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

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Message-ID: <50da1626-5894-42ef-b3fd-935a331f14c4@redhat.com>
Date: Fri, 30 May 2025 22:08:58 +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 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 ...

-- 
Cheers,

David / dhildenb