linux-kernel - Re: [PATCH v5 5/5] mm,page_alloc: Drop unnecessary checks from pfn_range_valid

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Message-ID: <ef5560a4-8633-39bd-e433-6aa8f6ea4bfc@redhat.com>
Date:   Wed, 17 Mar 2021 15:36:35 +0100
From:   David Hildenbrand <david@...hat.com>
To:     Michal Hocko <mhocko@...e.com>, Oscar Salvador <osalvador@...e.de>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Vlastimil Babka <vbabka@...e.cz>,
        Muchun Song <songmuchun@...edance.com>,
        Mike Kravetz <mike.kravetz@...cle.com>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v5 5/5] mm,page_alloc: Drop unnecessary checks from
 pfn_range_valid_contig

On 17.03.21 15:31, Michal Hocko wrote:
> On Wed 17-03-21 12:12:51, Oscar Salvador wrote:
>> pfn_range_valid_contig() bails out when it finds an in-use page or a
>> hugetlb page, among other things.
>> We can drop the in-use page check since __alloc_contig_pages can migrate
>> away those pages, and the hugetlb page check can go too since
>> isolate_migratepages_range is now capable of dealing with hugetlb pages.
>> Either way, those checks are racy so let the end function handle it
>> when the time comes.
> 
> I haven't realized PageHuge check is done this early. This means that
> previous patches are not actually active until now which is not really
> greate for bisectability. Can we remove the HugePage check earlier?

alloc_contig_pages() vs. alloc_contig_range(). The patches are active 
for virtio-mem and CMA AFAIKS.

-- 
Thanks,

David / dhildenb