diff mbox series

[v9,2/8] mm,memory_hotplug: Relax fully spanned sections check

Message ID 20210416112411.9826-3-osalvador@suse.de (mailing list archive)
State New
Headers show
Series [v9,1/8] drivers/base/memory: Introduce memory_block_{online,offline} | expand

Commit Message

Oscar Salvador April 16, 2021, 11:24 a.m. UTC
When using self-hosted vmemmap pages, the number of pages passed to
{online,offline}_pages might not fully span sections, but they always
fully span pageblocks.
Relax the check account for that case.

Signed-off-by: Oscar Salvador <osalvador@suse.de>
Reviewed-by: David Hildenbrand <david@redhat.com>
---
 mm/memory_hotplug.c | 18 ++++++++++++++----
 1 file changed, 14 insertions(+), 4 deletions(-)

Comments

Michal Hocko April 20, 2021, 9:40 a.m. UTC | #1
On Fri 16-04-21 13:24:05, Oscar Salvador wrote:
> When using self-hosted vmemmap pages, the number of pages passed to
> {online,offline}_pages might not fully span sections, but they always
> fully span pageblocks.
> Relax the check account for that case.

It would be good to call those out explicitly.  It would be also
great to explain why pageblock_nr_pages is an actual constrain. There
shouldn't be any real reason for that except for "we want online_pages
to operate on whole memblocks and memmap_on_memory will poke
pageblock_nr_pages aligned holes in the beginning which is a special
case we want to allow."

> Signed-off-by: Oscar Salvador <osalvador@suse.de>
> Reviewed-by: David Hildenbrand <david@redhat.com>

With the changelog extended and the comment clarification (se below)
feel free to add
Acked-by: Michal Hocko <mhocko@suse.com>

> ---
>  mm/memory_hotplug.c | 18 ++++++++++++++----
>  1 file changed, 14 insertions(+), 4 deletions(-)
> 
> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
> index 0cdbbfbc5757..25e59d5dc13c 100644
> --- a/mm/memory_hotplug.c
> +++ b/mm/memory_hotplug.c
> @@ -838,9 +838,14 @@ int __ref online_pages(unsigned long pfn, unsigned long nr_pages,
>  	int ret;
>  	struct memory_notify arg;
>  
> -	/* We can only online full sections (e.g., SECTION_IS_ONLINE) */
> +	/* We can only offline full sections (e.g., SECTION_IS_ONLINE).
> +	 * However, when using e.g: memmap_on_memory, some pages are initialized
> +	 * prior to calling in here. The remaining amount of pages must be
> +	 * pageblock aligned.


I would rephrase (and also note that multi line comment usually have a
leading line without any content - not that I care much though).

	/*
	 * {on,off}lining is constrained to full memory sections (or
	 * more precisly to memory blocks from the user space POV).
	 * memmap_on_memory is an exception because it reserves initial
	 * part of the physical memory space for vmemmaps. That space is
	 * pageblock aligned.
> +	 */

Same comment would apply to oofline_pages.

>  	if (WARN_ON_ONCE(!nr_pages ||
> -			 !IS_ALIGNED(pfn | nr_pages, PAGES_PER_SECTION)))
> +			 !IS_ALIGNED(pfn, pageblock_nr_pages) ||
> +			 !IS_ALIGNED(pfn + nr_pages, PAGES_PER_SECTION)))
>  		return -EINVAL;
>  
>  	mem_hotplug_begin();
> @@ -1573,9 +1578,14 @@ int __ref offline_pages(unsigned long start_pfn, unsigned long nr_pages)
>  	int ret, node;
>  	char *reason;
>  
> -	/* We can only offline full sections (e.g., SECTION_IS_ONLINE) */
> +	/* We can only offline full sections (e.g., SECTION_IS_ONLINE).
> +	 * However, when using e.g: memmap_on_memory, some pages are initialized
> +	 * prior to calling in here. The remaining amount of pages must be
> +	 * pageblock aligned.
> +	 */
>  	if (WARN_ON_ONCE(!nr_pages ||
> -			 !IS_ALIGNED(start_pfn | nr_pages, PAGES_PER_SECTION)))
> +			 !IS_ALIGNED(start_pfn, pageblock_nr_pages) ||
> +			 !IS_ALIGNED(start_pfn + nr_pages, PAGES_PER_SECTION)))
>  		return -EINVAL;
>  
>  	mem_hotplug_begin();
> -- 
> 2.16.3
Oscar Salvador April 21, 2021, 7:37 a.m. UTC | #2
On Tue, Apr 20, 2021 at 11:40:50AM +0200, Michal Hocko wrote:
> On Fri 16-04-21 13:24:05, Oscar Salvador wrote:
> > When using self-hosted vmemmap pages, the number of pages passed to
> > {online,offline}_pages might not fully span sections, but they always
> > fully span pageblocks.
> > Relax the check account for that case.
> 
> It would be good to call those out explicitly.  It would be also
> great to explain why pageblock_nr_pages is an actual constrain. There
> shouldn't be any real reason for that except for "we want online_pages
> to operate on whole memblocks and memmap_on_memory will poke
> pageblock_nr_pages aligned holes in the beginning which is a special
> case we want to allow."

Sounds good.

> 
> > Signed-off-by: Oscar Salvador <osalvador@suse.de>
> > Reviewed-by: David Hildenbrand <david@redhat.com>
> 
> With the changelog extended and the comment clarification (se below)
> feel free to add

Ok, thanks for the suggestion Michal.

> Acked-by: Michal Hocko <mhocko@suse.com>
diff mbox series

Patch

diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
index 0cdbbfbc5757..25e59d5dc13c 100644
--- a/mm/memory_hotplug.c
+++ b/mm/memory_hotplug.c
@@ -838,9 +838,14 @@  int __ref online_pages(unsigned long pfn, unsigned long nr_pages,
 	int ret;
 	struct memory_notify arg;
 
-	/* We can only online full sections (e.g., SECTION_IS_ONLINE) */
+	/* We can only offline full sections (e.g., SECTION_IS_ONLINE).
+	 * However, when using e.g: memmap_on_memory, some pages are initialized
+	 * prior to calling in here. The remaining amount of pages must be
+	 * pageblock aligned.
+	 */
 	if (WARN_ON_ONCE(!nr_pages ||
-			 !IS_ALIGNED(pfn | nr_pages, PAGES_PER_SECTION)))
+			 !IS_ALIGNED(pfn, pageblock_nr_pages) ||
+			 !IS_ALIGNED(pfn + nr_pages, PAGES_PER_SECTION)))
 		return -EINVAL;
 
 	mem_hotplug_begin();
@@ -1573,9 +1578,14 @@  int __ref offline_pages(unsigned long start_pfn, unsigned long nr_pages)
 	int ret, node;
 	char *reason;
 
-	/* We can only offline full sections (e.g., SECTION_IS_ONLINE) */
+	/* We can only offline full sections (e.g., SECTION_IS_ONLINE).
+	 * However, when using e.g: memmap_on_memory, some pages are initialized
+	 * prior to calling in here. The remaining amount of pages must be
+	 * pageblock aligned.
+	 */
 	if (WARN_ON_ONCE(!nr_pages ||
-			 !IS_ALIGNED(start_pfn | nr_pages, PAGES_PER_SECTION)))
+			 !IS_ALIGNED(start_pfn, pageblock_nr_pages) ||
+			 !IS_ALIGNED(start_pfn + nr_pages, PAGES_PER_SECTION)))
 		return -EINVAL;
 
 	mem_hotplug_begin();