> > This sounds like a fix. An explanation of the impact and a fixes tag
> > may be needed. Also, wondering how you found it.
> > 
> Yes, it is a fix, I found it during dry code walk-through.
> There is not any impact as such. As,
> memory_group_register_static just set the max_pages limit which
> is used in auto_movable_zone_for_pfn to determine the zone.
> 
> which might cause these condition to behave differently,
> 
> This will be true always so jump will happen to kernel_zone
>         if (!auto_movable_can_online_movable(NUMA_NO_NODE, group, nr_pages))
>                 goto kernel_zone;
> ---
> kernel_zone:
>         return default_kernel_zone_for_pfn(nid, pfn, nr_pages);
> 
> ---
> 
> Here, In below, zone_intersects compare range will be larger as nr_pages
> will be higher (derived from total_len passed in dev_dax_kmem_probe).
> 
> static struct zone *default_kernel_zone_for_pfn(int nid, unsigned long start_pfn,
>                 unsigned long nr_pages)
> {
>         struct pglist_data *pgdat = NODE_DATA(nid);
>         int zid;
> 
>         for (zid = 0; zid < ZONE_NORMAL; zid++) {
>                 struct zone *zone = &pgdat->node_zones[zid];
> 
>                 if (zone_intersects(zone, start_pfn, nr_pages))
>                         return zone;
>         }
> 
>         return &pgdat->node_zones[ZONE_NORMAL];
> }
> 
> In Mostly cases, ZONE_NORMAL will be returned. But there is no
> crash/panic issues involved here, only decision making on selecting zone
> is affected.
> 

Hi Tarun,

Good find! With a Fixes tag, and perhaps inclusion of a bit more of
this detail described in the commit message, feel free to add:

Reviewed-by: Vishal Verma <vishal.l.verma@intel.com>

Re: [PATCH] dax/kmem: Pass valid argument to memory_group_register_static

[Tarun Sahu]

Hi Vishal,

"Verma, Vishal L" <vishal.l.verma@intel.com> writes:

> On Wed, 2023-06-21 at 11:36 +0530, Tarun Sahu wrote:
>> Hi Alison,
>> 
>> Alison Schofield <alison.schofield@intel.com> writes:
>> 
>> > On Tue, Jun 20, 2023 at 07:33:32PM +0530, Tarun Sahu wrote:
>> > > memory_group_register_static takes maximum number of pages as the argument
>> > > while dev_dax_kmem_probe passes total_len (in bytes) as the argument.
>> > 
>> > This sounds like a fix. An explanation of the impact and a fixes tag
>> > may be needed. Also, wondering how you found it.
>> > 
>> Yes, it is a fix, I found it during dry code walk-through.
>> There is not any impact as such. As,
>> memory_group_register_static just set the max_pages limit which
>> is used in auto_movable_zone_for_pfn to determine the zone.
>> 
>> which might cause these condition to behave differently,
>> 
>> This will be true always so jump will happen to kernel_zone
>>         if (!auto_movable_can_online_movable(NUMA_NO_NODE, group, nr_pages))
>>                 goto kernel_zone;
>> ---
>> kernel_zone:
>>         return default_kernel_zone_for_pfn(nid, pfn, nr_pages);
>> 
>> ---
>> 
>> Here, In below, zone_intersects compare range will be larger as nr_pages
>> will be higher (derived from total_len passed in dev_dax_kmem_probe).
>> 
>> static struct zone *default_kernel_zone_for_pfn(int nid, unsigned long start_pfn,
>>                 unsigned long nr_pages)
>> {
>>         struct pglist_data *pgdat = NODE_DATA(nid);
>>         int zid;
>> 
>>         for (zid = 0; zid < ZONE_NORMAL; zid++) {
>>                 struct zone *zone = &pgdat->node_zones[zid];
>> 
>>                 if (zone_intersects(zone, start_pfn, nr_pages))
>>                         return zone;
>>         }
>> 
>>         return &pgdat->node_zones[ZONE_NORMAL];
>> }
>> 
>> In Mostly cases, ZONE_NORMAL will be returned. But there is no
>> crash/panic issues involved here, only decision making on selecting zone
>> is affected.
>> 
>
> Hi Tarun,
>
> Good find! With a Fixes tag, and perhaps inclusion of a bit more of
> this detail described in the commit message, feel free to add:
>
Thanks for reviewing, sent the updated version.

> Reviewed-by: Vishal Verma <vishal.l.verma@intel.com>