[PATCH v2 0/2] mm/memory_hotplug: cleanup do_migrate_range()

[PATCH v2 0/2] mm/memory_hotplug: cleanup do_migrate_range()

[SeongJae Park]

Make do_migrate_range() return value mechanism simple.

Changes from v1
(https://lore.kernel.org/linux-mm/20230214223236.58430-1-sj@kernel.org/)
- Simply return nothing from do_migrate_range() (David Hildenbrand)
- Add a cleanup for 'ret' variable

SeongJae Park (2):
  mm/memory_hotplug: return nothing from do_migrate_range()
  mm/memory_hotplug: cleanup 'ret' variable usage in do_migrate_range()

 mm/memory_hotplug.c | 8 ++------
 1 file changed, 2 insertions(+), 6 deletions(-)

-- 
2.25.1

[PATCH v2 1/2] mm/memory_hotplug: return nothing from do_migrate_range()

[SeongJae Park]

Return value mechanism of do_migrate_range() is not very simple, while
no caller of the function checks the return value.  Make the function
return nothing to be more simple.

Suggested-by: David Hildenbrand <david@redhat.com>
Signed-off-by: SeongJae Park <sj@kernel.org>
---
 mm/memory_hotplug.c | 5 +----
 1 file changed, 1 insertion(+), 4 deletions(-)

diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
index bcb0dc41c2f2..6c615ba1a5c7 100644
--- a/mm/memory_hotplug.c
+++ b/mm/memory_hotplug.c
@@ -1620,8 +1620,7 @@ static int scan_movable_pages(unsigned long start, unsigned long end,
 	return 0;
 }
 
-static int
-do_migrate_range(unsigned long start_pfn, unsigned long end_pfn)
+static void do_migrate_range(unsigned long start_pfn, unsigned long end_pfn)
 {
 	unsigned long pfn;
 	struct page *page, *head;
@@ -1721,8 +1720,6 @@ do_migrate_range(unsigned long start_pfn, unsigned long end_pfn)
 			putback_movable_pages(&source);
 		}
 	}
-
-	return ret;
 }
 
 static int __init cmdline_parse_movable_node(char *p)
-- 
2.25.1

[PATCH v2 2/2] mm/memory_hotplug: cleanup 'ret' variable usage in do_migrate_range()

[SeongJae Park]

Because do_migrate_range() is returning nothing, some 'ret' variable
usages are unnecessary.  Remove unnecessary usage and reduce its scope.

Signed-off-by: SeongJae Park <sj@kernel.org>
---
 mm/memory_hotplug.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
index 6c615ba1a5c7..6df3072d11df 100644
--- a/mm/memory_hotplug.c
+++ b/mm/memory_hotplug.c
@@ -1624,7 +1624,6 @@ static void do_migrate_range(unsigned long start_pfn, unsigned long end_pfn)
 {
 	unsigned long pfn;
 	struct page *page, *head;
-	int ret = 0;
 	LIST_HEAD(source);
 	static DEFINE_RATELIMIT_STATE(migrate_rs, DEFAULT_RATELIMIT_INTERVAL,
 				      DEFAULT_RATELIMIT_BURST);
@@ -1678,7 +1677,6 @@ static void do_migrate_range(unsigned long start_pfn, unsigned long end_pfn)
 						    page_is_file_lru(page));
 
 		} else {
-			ret = -EBUSY;
 			if (__ratelimit(&migrate_rs)) {
 				pr_warn("failed to isolate pfn %lx\n", pfn);
 				dump_page(page, "isolation failed");
@@ -1692,6 +1690,7 @@ static void do_migrate_range(unsigned long start_pfn, unsigned long end_pfn)
 			.nmask = &nmask,
 			.gfp_mask = GFP_USER | __GFP_MOVABLE | __GFP_RETRY_MAYFAIL,
 		};
+		int ret;
 
 		/*
 		 * We have checked that migration range is on a single zone so
-- 
2.25.1

Re: [PATCH v2 1/2] mm/memory_hotplug: return nothing from do_migrate_range()

[David Hildenbrand]

