Re: [RFC PATCH 4/4] mm/page_isolation: remove migratetype parameter from more functions.

[David Hildenbrand <david@redhat.com>]

On 04.09.24 04:02, Zi Yan wrote:
> On 2 Sep 2024, at 12:42, David Hildenbrand wrote:
> 
>> On 02.09.24 17:34, Zi Yan wrote:
>>> On 2 Sep 2024, at 5:06, David Hildenbrand wrote:
>>>
>>>> On 28.08.24 22:22, Zi Yan wrote:
>>>>> migratetype is no longer overwritten during pageblock isolation,
>>>>> start_isolate_page_range(), has_unmovable_pages(), and
>>>>> set_migratetype_isolate() no longer need which migratetype to restore
>>>>> during isolation failure. For has_unmoable_pages(), it needs to know if
>>>>> the isolation is for CMA allocation, so adding CMA_ALLOCATION to isolation
>>>>> flags to provide the information.
>>>>>
>>>>> Signed-off-by: Zi Yan <ziy@nvidia.com>
>>>>> ---
>>>>>     include/linux/page-isolation.h |  3 ++-
>>>>>     mm/memory_hotplug.c            |  1 -
>>>>>     mm/page_alloc.c                |  4 +++-
>>>>>     mm/page_isolation.c            | 27 +++++++++++----------------
>>>>>     4 files changed, 16 insertions(+), 19 deletions(-)
>>>>>
>>>>> diff --git a/include/linux/page-isolation.h b/include/linux/page-isolation.h
>>>>> index c2a1bd621561..e94117101b6c 100644
>>>>> --- a/include/linux/page-isolation.h
>>>>> +++ b/include/linux/page-isolation.h
>>>>> @@ -32,13 +32,14 @@ static inline bool is_migrate_isolate(int migratetype)
>>>>>      #define MEMORY_OFFLINE	0x1
>>>>>     #define REPORT_FAILURE	0x2
>>>>> +#define CMA_ALLOCATION	0x4
>>>>>      void set_pageblock_migratetype(struct page *page, int migratetype);
>>>>>      bool move_freepages_block_isolate(struct zone *zone, struct page *page);
>>>>>      int start_isolate_page_range(unsigned long start_pfn, unsigned long end_pfn,
>>>>> -			     int migratetype, int flags, gfp_t gfp_flags);
>>>>> +			     int flags, gfp_t gfp_flags);
>>>>>      void undo_isolate_page_range(unsigned long start_pfn, unsigned long end_pfn);
>>>>>    diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
>>>>> index 4265272faf4c..fe0b71e0f307 100644
>>>>> --- a/mm/memory_hotplug.c
>>>>> +++ b/mm/memory_hotplug.c
>>>>> @@ -1993,7 +1993,6 @@ int offline_pages(unsigned long start_pfn, unsigned long nr_pages,
>>>>>      	/* set above range as isolated */
>>>>>     	ret = start_isolate_page_range(start_pfn, end_pfn,
>>>>> -				       MIGRATE_MOVABLE,
>>>>>     				       MEMORY_OFFLINE | REPORT_FAILURE,
>>>>>     				       GFP_USER | __GFP_MOVABLE | __GFP_RETRY_MAYFAIL);
>>>>>     	if (ret) {
>>>>> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
>>>>> index 4d06932ba69a..c60bb95d7e65 100644
>>>>> --- a/mm/page_alloc.c
>>>>> +++ b/mm/page_alloc.c
>>>>> @@ -6607,7 +6607,9 @@ int alloc_contig_range_noprof(unsigned long start, unsigned long end,
>>>>>     	 * put back to page allocator so that buddy can use them.
>>>>>     	 */
>>>>>    -	ret = start_isolate_page_range(start, end, migratetype, 0, gfp_mask);
>>>>> +	ret = start_isolate_page_range(start, end,
>>>>> +			migratetype == MIGRATE_CMA ? CMA_ALLOCATION : 0,
>>>>
>>>> Can we have flags for alloc_contig_range() instead of passing in a (weird) migratetype?
>>>>
>>>> Then, we should make sure that we warn if we try a CMA allocation on any pageblock that is not of type CMA.
>>>
>>> Sure. I will expose the existing isolation flags (MEMORY_OFFLINE, REPORT_FAILURE,
>>> and CMA_ALLOCATION) as alloc_contig_range() parameter to replace migratetype one.
>>>
>>
>> Maybe we want some proper, distinct alloc_contig_range() falgs "acr_flags_t". Might be cleanest, to express anything that doesn't fall into the gfp_t flag category.
>>
>> Exposing MEMORY_OFFLINE feels wrong, for example.
> 
> OK, it seems that I mixed up of start_isolate_page_range() flags with
> alloc_contig_range() flags. Let me clarify them below.
> 
> For start_isolate_page_range(), memory offline calls it separately and
> needs MEMORY_OFFLINE and REPORT_FAILURE; CMA allocation uses it via
> alloc_contig_range() and needs a flag (like CMA_ALLOCATION) for its
> own checks.
> 
> BTW, it seems to me that MEMORY_OFFLINE and REPORT_FAILURE can be merged,
> since they are always used together. Let me know if you disagree.

I think there was a discussion about possibly using REPORT_FAILURE in 
other cases, but I agree that we might just merge them at this point.

> 
> For alloc_contig_range(), migratetype parameter is what you are talking about
> above. There are two callers: cma_alloc() and alloc_contig_pages().
> The acr_flags_t is basically a caller id. Something like?
> enum acr_flags_t {
> 	ACR_CMA_ALLOC,
> 	ACR_CONTIG_PAGES,
> };

I'd do something like:

typedef unsigned int __bitwise acr_flags_t;

#define ACR_CMA		((__force acr_flags_t)BIT(0))

No need for "ACR_CONTIG_PAGES", it's implicit if the CMA flag is not set.


> 
> And ACR_CMA_ALLOC needs to be translated to CMA_ALLOCATION when
> start_isolate_page_range() is called.

Yes.

> 
> BTW, after removing migratetype parameter from alloc_contig_range(),
> the tracepoint in __alloc_contig_migrate_range() needs to be changed to
> use acr_flags_t, since I do not think we want to convert acr_flags_t
> back to migratetype.

Sure, feel free to modify these tracepoints as it suits you.

-- 
Cheers,

David / dhildenb