From mboxrd@z Thu Jan  1 00:00:00 1970
From: Michal Hocko <mhocko@suse.com>
Subject: Re: [PATCH RFC] mm/madvise: introduce MADV_POPULATE to
 prefault/prealloc memory
Date: Mon, 22 Feb 2021 15:02:31 +0100
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To: David Hildenbrand <david@redhat.com>
Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, Andrew Morton <akpm@linux-foundation.org>, Arnd Bergmann <arnd@arndb.de>, Oscar Salvador <osalvador@suse.de>, Matthew Wilcox <willy@infradead.org>, Andrea Arcangeli <aarcange@redhat.com>, Minchan Kim <minchan@kernel.org>, Jann Horn <jannh@google.com>, Jason Gunthorpe <jgg@ziepe.ca>, Dave Hansen <dave.hansen@intel.com>, Hugh Dickins <hughd@google.com>, Rik van Riel <riel@surriel.com>, "Michael S . Tsirkin" <mst@redhat.com>, "Kirill A . Shutemov" <kirill.shutemov@linux.intel.com>, Vlastimil Babka <vbabka@suse.cz>, Richard Henderson <rth@twiddle.net>, Ivan Kokshaysky <ink@jurassic.park.msu.ru>, Matt Turner <mattst88@gmail.com>, Thomas Bogendoerfer <tsbogend@alpha.franken.de>, James E.J. Bottomle

On Mon 22-02-21 14:22:37, David Hildenbrand wrote:
> > > Exactly. But for hugetlbfs/shmem ("!RAM-backed files") this is not what we
> > > want.
> > 
> > OK, then I must have misread your requirements. Maybe I just got lost in
> > all the combinations you have listed.
> 
> Another special case could be dax/pmem I think. You might want to fault it
> in readable/writable but not perform an actual read/write unless really
> required.
> 
> QEMU phrases this as "don't cause wear on the storage backing".

Sorry for being dense here but I still do not follow. If you do not want
to read then what do you want to populate from? Only map if it is in the
page cache?
-- 
Michal Hocko
SUSE Labs