On 16.02.23 00:02, SeongJae Park wrote:
> Return value mechanism of do_migrate_range() is not very simple, while
> no caller of the function checks the return value.  Make the function
> return nothing to be more simple.
> 
> Suggested-by: David Hildenbrand <david@redhat.com>
> Signed-off-by: SeongJae Park <sj@kernel.org>
> ---
>   mm/memory_hotplug.c | 5 +----
>   1 file changed, 1 insertion(+), 4 deletions(-)
> 
> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
> index bcb0dc41c2f2..6c615ba1a5c7 100644
> --- a/mm/memory_hotplug.c
> +++ b/mm/memory_hotplug.c
> @@ -1620,8 +1620,7 @@ static int scan_movable_pages(unsigned long start, unsigned long end,
>   	return 0;
>   }
>   
> -static int
> -do_migrate_range(unsigned long start_pfn, unsigned long end_pfn)
> +static void do_migrate_range(unsigned long start_pfn, unsigned long end_pfn)
>   {
>   	unsigned long pfn;
>   	struct page *page, *head;
> @@ -1721,8 +1720,6 @@ do_migrate_range(unsigned long start_pfn, unsigned long end_pfn)
>   			putback_movable_pages(&source);
>   		}
>   	}
> -
> -	return ret;
>   }

I think this patch should also stop initializing ret = 0 inside that 
function.

With that

Acked-by: David Hildenbrand <david@redhat.com>

-- 
Thanks,

David / dhildenb

Re: [PATCH v2 2/2] mm/memory_hotplug: cleanup 'ret' variable usage in do_migrate_range()

[David Hildenbrand]

On 16.02.23 00:03, SeongJae Park wrote:
> Because do_migrate_range() is returning nothing, some 'ret' variable
> usages are unnecessary.  Remove unnecessary usage and reduce its scope.
> 
> Signed-off-by: SeongJae Park <sj@kernel.org>
> ---
>   mm/memory_hotplug.c | 3 +--
>   1 file changed, 1 insertion(+), 2 deletions(-)
> 
> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
> index 6c615ba1a5c7..6df3072d11df 100644
> --- a/mm/memory_hotplug.c
> +++ b/mm/memory_hotplug.c
> @@ -1624,7 +1624,6 @@ static void do_migrate_range(unsigned long start_pfn, unsigned long end_pfn)
>   {
>   	unsigned long pfn;
>   	struct page *page, *head;
> -	int ret = 0;
>   	LIST_HEAD(source);
>   	static DEFINE_RATELIMIT_STATE(migrate_rs, DEFAULT_RATELIMIT_INTERVAL,
>   				      DEFAULT_RATELIMIT_BURST);
> @@ -1678,7 +1677,6 @@ static void do_migrate_range(unsigned long start_pfn, unsigned long end_pfn)
>   						    page_is_file_lru(page));
>   
>   		} else {
> -			ret = -EBUSY;
>   			if (__ratelimit(&migrate_rs)) {
>   				pr_warn("failed to isolate pfn %lx\n", pfn);
>   				dump_page(page, "isolation failed");
> @@ -1692,6 +1690,7 @@ static void do_migrate_range(unsigned long start_pfn, unsigned long end_pfn)
>   			.nmask = &nmask,
>   			.gfp_mask = GFP_USER | __GFP_MOVABLE | __GFP_RETRY_MAYFAIL,
>   		};
> +		int ret;
>   
>   		/*
>   		 * We have checked that migration range is on a single zone so

Please squash that into the previous patch, just calling it 
"mm/memory_hotplug: cleanup return value handling in do_migrate_range()" 
or similar.

-- 
Thanks,

David / dhildenb

Re: [PATCH v2 1/2] mm/memory_hotplug: return nothing from do_migrate_range()

[Baolin Wang]

On 2/16/2023 7:02 AM, SeongJae Park wrote:
> Return value mechanism of do_migrate_range() is not very simple, while
> no caller of the function checks the return value.  Make the function
> return nothing to be more simple.
> 
> Suggested-by: David Hildenbrand <david@redhat.com>
> Signed-off-by: SeongJae Park <sj@kernel.org>
> ---
>   mm/memory_hotplug.c | 5 +----
>   1 file changed, 1 insertion(+), 4 deletions(-)
> 
> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
> index bcb0dc41c2f2..6c615ba1a5c7 100644
> --- a/mm/memory_hotplug.c
> +++ b/mm/memory_hotplug.c
> @@ -1620,8 +1620,7 @@ static int scan_movable_pages(unsigned long start, unsigned long end,
>   	return 0;
>   }
>   
> -static int
> -do_migrate_range(unsigned long start_pfn, unsigned long end_pfn)
> +static void do_migrate_range(unsigned long start_pfn, unsigned long end_pfn)
>   {
>   	unsigned long pfn;
>   	struct page *page, *head;
> @@ -1721,8 +1720,6 @@ do_migrate_range(unsigned long start_pfn, unsigned long end_pfn)
>   			putback_movable_pages(&source);
>   		}
>   	}
> -
> -	return ret;

Nit: while we are at it, can we also remove the "TODO" comment in 
offline_pages()?

ret = scan_movable_pages(pfn, end_pfn, &pfn);
if (!ret) {
	/*
	 * TODO: fatal migration failures should bail
	 * out
	 */
	do_migrate_range(pfn, end_pfn);
}

