linux-kernel - Re: [PATCH] mm/page_alloc: Skip non present sections on zone initialization

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Message-ID: <73437651-822f-fcec-3b96-281fb1064cf8@redhat.com>
Date:   Fri, 10 Jan 2020 14:15:26 +0100
From:   David Hildenbrand <david@...hat.com>
To:     Michal Hocko <mhocko@...nel.org>,
        "Kirill A. Shutemov" <kirill@...temov.name>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Dan Williams <dan.j.williams@...el.com>,
        Vlastimil Babka <vbabka@...e.cz>, Mel Gorman <mgorman@...e.de>,
        "Jin, Zhi" <zhi.jin@...el.com>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
Subject: Re: [PATCH] mm/page_alloc: Skip non present sections on zone
 initialization

On 08.01.20 15:40, Michal Hocko wrote:
> On Mon 30-12-19 12:38:28, Kirill A. Shutemov wrote:
>> memmap_init_zone() can be called on the ranges with holes during the
>> boot. It will skip any non-valid PFNs one-by-one. It works fine as long
>> as holes are not too big.
>>
>> But huge holes in the memory map causes a problem. It takes over 20
>> seconds to walk 32TiB hole. x86-64 with 5-level paging allows for much
>> larger holes in the memory map which would practically hang the system.
>>
>> Deferred struct page init doesn't help here. It only works on the
>> present ranges.
>>
>> Skipping non-present sections would fix the issue.
> 
> Makes sense to me.
> 
>> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
> 
> That pfn inc back and forth is quite ugly TBH but whatever.

Indeed, can we please rewrite the loop to fix that?


-- 
Thanks,

David / dhildenb