linux-kernel - Re: [PATCH v4 0/4] Make alloc_contig

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Message-ID: <b04aaf5534f9ec0a40937e23a2500fdf@suse.de>
Date:   Wed, 17 Mar 2021 10:43:53 +0100
From:   Oscar Salvador <osalvador@...e.de>
To:     David Hildenbrand <david@...hat.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Vlastimil Babka <vbabka@...e.cz>,
        Michal Hocko <mhocko@...nel.org>,
        Muchun Song <songmuchun@...edance.com>,
        Mike Kravetz <mike.kravetz@...cle.com>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org,
        Anshuman Khandual <anshuman.khandual@....com>
Subject: Re: [PATCH v4 0/4] Make alloc_contig_range handle Hugetlb pages

On 2021-03-15 10:06, David Hildenbrand wrote:
> BTW, I stumbled yesterday over
> 
> alloc_contig_pages()->pfn_range_valid_contig():
> 
> 	if (page_count(page) > 0)
> 		rerurn false;
> 	if (PageHuge(page))
> 		return false;
> 
> As used by memtrace and for gigantic pages. We can now
> 
> a) Drop these check completely, as it's best-effort only and racy.
> alloc_contig_pages()/alloc_contig_range() will handle it properly.

I was preparing v5, and I wanted to be sure I understood you here.

Right you are that the in-use page check can be dropped, as those pages 
can
be migrated away, and the Hugetlb page check can also be dropped since
isolate_migratepages_range is now capable of dealing with those kind of 
pages.

> b) Similarly, check for gigantic pages and/or movability/migratability.

I lost you here.

isolate_or_dissolve_huge_page() already bails out on hugetlb-gigantic 
pages.

Or do you mean to place an upfront check here? (hstate_is_gigantic())?


-- 
Oscar Salvador
SUSE L3