From: Zi Yan <ziy@nvidia.com>
To: Vlastimil Babka <vbabka@suse.cz>
Cc: David Hildenbrand <david@redhat.com>,
linux-mm@kvack.org, linux-kernel@vger.kernel.org,
Michael Ellerman <mpe@ellerman.id.au>,
Christoph Hellwig <hch@lst.de>,
Marek Szyprowski <m.szyprowski@samsung.com>,
Robin Murphy <robin.murphy@arm.com>,
linuxppc-dev@lists.ozlabs.org,
virtualization@lists.linux-foundation.org,
iommu@lists.linux-foundation.org
Subject: Re: [RFC PATCH 0/3] Use pageblock_order for cma and alloc_contig_range alignment.
Date: Mon, 29 Nov 2021 17:08:57 -0500 [thread overview]
Message-ID: <35A20739-152A-450E-8535-2236D2B28748@nvidia.com> (raw)
In-Reply-To: <52dbf824-76be-cc34-3983-d45510b1b618@suse.cz>
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On 23 Nov 2021, at 12:32, Vlastimil Babka wrote:
> On 11/23/21 17:35, Zi Yan wrote:
>> On 19 Nov 2021, at 10:15, Zi Yan wrote:
>>>>> From what my understanding, cma required alignment of
>>>>> max(MAX_ORDER - 1, pageblock_order), because when MIGRATE_CMA was introduced,
>>>>> __free_one_page() does not prevent merging two different pageblocks, when
>>>>> MAX_ORDER - 1 > pageblock_order. But current __free_one_page() implementation
>>>>> does prevent that.
>>>>
>>>> But it does prevent that only for isolated pageblock, not CMA, and yout
>>>> patchset doesn't seem to expand that to CMA? Or am I missing something.
>>>
>>> Yeah, you are right. Originally, I thought preventing merging isolated pageblock
>>> with other types of pageblocks is sufficient, since MIGRATE_CMA is always
>>> converted from MIGRATE_ISOLATE. But that is not true. I will rework the code.
>>> Thanks for pointing this out.
>>>
>>
>> I find that two pageblocks with different migratetypes, like MIGRATE_RECLAIMABLE
>> and MIGRATE_MOVABLE can be merged into a single free page after I checked
>> __free_one_page() in detail and printed pageblock information during buddy page
>> merging.
>
> Yes, that can happen.
>
> I am not sure what consequence it will cause. Do you have any idea?
>
> For MIGRATE_RECLAIMABLE or MIGRATE_MOVABLE or even MIGRATE_UNMOVABLE it's
> absolutely fine. As long as these pageblocks are fully free (and they are if
> it's a single free page spanning 2 pageblocks), they can be of any of these
> type, as they can be reused as needed without causing fragmentation.
>
> But in case of MIGRATE_CMA and MIGRATE_ISOLATE, uncontrolled merging would
> break the specifics of those types. That's why the code is careful for
> MIGRATE_ISOLATE, and MIGRATE_CMA was until now done in MAX_ORDER granularity.
Thanks for the explanation. Basically migratetypes that can fall back to each
other can be merged into a single free page, right?
How about MIGRATE_HIGHATOMIC? It should not be merged with other migratetypes
from my understanding.
--
Best Regards,
Yan, Zi
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next prev parent reply other threads:[~2021-11-29 22:09 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-11-15 19:37 [RFC PATCH 0/3] Use pageblock_order for cma and alloc_contig_range alignment Zi Yan
2021-11-15 19:37 ` [RFC PATCH 1/3] mm: cma: alloc_contig_range: use pageblock_order as the single alignment Zi Yan
2021-11-15 19:37 ` [RFC PATCH 2/3] drivers: virtio_mem: use pageblock size as the minimum virtio_mem size Zi Yan
2021-11-15 19:37 ` [RFC PATCH 3/3] arch: powerpc: adjust fadump alignment to be pageblock aligned Zi Yan
2021-11-15 19:37 ` [RFC PATCH 3/3] arch: powerpc: adjust fadump alignment to " Zi Yan
2021-11-16 8:58 ` [RFC PATCH 0/3] Use pageblock_order for cma and alloc_contig_range alignment David Hildenbrand
2021-11-17 3:04 ` Zi Yan
2021-11-23 16:54 ` David Hildenbrand
2021-11-19 12:33 ` Vlastimil Babka
2021-11-19 15:15 ` Zi Yan
2021-11-23 16:35 ` Zi Yan
2021-11-23 17:32 ` Vlastimil Babka
2021-11-29 22:08 ` Zi Yan [this message]
2021-11-30 9:11 ` Vlastimil Babka
2021-11-30 10:08 ` Mel Gorman
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