linux-kernel - Re: [PATCH V2] mm/page_alloc: Add alloc_contig

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Message-ID: <0ce85182-e00c-8748-32f7-89c30b3be35b@oracle.com>
Date:   Wed, 16 Oct 2019 17:50:09 -0700
From:   Mike Kravetz <mike.kravetz@...cle.com>
To:     Anshuman Khandual <anshuman.khandual@....com>, linux-mm@...ck.org
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Vlastimil Babka <vbabka@...e.cz>,
        Michal Hocko <mhocko@...e.com>,
        David Rientjes <rientjes@...gle.com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Oscar Salvador <osalvador@...e.de>,
        Mel Gorman <mgorman@...hsingularity.net>,
        Mike Rapoport <rppt@...ux.ibm.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Pavel Tatashin <pavel.tatashin@...rosoft.com>,
        Matthew Wilcox <willy@...radead.org>,
        David Hildenbrand <david@...hat.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH V2] mm/page_alloc: Add alloc_contig_pages()

On 10/16/19 4:02 AM, Anshuman Khandual wrote:
> HugeTLB helper alloc_gigantic_page() implements fairly generic allocation
> method where it scans over various zones looking for a large contiguous pfn
> range before trying to allocate it with alloc_contig_range(). Other than
> deriving the requested order from 'struct hstate', there is nothing HugeTLB
> specific in there. This can be made available for general use to allocate
> contiguous memory which could not have been allocated through the buddy
> allocator.
> 
> alloc_gigantic_page() has been split carving out actual allocation method
> which is then made available via new alloc_contig_pages() helper wrapped
> under CONFIG_CONTIG_ALLOC. All references to 'gigantic' have been replaced
> with more generic term 'contig'. Allocated pages here should be freed with
> free_contig_range() or by calling __free_page() on each allocated page.

I had a 'test harness' used when previously working on such an interface.
It simply provides a user interface to call the allocator with random
values for nr_pages.  Several tasks are then started doing random allocations
in parallel.  The new interface is pretty straight forward, but the idea
was to stress the underlying code.  In fact, it did identify issues with
isolation which were corrected.

I exercised this new interface in the same way and am happy to report that
no issues were detected.
-- 
Mike Kravetz