linux-kernel - Re: [RFC PATCH v3 3/8] mm: migrate: allocate the right size of non hugetlb or THP compound pages.

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Message-ID: <5da2e9ae-24bc-a146-053d-a43063bad73e@redhat.com>
Date:   Thu, 13 Jan 2022 16:50:29 +0100
From:   David Hildenbrand <david@...hat.com>
To:     Zi Yan <ziy@...dia.com>
Cc:     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 3/8] mm: migrate: allocate the right size of non
 hugetlb or THP compound pages.

On 13.01.22 16:46, Zi Yan wrote:
> On 12 Jan 2022, at 6:04, David Hildenbrand wrote:
> 
>> On 05.01.22 22:47, Zi Yan wrote:
>>> From: Zi Yan <ziy@...dia.com>
>>>
>>> alloc_migration_target() is used by alloc_contig_range() and non-LRU
>>> movable compound pages can be migrated. Current code does not allocate the
>>> right page size for such pages. Check THP precisely using
>>> is_transparent_huge() and add allocation support for non-LRU compound
>>> pages.
>>
>> IIRC, we don't have any non-lru migratable pages that are coumpound
>> pages. Read: not used and not supported :)
> 
> OK, but nothing prevents one writing a driver that allocates compound
> pages and provides address_space->migratepage() and address_space->isolate_page().
> 
> Actually, to test this series, I write a kernel module that allocates
> an order-10 page, gives it a fake address_space with migratepage() and
> isolate_page(), __SetPageMovable() on it, then call alloc_contig_range()
> on the page range. Apparently, my kernel module is not supported by
> the kernel, thus, I added this patch.
> 
> Do you have an alternative test to my kernel module, so that I do not
> even need this patch myself?
> 
>> Why is this required in the context of this series?
> 
> It might not be required. I will drop it.

That's why I think it would be best dropping it. If you need it in
different context, better submit it in different context.

Makes this series easier to digest :)


-- 
Thanks,

David / dhildenb