[PATCH v2 0/5] mm/memory_hotplug: online_pages() cleanups

[PATCH v2 0/5] mm/memory_hotplug: online_pages() cleanups

[David Hildenbrand]

Some cleanups (+ one fix for a special case) in the context of
online_pages(). Hope I am not missing something obvious. Did a sanity test
with DIMMs only.

v1 -> v2:
- "mm/memory_hotplug: Handle unaligned start and nr_pages in
   online_pages_blocks()"
-- Turned into "mm/memory_hotplug: make sure the pfn is aligned to the
		order when onlining"
-- Dropped the "nr_pages not an order of two" condition for now as
   requested by Michal, but kept a simplified alignment check
- "mm/memory_hotplug: Drop PageReserved() check in online_pages_range()"
-- Split out from "mm/memory_hotplug: Simplify online_pages_range()"
- "mm/memory_hotplug: Simplify online_pages_range()"
-- Modified due to the other changes

David Hildenbrand (5):
  resource: Use PFN_UP / PFN_DOWN in walk_system_ram_range()
  mm/memory_hotplug: Drop PageReserved() check in online_pages_range()
  mm/memory_hotplug: Simplify online_pages_range()
  mm/memory_hotplug: Make sure the pfn is aligned to the order when
    onlining
  mm/memory_hotplug: online_pages cannot be 0 in online_pages()

 kernel/resource.c   |  4 +--
 mm/memory_hotplug.c | 61 ++++++++++++++++++++-------------------------
 2 files changed, 29 insertions(+), 36 deletions(-)

-- 
2.21.0

[PATCH v2 1/5] resource: Use PFN_UP / PFN_DOWN in walk_system_ram_range()

[David Hildenbrand]

This makes it clearer that we will never call func() with duplicate PFNs
in case we have multiple sub-page memory resources. All unaligned parts
of PFNs are completely discarded.

Cc: Dan Williams <dan.j.williams@intel.com>
Cc: Borislav Petkov <bp@suse.de>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Bjorn Helgaas <bhelgaas@google.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Nadav Amit <namit@vmware.com>
Cc: Wei Yang <richardw.yang@linux.intel.com>
Cc: Oscar Salvador <osalvador@suse.de>
Acked-by: Michal Hocko <mhocko@suse.com>
Signed-off-by: David Hildenbrand <david@redhat.com>
---
 kernel/resource.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/kernel/resource.c b/kernel/resource.c
index 7ea4306503c5..88ee39fa9103 100644
--- a/kernel/resource.c
+++ b/kernel/resource.c
@@ -487,8 +487,8 @@ int walk_system_ram_range(unsigned long start_pfn, unsigned long nr_pages,
 	while (start < end &&
 	       !find_next_iomem_res(start, end, flags, IORES_DESC_NONE,
 				    false, &res)) {
-		pfn = (res.start + PAGE_SIZE - 1) >> PAGE_SHIFT;
-		end_pfn = (res.end + 1) >> PAGE_SHIFT;
+		pfn = PFN_UP(res.start);
+		end_pfn = PFN_DOWN(res.end + 1);
 		if (end_pfn > pfn)
 			ret = (*func)(pfn, end_pfn - pfn, arg);
 		if (ret)
-- 
2.21.0

Re: [PATCH v2 1/5] resource: Use PFN_UP / PFN_DOWN in walk_system_ram_range()

[Wei Yang]

On Wed, Aug 14, 2019 at 05:41:05PM +0200, David Hildenbrand wrote:
>This makes it clearer that we will never call func() with duplicate PFNs
>in case we have multiple sub-page memory resources. All unaligned parts
>of PFNs are completely discarded.
>
>Cc: Dan Williams <dan.j.williams@intel.com>
>Cc: Borislav Petkov <bp@suse.de>
>Cc: Andrew Morton <akpm@linux-foundation.org>
>Cc: Bjorn Helgaas <bhelgaas@google.com>
>Cc: Ingo Molnar <mingo@kernel.org>
>Cc: Dave Hansen <dave.hansen@linux.intel.com>
>Cc: Nadav Amit <namit@vmware.com>
>Cc: Wei Yang <richardw.yang@linux.intel.com>
>Cc: Oscar Salvador <osalvador@suse.de>
>Acked-by: Michal Hocko <mhocko@suse.com>
>Signed-off-by: David Hildenbrand <david@redhat.com>

