linux-kernel - Re: [PATCH v6 6/6] mm/page_isolation: remove migratetype parameter from more functions.

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Message-ID: <25f660fc-a510-4dac-8f9c-1ab55be0b3d5@redhat.com>
Date: Mon, 2 Jun 2025 18:29:26 +0200
From: David Hildenbrand <david@...hat.com>
To: Zi Yan <ziy@...dia.com>
Cc: Johannes Weiner <hannes@...xchg.org>, Vlastimil Babka <vbabka@...e.cz>,
 linux-mm@...ck.org, Andrew Morton <akpm@...ux-foundation.org>,
 Oscar Salvador <osalvador@...e.de>,
 Baolin Wang <baolin.wang@...ux.alibaba.com>,
 "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
 Mel Gorman <mgorman@...hsingularity.net>,
 Suren Baghdasaryan <surenb@...gle.com>, Michal Hocko <mhocko@...e.com>,
 Brendan Jackman <jackmanb@...gle.com>, Richard Chang
 <richardycc@...gle.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v6 6/6] mm/page_isolation: remove migratetype parameter
 from more functions.

On 02.06.25 18:27, Zi Yan wrote:
> On 2 Jun 2025, at 12:25, David Hildenbrand wrote:
> 
>> On 02.06.25 16:18, Zi Yan wrote:
>>> On 30 May 2025, at 16:55, David Hildenbrand wrote:
>>>
>>>> On 30.05.25 22:46, Zi Yan wrote:
>>>>> On 30 May 2025, at 16:08, David Hildenbrand wrote:
>>>>>
>>>>>> On 30.05.25 21:58, Zi Yan wrote:
>>>>>>> On 30 May 2025, at 15:56, David Hildenbrand wrote:
>>>>>>>
>>>>>>>> On 30.05.25 18:22, 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 provide the information. At the
>>>>>>>>> same time change isolation flags to enum pb_isolate_mode
>>>>>>>>> (PB_ISOLATE_MODE_MEM_OFFLINE, PB_ISOLATE_MODE_CMA_ALLOC,
>>>>>>>>> PB_ISOLATE_MODE_OTHER). Remove REPORT_FAILURE and check
>>>>>>>>> MEMORY_OFFLINE instead, since only PB_ISOLATE_MODE_MEM_OFFLINE reports
>>>>>>>>> isolation failures.
>>>>>>>>>
>>>>>>>>> alloc_contig_range() no longer needs migratetype. Replace it with
>>>>>>>>> enum acr_flags_t to tell if an allocation is for CMA. So does
>>>>>>>>> __alloc_contig_migrate_range().
>>>>>>>>>
>>>>>>>>> Signed-off-by: Zi Yan <ziy@...dia.com>
>>>>>>>>> ---
>>>>>>>>>       drivers/virtio/virtio_mem.c    |  2 +-
>>>>>>>>>       include/linux/gfp.h            |  9 ++++-
>>>>>>>>>       include/linux/page-isolation.h | 20 ++++++++--
>>>>>>>>>       include/trace/events/kmem.h    | 14 ++++---
>>>>>>>>>       mm/cma.c                       |  2 +-
>>>>>>>>>       mm/memory_hotplug.c            |  6 +--
>>>>>>>>>       mm/page_alloc.c                | 27 ++++++-------
>>>>>>>>>       mm/page_isolation.c            | 70 +++++++++++++++-------------------
>>>>>>>>>       8 files changed, 82 insertions(+), 68 deletions(-)
>>>>>>>>>
>>>>>>>>> diff --git a/drivers/virtio/virtio_mem.c b/drivers/virtio/virtio_mem.c
>>>>>>>>> index 56d0dbe62163..6bce70b139b2 100644
>>>>>>>>> --- a/drivers/virtio/virtio_mem.c
>>>>>>>>> +++ b/drivers/virtio/virtio_mem.c
>>>>>>>>> @@ -1243,7 +1243,7 @@ static int virtio_mem_fake_offline(struct virtio_mem *vm, unsigned long pfn,
>>>>>>>>>       		if (atomic_read(&vm->config_changed))
>>>>>>>>>       			return -EAGAIN;
>>>>>>>>>      -		rc = alloc_contig_range(pfn, pfn + nr_pages, MIGRATE_MOVABLE,
>>>>>>>>> +		rc = alloc_contig_range(pfn, pfn + nr_pages, ACR_OTHER,
>>>>>>>>>       					GFP_KERNEL);
>>>>>>>>>       		if (rc == -ENOMEM)
>>>>>>>>>       			/* whoops, out of memory */
>>>>>>>>> diff --git a/include/linux/gfp.h b/include/linux/gfp.h
>>>>>>>>> index be160e8d8bcb..51990d571e3e 100644
>>>>>>>>> --- a/include/linux/gfp.h
>>>>>>>>> +++ b/include/linux/gfp.h
>>>>>>>>> @@ -423,9 +423,16 @@ static inline bool gfp_compaction_allowed(gfp_t gfp_mask)
