linux-kernel - Re: [RFC PATCH v3 1/8] mm: page_alloc: avoid merging non-fallbackable pageblocks with others.

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Message-ID: <ae2862a0-c39c-ed2f-23fe-510c6c2fad5c@redhat.com>
Date:   Thu, 13 Jan 2022 13:28:11 +0100
From:   David Hildenbrand <david@...hat.com>
To:     Mike Rapoport <rppt@...nel.org>
Cc:     Zi Yan <ziy@...dia.com>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org,
        Michael Ellerman <mpe@...erman.id.au>,
        Christoph Hellwig <hch@....de>,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        Robin Murphy <robin.murphy@....com>,
        linuxppc-dev@...ts.ozlabs.org,
        virtualization@...ts.linux-foundation.org,
        iommu@...ts.linux-foundation.org, Vlastimil Babka <vbabka@...e.cz>,
        Mel Gorman <mgorman@...hsingularity.net>,
        Eric Ren <renzhengeek@...il.com>
Subject: Re: [RFC PATCH v3 1/8] mm: page_alloc: avoid merging non-fallbackable
 pageblocks with others.

On 13.01.22 12:36, Mike Rapoport wrote:
> On Wed, Jan 12, 2022 at 11:54:49AM +0100, David Hildenbrand wrote:
>> On 05.01.22 22:47, Zi Yan wrote:
>>> From: Zi Yan <ziy@...dia.com>
>>>
>>> This is done in addition to MIGRATE_ISOLATE pageblock merge avoidance.
>>> It prepares for the upcoming removal of the MAX_ORDER-1 alignment
>>> requirement for CMA and alloc_contig_range().
>>>
>>> MIGRARTE_HIGHATOMIC should not merge with other migratetypes like
>>> MIGRATE_ISOLATE and MIGRARTE_CMA[1], so this commit prevents that too.
>>> Also add MIGRARTE_HIGHATOMIC to fallbacks array for completeness.
>>>
>>> [1] https://lore.kernel.org/linux-mm/20211130100853.GP3366@techsingularity.net/
>>>
>>> Signed-off-by: Zi Yan <ziy@...dia.com>
>>> ---
>>>  include/linux/mmzone.h |  6 ++++++
>>>  mm/page_alloc.c        | 28 ++++++++++++++++++----------
>>>  2 files changed, 24 insertions(+), 10 deletions(-)
>>>
> 
> ...
> 
>>> @@ -3545,8 +3553,8 @@ int __isolate_free_page(struct page *page, unsigned int order)
>>>  		struct page *endpage = page + (1 << order) - 1;
>>>  		for (; page < endpage; page += pageblock_nr_pages) {
>>>  			int mt = get_pageblock_migratetype(page);
>>> -			if (!is_migrate_isolate(mt) && !is_migrate_cma(mt)
>>> -			    && !is_migrate_highatomic(mt))
>>> +			/* Only change normal pageblock */
>>> +			if (migratetype_has_fallback(mt))
>>>  				set_pageblock_migratetype(page,
>>>  							  MIGRATE_MOVABLE);
>>>  		}
>>
>> That part is a nice cleanup IMHO. Although the "has fallback" part is a
>> bit imprecise. "migratetype_is_mergable()" might be a bit clearer.
>> ideally "migratetype_is_mergable_with_other_types()". Can we come up
>> with a nice name for that?
> 
> migratetype_is_mergable() kinda implies "_with_other_types", no?
> 
> I like migratetype_is_mergable() more than _has_fallback().
> 
> My $0.02 to bikeshedding :)

:)

Yeah, for me migratetype_is_mergable() would also be good enough. I
think I was at first thinking one could mistake it with a dedicated
migratetype. But such functions are historically called

is_migrate_cma/is_migrate_cma/....

-- 
Thanks,

David / dhildenb