Reviewed-by: Wei Yang <richardw.yang@linux.intel.com>

>---
> kernel/resource.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
>diff --git a/kernel/resource.c b/kernel/resource.c
>index 7ea4306503c5..88ee39fa9103 100644
>--- a/kernel/resource.c
>+++ b/kernel/resource.c
>@@ -487,8 +487,8 @@ int walk_system_ram_range(unsigned long start_pfn, unsigned long nr_pages,
> 	while (start < end &&
> 	       !find_next_iomem_res(start, end, flags, IORES_DESC_NONE,
> 				    false, &res)) {
>-		pfn = (res.start + PAGE_SIZE - 1) >> PAGE_SHIFT;
>-		end_pfn = (res.end + 1) >> PAGE_SHIFT;
>+		pfn = PFN_UP(res.start);
>+		end_pfn = PFN_DOWN(res.end + 1);
> 		if (end_pfn > pfn)
> 			ret = (*func)(pfn, end_pfn - pfn, arg);
> 		if (ret)
>-- 
>2.21.0

-- 
Wei Yang
Help you, Help me

[PATCH v2 2/5] mm/memory_hotplug: Drop PageReserved() check in online_pages_range()

[David Hildenbrand]

move_pfn_range_to_zone() will set all pages to PG_reserved via
memmap_init_zone(). The only way a page could no longer be reserved
would be if a MEM_GOING_ONLINE notifier would clear PG_reserved - which
is not done (the online_page callback is used for that purpose by
e.g., Hyper-V instead). walk_system_ram_range() will never call
online_pages_range() with duplicate PFNs, so drop the PageReserved() check.

This seems to be a leftover from ancient times where the memmap was
initialized when adding memory and we wanted to check for already
onlined memory.

Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Pavel Tatashin <pasha.tatashin@soleen.com>
Cc: Dan Williams <dan.j.williams@intel.com>
Signed-off-by: David Hildenbrand <david@redhat.com>
---
 mm/memory_hotplug.c | 4 +---
 1 file changed, 1 insertion(+), 3 deletions(-)

diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
index 3706a137d880..10ad970f3f14 100644
--- a/mm/memory_hotplug.c
+++ b/mm/memory_hotplug.c
@@ -653,9 +653,7 @@ static int online_pages_range(unsigned long start_pfn, unsigned long nr_pages,
 {
 	unsigned long onlined_pages = *(unsigned long *)arg;
 
-	if (PageReserved(pfn_to_page(start_pfn)))
-		onlined_pages += online_pages_blocks(start_pfn, nr_pages);
-
+	onlined_pages += online_pages_blocks(start_pfn, nr_pages);
 	online_mem_sections(start_pfn, start_pfn + nr_pages);
 
 	*(unsigned long *)arg = onlined_pages;
-- 
2.21.0

Re: [PATCH v2 2/5] mm/memory_hotplug: Drop PageReserved() check in online_pages_range()

[Michal Hocko]

On Wed 14-08-19 17:41:06, David Hildenbrand wrote:
> move_pfn_range_to_zone() will set all pages to PG_reserved via
> memmap_init_zone(). The only way a page could no longer be reserved
> would be if a MEM_GOING_ONLINE notifier would clear PG_reserved - which
> is not done (the online_page callback is used for that purpose by
> e.g., Hyper-V instead). walk_system_ram_range() will never call
> online_pages_range() with duplicate PFNs, so drop the PageReserved() check.
> 
> This seems to be a leftover from ancient times where the memmap was
> initialized when adding memory and we wanted to check for already
> onlined memory.
> 
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Cc: Oscar Salvador <osalvador@suse.de>
> Cc: Michal Hocko <mhocko@suse.com>
> Cc: Pavel Tatashin <pasha.tatashin@soleen.com>
> Cc: Dan Williams <dan.j.williams@intel.com>
> Signed-off-by: David Hildenbrand <david@redhat.com>