>>>>>>>>>       extern gfp_t vma_thp_gfp_mask(struct vm_area_struct *vma);
>>>>>>>>>        #ifdef CONFIG_CONTIG_ALLOC
>>>>>>>>> +
>>>>>>>>> +enum acr_flags_t {
>>>>>>>>> +	ACR_CMA,	// CMA allocation
>>>>>>>>> +	ACR_OTHER,	// other allocation
>>>>>>>>> +};
>>>>>>>>
>>>>>>>> Hm, enum != flags.
>>>>>>>>
>>>>>>>> If you want to use flags, then just have ACR_CMA. ACR_OTHER is implied if not set.
>>>>>>>>
>>>>>>>> And ACR_CMA would then have to be "1" etc.
>>>>>>>
>>>>>>> I have a fixup to change acr_flags_t to acr_mode.
>>>>>>>
>>>>>>>>
>>>>>>>>> +
>>>>>>>>>       /* The below functions must be run on a range from a single zone. */
>>>>>>>>>       extern int alloc_contig_range_noprof(unsigned long start, unsigned long end,
>>>>>>>>> -			      unsigned migratetype, gfp_t gfp_mask);
>>>>>>>>> +				     enum acr_flags_t alloc_flags,
>>>>>>>>> +				     gfp_t gfp_mask);
>>>>>>>>>       #define alloc_contig_range(...)			alloc_hooks(alloc_contig_range_noprof(__VA_ARGS__))
>>>>>>>>>        extern struct page *alloc_contig_pages_noprof(unsigned long nr_pages, gfp_t gfp_mask,
>>>>>>>>> diff --git a/include/linux/page-isolation.h b/include/linux/page-isolation.h
>>>>>>>>> index 7a681a49e73c..3e2f960e166c 100644
>>>>>>>>> --- a/include/linux/page-isolation.h
>>>>>>>>> +++ b/include/linux/page-isolation.h
>>>>>>>>> @@ -38,8 +38,20 @@ static inline void set_pageblock_isolate(struct page *page)
>>>>>>>>>       }
>>>>>>>>>       #endif
>>>>>>>>>      -#define MEMORY_OFFLINE	0x1
>>>>>>>>> -#define REPORT_FAILURE	0x2
>>>>>>>>> +/*
>>>>>>>>> + * Pageblock isolation modes:
>>>>>>>>> + * PB_ISOLATE_MODE_MEM_OFFLINE - isolate to offline (!allocate) memory
>>>>>>>>> + *				 e.g., skip over PageHWPoison() pages and
>>>>>>>>> + *				 PageOffline() pages. Unmovable pages will be
>>>>>>>>> + *				 reported in this mode.
>>>>>>>>> + * PB_ISOLATE_MODE_CMA_ALLOC   - isolate for CMA allocations
>>>>>>>>> + * PB_ISOLATE_MODE_OTHER       - isolate for other purposes
>>>>>>>>> + */
>>>>>>>>> +enum pb_isolate_mode {
>>>>>>>>> +	PB_ISOLATE_MODE_MEM_OFFLINE,
>>>>>>>>> +	PB_ISOLATE_MODE_CMA_ALLOC,
>>>>>>>>> +	PB_ISOLATE_MODE_OTHER,
>>>>>>>>> +};
>>>>>>>>
>>>>>>>> It's late on friady, but it looks like we are duplicating things here.
>>>>>>>>
>>>>>>>> Let me think about that once my brain is recharged :)
>>>>>>>
>>>>>>> Sure. Take your time.
>>>>>>
>>>>>> Could we abstract both settings and use a single one? Then, we could simply reject if MEM_OFFLINE is passed into alloc_contig_range().
>>>>>>
>>>>>> alloc_contig_pages and page isolation, hmmmm, MEM_OFFLINE is kind-of an allocation. CMA is an allocation.
>>>>>>
>>>>>> Just an idea, not sure ...
>>>>>
>>>>> I think so.
>>>>>
>>>>> This is the fixup of removing acr_flags_t. It is on top of the original
>>>>> patch. Take your time. I guess I will send V7 with all fixups next week.
>>>>
>>>> Only wondering if we should rename "pb_isolate_mode" to something more abstract, that covers both use cases clearer.
>>>>
>>>> Hmmm.
>>>
>>> It is specifying the purpose of either alloc_contig_range() or
>>> test_pages_isolated(), but these two use cases do not have high level
>>> connection AFAICT.
>>
>> Hm, then maybe just keep it as is for now, and have the translation from ACP -> isolatetype.
>>
>> isolation modes should probably be an enum.
>>
>> acp might long-term benefit from flags, where we would essentially for now only have a single flag ("ACP_CMA").
> 
> OK, let me send a fixup to my V7.

Oh, I saw that v7 just now, sorry.

-- 
Cheers,

David / dhildenb