[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Message-ID: <BF8FB68A-6E1D-4465-8A2B-884FC034660B@nvidia.com>
Date: Tue, 23 Nov 2021 11:35:06 -0500
From: Zi Yan <ziy@...dia.com>
To: Vlastimil Babka <vbabka@...e.cz>
Cc: David Hildenbrand <david@...hat.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
Subject: Re: [RFC PATCH 0/3] Use pageblock_order for cma and alloc_contig_range alignment.
On 19 Nov 2021, at 10:15, Zi Yan wrote:
> On 19 Nov 2021, at 7:33, Vlastimil Babka wrote:
>
>> On 11/15/21 20:37, Zi Yan wrote:
>>> From: Zi Yan <ziy@...dia.com>
>>>
>>> Hi David,
>>>
>>> You suggested to make alloc_contig_range() deal with pageblock_order instead of
>>> MAX_ORDER - 1 and get rid of MAX_ORDER - 1 dependency in virtio_mem[1]. This
>>> patchset is my attempt to achieve that. Please take a look and let me know if
>>> I am doing it correctly or not.
>>>
>>> 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. I am not sure what consequence it will cause. Do you have any idea?
I will fix it in the next version of this patchset.
>>
>>
>>> It should be OK to just align cma to pageblock_order.
>>> alloc_contig_range() relies on MIGRATE_CMA to get free pages, so it can use
>>> pageblock_order as alignment too.
>>>
>>> In terms of virtio_mem, if I understand correctly, it relies on
>>> alloc_contig_range() to obtain contiguous free pages and offlines them to reduce
>>> guest memory size. As the result of alloc_contig_range() alignment change,
>>> virtio_mem should be able to just align PFNs to pageblock_order.
>>>
>>> Thanks.
>>>
>>>
>>> [1] https://lore.kernel.org/linux-mm/28b57903-fae6-47ac-7e1b-a1dd41421349@redhat.com/
>>>
>>> Zi Yan (3):
>>> mm: cma: alloc_contig_range: use pageblock_order as the single
>>> alignment.
>>> drivers: virtio_mem: use pageblock size as the minimum virtio_mem
>>> size.
>>> arch: powerpc: adjust fadump alignment to be pageblock aligned.
>>>
>>> arch/powerpc/include/asm/fadump-internal.h | 4 +---
>>> drivers/virtio/virtio_mem.c | 6 ++----
>>> include/linux/mmzone.h | 5 +----
>>> kernel/dma/contiguous.c | 2 +-
>>> mm/cma.c | 6 ++----
>>> mm/page_alloc.c | 12 +++++-------
>>> 6 files changed, 12 insertions(+), 23 deletions(-)
>>>
>
> --
> Best Regards,
> Yan, Zi
--
Best Regards,
Yan, Zi
Download attachment "signature.asc" of type "application/pgp-signature" (855 bytes)
Powered by blists - more mailing lists