Thanks for spliting that up.
Acked-by: Michal Hocko <mhocko@suse.com>

> ---
>  mm/memory_hotplug.c | 4 +---
>  1 file changed, 1 insertion(+), 3 deletions(-)
> 
> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
> index 3706a137d880..10ad970f3f14 100644
> --- a/mm/memory_hotplug.c
> +++ b/mm/memory_hotplug.c
> @@ -653,9 +653,7 @@ static int online_pages_range(unsigned long start_pfn, unsigned long nr_pages,
>  {
>  	unsigned long onlined_pages = *(unsigned long *)arg;
>  
> -	if (PageReserved(pfn_to_page(start_pfn)))
> -		onlined_pages += online_pages_blocks(start_pfn, nr_pages);
> -
> +	onlined_pages += online_pages_blocks(start_pfn, nr_pages);
>  	online_mem_sections(start_pfn, start_pfn + nr_pages);
>  
>  	*(unsigned long *)arg = onlined_pages;
> -- 
> 2.21.0
> 

-- 
Michal Hocko
SUSE Labs

[PATCH v2 3/5] mm/memory_hotplug: Simplify online_pages_range()

[David Hildenbrand]

online_pages always corresponds to nr_pages. Simplify the code, getting
rid of online_pages_blocks(). Add some comments.

Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Pavel Tatashin <pasha.tatashin@soleen.com>
Cc: Dan Williams <dan.j.williams@intel.com>
Signed-off-by: David Hildenbrand <david@redhat.com>
---
 mm/memory_hotplug.c | 36 ++++++++++++++++--------------------
 1 file changed, 16 insertions(+), 20 deletions(-)

diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
index 10ad970f3f14..63b1775f7cf8 100644
--- a/mm/memory_hotplug.c
+++ b/mm/memory_hotplug.c
@@ -632,31 +632,27 @@ static void generic_online_page(struct page *page, unsigned int order)
 #endif
 }
 
-static int online_pages_blocks(unsigned long start, unsigned long nr_pages)
-{
-	unsigned long end = start + nr_pages;
-	int order, onlined_pages = 0;
-
-	while (start < end) {
-		order = min(MAX_ORDER - 1,
-			get_order(PFN_PHYS(end) - PFN_PHYS(start)));
-		(*online_page_callback)(pfn_to_page(start), order);
-
-		onlined_pages += (1UL << order);
-		start += (1UL << order);
-	}
-	return onlined_pages;
-}
-
 static int online_pages_range(unsigned long start_pfn, unsigned long nr_pages,
 			void *arg)
 {
-	unsigned long onlined_pages = *(unsigned long *)arg;
+	const unsigned long end_pfn = start_pfn + nr_pages;
+	unsigned long pfn;
+	int order;
+
+	/*
+	 * Online the pages. The callback might decide to keep some pages
+	 * PG_reserved (to add them to the buddy later), but we still account
+	 * them as being online/belonging to this zone ("present").
+	 */
+	for (pfn = start_pfn; pfn < end_pfn; pfn += 1ul << order) {
+		order = min(MAX_ORDER - 1, get_order(PFN_PHYS(end_pfn - pfn)));
+		(*online_page_callback)(pfn_to_page(pfn), order);
+	}
 
-	onlined_pages += online_pages_blocks(start_pfn, nr_pages);
-	online_mem_sections(start_pfn, start_pfn + nr_pages);
+	/* mark all involved sections as online */
+	online_mem_sections(start_pfn, end_pfn);
 
-	*(unsigned long *)arg = onlined_pages;
+	*(unsigned long *)arg += nr_pages;
 	return 0;
 }
 