With David's comments:
Reviewed-by: Baolin Wang <baolin.wang@linux.alibaba.com>

Re: [PATCH v2 1/2] mm/memory_hotplug: return nothing from do_migrate_range()

[SeongJae Park]

Hi David,

On Thu, 16 Feb 2023 10:46:59 +0100 David Hildenbrand <david@redhat.com> wrote:

> On 16.02.23 00:02, SeongJae Park wrote:
> > Return value mechanism of do_migrate_range() is not very simple, while
> > no caller of the function checks the return value.  Make the function
> > return nothing to be more simple.
> > 
> > Suggested-by: David Hildenbrand <david@redhat.com>
> > Signed-off-by: SeongJae Park <sj@kernel.org>
> > ---
> >   mm/memory_hotplug.c | 5 +----
> >   1 file changed, 1 insertion(+), 4 deletions(-)
> > 
> > diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
> > index bcb0dc41c2f2..6c615ba1a5c7 100644
> > --- a/mm/memory_hotplug.c
> > +++ b/mm/memory_hotplug.c
> > @@ -1620,8 +1620,7 @@ static int scan_movable_pages(unsigned long start, unsigned long end,
> >   	return 0;
> >   }
> >   
> > -static int
> > -do_migrate_range(unsigned long start_pfn, unsigned long end_pfn)
> > +static void do_migrate_range(unsigned long start_pfn, unsigned long end_pfn)
> >   {
> >   	unsigned long pfn;
> >   	struct page *page, *head;
> > @@ -1721,8 +1720,6 @@ do_migrate_range(unsigned long start_pfn, unsigned long end_pfn)
> >   			putback_movable_pages(&source);
> >   		}
> >   	}
> > -
> > -	return ret;
> >   }
> 
> I think this patch should also stop initializing ret = 0 inside that 
> function.

The second patch does it, and I read your reply to the patch asking squashing
it in this one.  I will send the new version soon.

> 
> With that
> 
> Acked-by: David Hildenbrand <david@redhat.com>

Thanks you.


Thanks,
SJ

> 
> -- 
> Thanks,
> 
> David / dhildenb
> 
> 

Re: [PATCH v2 1/2] mm/memory_hotplug: return nothing from do_migrate_range()

[SeongJae Park]

Hi Baolin,

On Thu, 16 Feb 2023 18:53:34 +0800 Baolin Wang <baolin.wang@linux.alibaba.com> wrote:

> 
> 
> On 2/16/2023 7:02 AM, SeongJae Park wrote:
> > Return value mechanism of do_migrate_range() is not very simple, while
> > no caller of the function checks the return value.  Make the function
> > return nothing to be more simple.
> > 
> > Suggested-by: David Hildenbrand <david@redhat.com>
> > Signed-off-by: SeongJae Park <sj@kernel.org>
> > ---
> >   mm/memory_hotplug.c | 5 +----
> >   1 file changed, 1 insertion(+), 4 deletions(-)
> > 
> > diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
> > index bcb0dc41c2f2..6c615ba1a5c7 100644
> > --- a/mm/memory_hotplug.c
> > +++ b/mm/memory_hotplug.c
> > @@ -1620,8 +1620,7 @@ static int scan_movable_pages(unsigned long start, unsigned long end,
> >   	return 0;
> >   }
> >   
> > -static int
> > -do_migrate_range(unsigned long start_pfn, unsigned long end_pfn)
> > +static void do_migrate_range(unsigned long start_pfn, unsigned long end_pfn)
> >   {
> >   	unsigned long pfn;
> >   	struct page *page, *head;
> > @@ -1721,8 +1720,6 @@ do_migrate_range(unsigned long start_pfn, unsigned long end_pfn)
> >   			putback_movable_pages(&source);
> >   		}
> >   	}
> > -
> > -	return ret;
> 
> Nit: while we are at it, can we also remove the "TODO" comment in 
> offline_pages()?
> 
> ret = scan_movable_pages(pfn, end_pfn, &pfn);
> if (!ret) {
> 	/*
> 	 * TODO: fatal migration failures should bail
> 	 * out
> 	 */
> 	do_migrate_range(pfn, end_pfn);
> }
> 
> With David's comments:
> Reviewed-by: Baolin Wang <baolin.wang@linux.alibaba.com>

As David mentioned we're just still unclear what issues are fatal[1], I was
thinking we didn't forgive the future work, so left the comment.  If anyone has
different opinion or I'm getting something wrong, please let me know.

[1] https://lore.kernel.org/linux-mm/388b9a93-423f-33f8-0495-2a4a290fd1aa@redhat.com/


Thanks,
SJ