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

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Message-ID: <20200110134547.v6ju5dxazknfjdj3@box>
Date:   Fri, 10 Jan 2020 16:45:47 +0300
From:   "Kirill A. Shutemov" <kirill@...temov.name>
To:     David Hildenbrand <david@...hat.com>
Cc:     Michal Hocko <mhocko@...nel.org>,
        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 Fri, Jan 10, 2020 at 02:15:26PM +0100, David Hildenbrand wrote:
> 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?

Any suggestions?

I don't see an obvious way to not break readablity in another place.

-- 
 Kirill A. Shutemov