-- 
2.21.0

Re: [PATCH v2 3/5] mm/memory_hotplug: Simplify online_pages_range()

[Michal Hocko]

On Wed 14-08-19 17:41:07, David Hildenbrand wrote:
> online_pages always corresponds to nr_pages. Simplify the code, getting
> rid of online_pages_blocks(). Add some comments.
> 
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Cc: Oscar Salvador <osalvador@suse.de>
> Cc: Michal Hocko <mhocko@suse.com>
> Cc: Pavel Tatashin <pasha.tatashin@soleen.com>
> Cc: Dan Williams <dan.j.williams@intel.com>
> Signed-off-by: David Hildenbrand <david@redhat.com>

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

Thanks!

> ---
>  mm/memory_hotplug.c | 36 ++++++++++++++++--------------------
>  1 file changed, 16 insertions(+), 20 deletions(-)
> 
> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
> index 10ad970f3f14..63b1775f7cf8 100644
> --- a/mm/memory_hotplug.c
> +++ b/mm/memory_hotplug.c
> @@ -632,31 +632,27 @@ static void generic_online_page(struct page *page, unsigned int order)
>  #endif
>  }
>  
> -static int online_pages_blocks(unsigned long start, unsigned long nr_pages)
> -{
> -	unsigned long end = start + nr_pages;
> -	int order, onlined_pages = 0;
> -
> -	while (start < end) {
> -		order = min(MAX_ORDER - 1,
> -			get_order(PFN_PHYS(end) - PFN_PHYS(start)));
> -		(*online_page_callback)(pfn_to_page(start), order);
> -
> -		onlined_pages += (1UL << order);
> -		start += (1UL << order);
> -	}
> -	return onlined_pages;
> -}
> -
>  static int online_pages_range(unsigned long start_pfn, unsigned long nr_pages,
>  			void *arg)
>  {
> -	unsigned long onlined_pages = *(unsigned long *)arg;
> +	const unsigned long end_pfn = start_pfn + nr_pages;
> +	unsigned long pfn;
> +	int order;
> +
> +	/*
> +	 * Online the pages. The callback might decide to keep some pages
> +	 * PG_reserved (to add them to the buddy later), but we still account
> +	 * them as being online/belonging to this zone ("present").
> +	 */
> +	for (pfn = start_pfn; pfn < end_pfn; pfn += 1ul << order) {
> +		order = min(MAX_ORDER - 1, get_order(PFN_PHYS(end_pfn - pfn)));
> +		(*online_page_callback)(pfn_to_page(pfn), order);
> +	}
>  
> -	onlined_pages += online_pages_blocks(start_pfn, nr_pages);
> -	online_mem_sections(start_pfn, start_pfn + nr_pages);
> +	/* mark all involved sections as online */
> +	online_mem_sections(start_pfn, end_pfn);
>  
> -	*(unsigned long *)arg = onlined_pages;
> +	*(unsigned long *)arg += nr_pages;
>  	return 0;
>  }
>  
> -- 
> 2.21.0
> 

-- 
Michal Hocko
SUSE Labs

[PATCH v2 4/5] mm/memory_hotplug: Make sure the pfn is aligned to the order when onlining

[David Hildenbrand]

Commit a9cd410a3d29 ("mm/page_alloc.c: memory hotplug: free pages as higher
order") assumed that any PFN we get via memory resources is aligned to
to MAX_ORDER - 1, I am not convinced that is always true. Let's play safe,
check the alignment and fallback to single pages.

