Re: [PATCH] mm/hotplug: Enumerate memory range offlining failure reasons

[Michal Hocko]

On Tue 18-08-20 09:52:02, Anshuman Khandual wrote:
> Currently a debug message is printed describing the reason for memory range
> offline failure. This just enumerates existing reason codes which improves
> overall readability and makes it cleaner. This does not add any functional
> change.

Wasn't something like that posted already? To be honest I do not think
this is worth the additional LOC. We are talking about few strings used
at a single place. I really do not see any simplification, constants are
sometimes even longer than the strings they are describing.

> Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> Cc: David Hildenbrand <david@xxxxxxxxxx>
> Cc: Michal Hocko <mhocko@xxxxxxxx>
> Cc: Dan Williams <dan.j.williams@xxxxxxxxx>
> Cc: linux-mm@xxxxxxxxx
> Cc: linux-kernel@xxxxxxxxxxxxxxx
> Signed-off-by: Anshuman Khandual <anshuman.khandual@xxxxxxx>
> ---
> This is based on 5.9-rc1
> 
>  include/linux/memory.h | 28 ++++++++++++++++++++++++++++
>  mm/memory_hotplug.c    | 18 +++++++++---------
>  2 files changed, 37 insertions(+), 9 deletions(-)
> 
> diff --git a/include/linux/memory.h b/include/linux/memory.h
> index 439a89e758d8..4b52d706edc1 100644
> --- a/include/linux/memory.h
> +++ b/include/linux/memory.h
> @@ -44,6 +44,34 @@ int set_memory_block_size_order(unsigned int order);
>  #define	MEM_CANCEL_ONLINE	(1<<4)
>  #define	MEM_CANCEL_OFFLINE	(1<<5)
>  
> +/*
> + * Memory offline failure reasons
> + */
> +enum offline_failure_reason {
> +	OFFLINE_FAILURE_MEMHOLES,
> +	OFFLINE_FAILURE_MULTIZONE,
> +	OFFLINE_FAILURE_ISOLATE,
> +	OFFLINE_FAILURE_NOTIFIER,
> +	OFFLINE_FAILURE_SIGNAL,
> +	OFFLINE_FAILURE_UNMOVABLE,
> +	OFFLINE_FAILURE_DISSOLVE,
> +};
> +
> +static const char *const offline_failure_names[] = {
> +	[OFFLINE_FAILURE_MEMHOLES]	= "memory holes",
> +	[OFFLINE_FAILURE_MULTIZONE]	= "multizone range",
> +	[OFFLINE_FAILURE_ISOLATE]	= "failure to isolate range",
> +	[OFFLINE_FAILURE_NOTIFIER]	= "notifier failure",
> +	[OFFLINE_FAILURE_SIGNAL]	= "signal backoff",
> +	[OFFLINE_FAILURE_UNMOVABLE]	= "unmovable page",
> +	[OFFLINE_FAILURE_DISSOLVE]	= "failure to dissolve huge pages",
> +};
> +
> +static inline const char *offline_failure(enum offline_failure_reason reason)
> +{
> +	return offline_failure_names[reason];
> +}
> +
>  struct memory_notify {
>  	unsigned long start_pfn;
>  	unsigned long nr_pages;
> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
> index e9d5ab5d3ca0..b3fa36a09d7f 100644
> --- a/mm/memory_hotplug.c
> +++ b/mm/memory_hotplug.c
> @@ -1484,7 +1484,7 @@ static int __ref __offline_pages(unsigned long start_pfn,
>  	unsigned long flags;
>  	struct zone *zone;
>  	struct memory_notify arg;
> -	char *reason;
> +	enum offline_failure_reason reason;
>  
>  	mem_hotplug_begin();
>  
> @@ -1500,7 +1500,7 @@ static int __ref __offline_pages(unsigned long start_pfn,
>  			      count_system_ram_pages_cb);
>  	if (nr_pages != end_pfn - start_pfn) {
>  		ret = -EINVAL;
> -		reason = "memory holes";
> +		reason = OFFLINE_FAILURE_MEMHOLES;
>  		goto failed_removal;
>  	}
>  
> @@ -1509,7 +1509,7 @@ static int __ref __offline_pages(unsigned long start_pfn,
>  	zone = test_pages_in_a_zone(start_pfn, end_pfn);
>  	if (!zone) {
>  		ret = -EINVAL;
> -		reason = "multizone range";
> +		reason = OFFLINE_FAILURE_MULTIZONE;
>  		goto failed_removal;
>  	}
>  	node = zone_to_nid(zone);
> @@ -1519,7 +1519,7 @@ static int __ref __offline_pages(unsigned long start_pfn,
>  				       MIGRATE_MOVABLE,
>  				       MEMORY_OFFLINE | REPORT_FAILURE);
>  	if (ret < 0) {
> -		reason = "failure to isolate range";
> +		reason = OFFLINE_FAILURE_ISOLATE;
>  		goto failed_removal;
>  	}
>  	nr_isolate_pageblock = ret;
> @@ -1531,7 +1531,7 @@ static int __ref __offline_pages(unsigned long start_pfn,
>  	ret = memory_notify(MEM_GOING_OFFLINE, &arg);
>  	ret = notifier_to_errno(ret);
>  	if (ret) {
> -		reason = "notifier failure";
> +		reason = OFFLINE_FAILURE_NOTIFIER;
>  		goto failed_removal_isolated;
>  	}
>  
> @@ -1540,7 +1540,7 @@ static int __ref __offline_pages(unsigned long start_pfn,
>  		do {
>  			if (signal_pending(current)) {
>  				ret = -EINTR;
> -				reason = "signal backoff";
> +				reason = OFFLINE_FAILURE_SIGNAL;
>  				goto failed_removal_isolated;
>  			}
>  
> @@ -1558,7 +1558,7 @@ static int __ref __offline_pages(unsigned long start_pfn,
>  		} while (!ret);
>  
>  		if (ret != -ENOENT) {
> -			reason = "unmovable page";
> +			reason = OFFLINE_FAILURE_UNMOVABLE;
>  			goto failed_removal_isolated;
>  		}
>  
> @@ -1569,7 +1569,7 @@ static int __ref __offline_pages(unsigned long start_pfn,
>  		 */
>  		ret = dissolve_free_huge_pages(start_pfn, end_pfn);
>  		if (ret) {
> -			reason = "failure to dissolve huge pages";
> +			reason = OFFLINE_FAILURE_DISSOLVE;
>  			goto failed_removal_isolated;
>  		}
>  		/* check again */
> @@ -1627,7 +1627,7 @@ static int __ref __offline_pages(unsigned long start_pfn,
>  	pr_debug("memory offlining [mem %#010llx-%#010llx] failed due to %s\n",
>  		 (unsigned long long) start_pfn << PAGE_SHIFT,
>  		 ((unsigned long long) end_pfn << PAGE_SHIFT) - 1,
> -		 reason);
> +		 offline_failure(reason));
>  	/* pushback to free area */
>  	mem_hotplug_done();
>  	return ret;
> -- 
> 2.20.1
> 

-- 
Michal Hocko
SUSE Labs