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

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Message-ID: <dff8fa34-9099-46f9-b39a-1a986af2b022@redhat.com>
Date: Mon, 2 Sep 2024 18:42:06 +0200
From: David Hildenbrand <david@...hat.com>
To: Zi Yan <ziy@...dia.com>
Cc: linux-mm@...ck.org, Oscar Salvador <osalvador@...e.de>,
 Vlastimil Babka <vbabka@...e.cz>, Johannes Weiner <hannes@...xchg.org>,
 Baolin Wang <baolin.wang@...ux.alibaba.com>,
 "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
 Mel Gorman <mgorman@...e.de>, linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH 4/4] mm/page_isolation: remove migratetype parameter
 from more functions.

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@...dia.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.

>>
>> I'm trying to remember what happens if we try offlining a memory region that is of type MIGRATE_CMA right now ... I remember that we fail it. We should make sure that is still the case, otherwise we could seriously break something.
> 
> Yes, that fails. That is why I added CMA_ALLOCATION, which is used in
> has_unmovable_pages() for this situation.


Ah, okay I stumbled over that but wasn't sure if it gets the job done.

thanks!

-- 
Cheers,

David / dhildenb