Cc: Arun KS <arunks@codeaurora.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Pavel Tatashin <pasha.tatashin@soleen.com>
Cc: Dan Williams <dan.j.williams@intel.com>
Signed-off-by: David Hildenbrand <david@redhat.com>
---
 mm/memory_hotplug.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
index 63b1775f7cf8..f245fb50ba7f 100644
--- a/mm/memory_hotplug.c
+++ b/mm/memory_hotplug.c
@@ -646,6 +646,9 @@ static int online_pages_range(unsigned long start_pfn, unsigned long nr_pages,
 	 */
 	for (pfn = start_pfn; pfn < end_pfn; pfn += 1ul << order) {
 		order = min(MAX_ORDER - 1, get_order(PFN_PHYS(end_pfn - pfn)));
+		/* __free_pages_core() wants pfns to be aligned to the order */
+		if (unlikely(!IS_ALIGNED(pfn, 1ul << order)))
+			order = 0;
 		(*online_page_callback)(pfn_to_page(pfn), order);
 	}
 
-- 
2.21.0

Re: [PATCH v2 4/5] mm/memory_hotplug: Make sure the pfn is aligned to the order when onlining

[David Hildenbrand]

On 14.08.19 17:41, David Hildenbrand wrote:
> Commit a9cd410a3d29 ("mm/page_alloc.c: memory hotplug: free pages as higher
> order") assumed that any PFN we get via memory resources is aligned to
> to MAX_ORDER - 1, I am not convinced that is always true. Let's play safe,
> check the alignment and fallback to single pages.
> 
> Cc: Arun KS <arunks@codeaurora.org>
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Cc: Oscar Salvador <osalvador@suse.de>
> Cc: Michal Hocko <mhocko@suse.com>
> Cc: Pavel Tatashin <pasha.tatashin@soleen.com>
> Cc: Dan Williams <dan.j.williams@intel.com>
> Signed-off-by: David Hildenbrand <david@redhat.com>
> ---
>  mm/memory_hotplug.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
> index 63b1775f7cf8..f245fb50ba7f 100644
> --- a/mm/memory_hotplug.c
> +++ b/mm/memory_hotplug.c
> @@ -646,6 +646,9 @@ static int online_pages_range(unsigned long start_pfn, unsigned long nr_pages,
>  	 */
>  	for (pfn = start_pfn; pfn < end_pfn; pfn += 1ul << order) {
>  		order = min(MAX_ORDER - 1, get_order(PFN_PHYS(end_pfn - pfn)));
> +		/* __free_pages_core() wants pfns to be aligned to the order */
> +		if (unlikely(!IS_ALIGNED(pfn, 1ul << order)))
> +			order = 0;
>  		(*online_page_callback)(pfn_to_page(pfn), order);
>  	}
>  
> 

@Michal, if you insist, we can drop this patch. "break first and fix
later" is not part of my DNA :)

-- 

Thanks,

David / dhildenb

Re: [PATCH v2 4/5] mm/memory_hotplug: Make sure the pfn is aligned to the order when onlining

[Michal Hocko]

On Wed 14-08-19 18:09:16, David Hildenbrand wrote:
> On 14.08.19 17:41, David Hildenbrand wrote:
> > Commit a9cd410a3d29 ("mm/page_alloc.c: memory hotplug: free pages as higher
> > order") assumed that any PFN we get via memory resources is aligned to
> > to MAX_ORDER - 1, I am not convinced that is always true. Let's play safe,
> > check the alignment and fallback to single pages.
> > 
> > Cc: Arun KS <arunks@codeaurora.org>
> > Cc: Andrew Morton <akpm@linux-foundation.org>
> > Cc: Oscar Salvador <osalvador@suse.de>
> > Cc: Michal Hocko <mhocko@suse.com>
> > Cc: Pavel Tatashin <pasha.tatashin@soleen.com>
> > Cc: Dan Williams <dan.j.williams@intel.com>
> > Signed-off-by: David Hildenbrand <david@redhat.com>
> > ---
> >  mm/memory_hotplug.c | 3 +++
> >  1 file changed, 3 insertions(+)
> > 
> > diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
> > index 63b1775f7cf8..f245fb50ba7f 100644
> > --- a/mm/memory_hotplug.c
> > +++ b/mm/memory_hotplug.c
> > @@ -646,6 +646,9 @@ static int online_pages_range(unsigned long start_pfn, unsigned long nr_pages,
> >  	 */
> >  	for (pfn = start_pfn; pfn < end_pfn; pfn += 1ul << order) {
> >  		order = min(MAX_ORDER - 1, get_order(PFN_PHYS(end_pfn - pfn)));
> > +		/* __free_pages_core() wants pfns to be aligned to the order */
> > +		if (unlikely(!IS_ALIGNED(pfn, 1ul << order)))
> > +			order = 0;
> >  		(*online_page_callback)(pfn_to_page(pfn), order);
> >  	}
> >  
> > 
> 
> @Michal, if you insist, we can drop this patch. "break first and fix
> later" is not part of my DNA :)

