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

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Message-ID: <756e456c-225b-4686-a3e5-09ee6f76453e@redhat.com>
Date: Mon, 2 Jun 2025 18:25:34 +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 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").

-- 
Cheers,

David / dhildenb