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

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Message-ID: <BDD48C59-0C42-4B1E-A4F3-FF97744FCF6D@nvidia.com>
Date: Tue, 03 Sep 2024 22:02:32 -0400
From: Zi Yan <ziy@...dia.com>
To: David Hildenbrand <david@...hat.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 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@...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.

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.

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,
};

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

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.


Best Regards,
Yan, Zi

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