I do not insist but have already expressed that I am not a fan of this
change. Also I think that "break first" is quite an over statement here.

-- 
Michal Hocko
SUSE Labs

Re: [PATCH v2 4/5] mm/memory_hotplug: Make sure the pfn is aligned to the order when onlining

[David Hildenbrand]

On 14.08.19 20:32, Michal Hocko wrote:
> On Wed 14-08-19 18:09:16, David Hildenbrand wrote:
>> On 14.08.19 17:41, David Hildenbrand wrote:
>>> Commit a9cd410a3d29 ("mm/page_alloc.c: memory hotplug: free pages as higher
>>> order") assumed that any PFN we get via memory resources is aligned to
>>> to MAX_ORDER - 1, I am not convinced that is always true. Let's play safe,
>>> check the alignment and fallback to single pages.
>>>
>>> Cc: Arun KS <arunks@codeaurora.org>
>>> Cc: Andrew Morton <akpm@linux-foundation.org>
>>> Cc: Oscar Salvador <osalvador@suse.de>
>>> Cc: Michal Hocko <mhocko@suse.com>
>>> Cc: Pavel Tatashin <pasha.tatashin@soleen.com>
>>> Cc: Dan Williams <dan.j.williams@intel.com>
>>> Signed-off-by: David Hildenbrand <david@redhat.com>
>>> ---
>>>  mm/memory_hotplug.c | 3 +++
>>>  1 file changed, 3 insertions(+)
>>>
>>> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
>>> index 63b1775f7cf8..f245fb50ba7f 100644
>>> --- a/mm/memory_hotplug.c
>>> +++ b/mm/memory_hotplug.c
>>> @@ -646,6 +646,9 @@ static int online_pages_range(unsigned long start_pfn, unsigned long nr_pages,
>>>  	 */
>>>  	for (pfn = start_pfn; pfn < end_pfn; pfn += 1ul << order) {
>>>  		order = min(MAX_ORDER - 1, get_order(PFN_PHYS(end_pfn - pfn)));
>>> +		/* __free_pages_core() wants pfns to be aligned to the order */
>>> +		if (unlikely(!IS_ALIGNED(pfn, 1ul << order)))
>>> +			order = 0;
>>>  		(*online_page_callback)(pfn_to_page(pfn), order);
>>>  	}
>>>  
>>>
>>
>> @Michal, if you insist, we can drop this patch. "break first and fix
>> later" is not part of my DNA :)
> 
> I do not insist but have already expressed that I am not a fan of this
> change. Also I think that "break first" is quite an over statement here.
> 

Well this version is certainly nicer than the previous one. I'll let
Andrew decide if he wants to pick it up or drop it from this series.

Thanks!

-- 

Thanks,

David / dhildenb

Re: [PATCH v2 4/5] mm/memory_hotplug: Make sure the pfn is aligned to the order when onlining

[Andrew Morton]

On Wed, 14 Aug 2019 17:41:08 +0200 David Hildenbrand <david@redhat.com> wrote:

> Commit a9cd410a3d29 ("mm/page_alloc.c: memory hotplug: free pages as higher
> order") assumed that any PFN we get via memory resources is aligned to
> to MAX_ORDER - 1, I am not convinced that is always true. Let's play safe,
> check the alignment and fallback to single pages.
> 
> ...
>
> --- a/mm/memory_hotplug.c
> +++ b/mm/memory_hotplug.c
> @@ -646,6 +646,9 @@ static int online_pages_range(unsigned long start_pfn, unsigned long nr_pages,
>  	 */
>  	for (pfn = start_pfn; pfn < end_pfn; pfn += 1ul << order) {
>  		order = min(MAX_ORDER - 1, get_order(PFN_PHYS(end_pfn - pfn)));
> +		/* __free_pages_core() wants pfns to be aligned to the order */
> +		if (unlikely(!IS_ALIGNED(pfn, 1ul << order)))
> +			order = 0;
>  		(*online_page_callback)(pfn_to_page(pfn), order);
>  	}

We aren't sure if this occurs, but if it does, we silently handle it.

It seems a reasonable defensive thing to do, but should we add a
WARN_ON_ONCE() so that we get to find out about it?  If we get such a
report then we can remove the WARN_ON_ONCE() and add an illuminating
comment.

Re: [PATCH v2 4/5] mm/memory_hotplug: Make sure the pfn is aligned to the order when onlining

[David Hildenbrand]

On 14.08.19 22:56, Andrew Morton wrote:
> On Wed, 14 Aug 2019 17:41:08 +0200 David Hildenbrand <david@redhat.com> wrote:
> 
>> Commit a9cd410a3d29 ("mm/page_alloc.c: memory hotplug: free pages as higher
>> order") assumed that any PFN we get via memory resources is aligned to
>> to MAX_ORDER - 1, I am not convinced that is always true. Let's play safe,
>> check the alignment and fallback to single pages.
>>
>> ...
>>
>> --- a/mm/memory_hotplug.c
>> +++ b/mm/memory_hotplug.c
>> @@ -646,6 +646,9 @@ static int online_pages_range(unsigned long start_pfn, unsigned long nr_pages,
>>  	 */
>>  	for (pfn = start_pfn; pfn < end_pfn; pfn += 1ul << order) {
>>  		order = min(MAX_ORDER - 1, get_order(PFN_PHYS(end_pfn - pfn)));
>> +		/* __free_pages_core() wants pfns to be aligned to the order */
>> +		if (unlikely(!IS_ALIGNED(pfn, 1ul << order)))
>> +			order = 0;
>>  		(*online_page_callback)(pfn_to_page(pfn), order);
>>  	}
> 
> We aren't sure if this occurs, but if it does, we silently handle it.
> 
> It seems a reasonable defensive thing to do, but should we add a
> WARN_ON_ONCE() so that we get to find out about it?  If we get such a
> report then we can remove the WARN_ON_ONCE() and add an illuminating
> comment.
> 
> 

Makes sense, do you want to add the WARN_ON_ONCE() or shall I resend?

I was recently thinking about limiting offlining to memory blocks
without holes - then also onlining would only apply to memory blocks
without holes and we could simplify both paths (single zone/node, no
holes) - including this check, we would always have memory block size
alignments. But I am not sure yet if there is a valid use case for
offlining/re-online boot memory with holes.

-- 

Thanks,

David / dhildenb

Re: [PATCH v2 4/5] mm/memory_hotplug: Make sure the pfn is aligned to the order when onlining

[Andrew Morton]

On Wed, 14 Aug 2019 23:47:24 +0200 David Hildenbrand <david@redhat.com> wrote:

> >> --- a/mm/memory_hotplug.c
> >> +++ b/mm/memory_hotplug.c
> >> @@ -646,6 +646,9 @@ static int online_pages_range(unsigned long start_pfn, unsigned long nr_pages,
> >>  	 */
> >>  	for (pfn = start_pfn; pfn < end_pfn; pfn += 1ul << order) {
> >>  		order = min(MAX_ORDER - 1, get_order(PFN_PHYS(end_pfn - pfn)));
> >> +		/* __free_pages_core() wants pfns to be aligned to the order */
> >> +		if (unlikely(!IS_ALIGNED(pfn, 1ul << order)))
> >> +			order = 0;
> >>  		(*online_page_callback)(pfn_to_page(pfn), order);
> >>  	}
> > 
> > We aren't sure if this occurs, but if it does, we silently handle it.
> > 
> > It seems a reasonable defensive thing to do, but should we add a
> > WARN_ON_ONCE() so that we get to find out about it?  If we get such a
> > report then we can remove the WARN_ON_ONCE() and add an illuminating
> > comment.
> > 
> > 
> 
> Makes sense, do you want to add the WARN_ON_ONCE() or shall I resend?

--- a/mm/memory_hotplug.c~mm-memory_hotplug-make-sure-the-pfn-is-aligned-to-the-order-when-onlining-fix
+++ a/mm/memory_hotplug.c
@@ -647,7 +647,7 @@ static int online_pages_range(unsigned l
 	for (pfn = start_pfn; pfn < end_pfn; pfn += 1ul << order) {
 		order = min(MAX_ORDER - 1, get_order(PFN_PHYS(end_pfn - pfn)));
 		/* __free_pages_core() wants pfns to be aligned to the order */
-		if (unlikely(!IS_ALIGNED(pfn, 1ul << order)))
+		if (WARN_ON_ONCE(!IS_ALIGNED(pfn, 1ul << order)))
 			order = 0;
 		(*online_page_callback)(pfn_to_page(pfn), order);
 	}
_

[PATCH v2 5/5] mm/memory_hotplug: online_pages cannot be 0 in online_pages()

[David Hildenbrand]

walk_system_ram_range() will fail with -EINVAL in case
online_pages_range() was never called (== no resource applicable in the
range). Otherwise, we will always call online_pages_range() with
nr_pages > 0 and, therefore, have online_pages > 0.

Remove that special handling.

Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Pavel Tatashin <pasha.tatashin@soleen.com>
Cc: Dan Williams <dan.j.williams@intel.com>
Acked-by: Michal Hocko <mhocko@suse.com>
Signed-off-by: David Hildenbrand <david@redhat.com>
---
 mm/memory_hotplug.c | 22 +++++++++-------------
 1 file changed, 9 insertions(+), 13 deletions(-)

diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
index f245fb50ba7f..01456fc66564 100644
--- a/mm/memory_hotplug.c
+++ b/mm/memory_hotplug.c
@@ -853,6 +853,7 @@ int __ref online_pages(unsigned long pfn, unsigned long nr_pages, int online_typ
 	ret = walk_system_ram_range(pfn, nr_pages, &onlined_pages,
 		online_pages_range);
 	if (ret) {
+		/* not a single memory resource was applicable */
 		if (need_zonelists_rebuild)
 			zone_pcp_reset(zone);
 		goto failed_addition;
@@ -866,27 +867,22 @@ int __ref online_pages(unsigned long pfn, unsigned long nr_pages, int online_typ
 
 	shuffle_zone(zone);
 
-	if (onlined_pages) {
-		node_states_set_node(nid, &arg);
-		if (need_zonelists_rebuild)
-			build_all_zonelists(NULL);
-		else
-			zone_pcp_update(zone);
-	}
+	node_states_set_node(nid, &arg);
+	if (need_zonelists_rebuild)
+		build_all_zonelists(NULL);
+	else
+		zone_pcp_update(zone);
 
 	init_per_zone_wmark_min();
 
-	if (onlined_pages) {
-		kswapd_run(nid);
-		kcompactd_run(nid);
-	}
+	kswapd_run(nid);
+	kcompactd_run(nid);
 
 	vm_total_pages = nr_free_pagecache_pages();
 
 	writeback_set_ratelimit();
 
-	if (onlined_pages)
-		memory_notify(MEM_ONLINE, &arg);
+	memory_notify(MEM_ONLINE, &arg);
 	mem_hotplug_done();
 	return 0;
 
-- 
2.21.0