linux-kernel - Re: [RFC] Re: Costless huge virtual memory? /dev/same, /dev/null?

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Message-ID: <20170413163411.GH784@bombadil.infradead.org>
Date:   Thu, 13 Apr 2017 09:34:11 -0700
From:   Matthew Wilcox <willy@...radead.org>
To:     Samuel Thibault <samuel.thibault@...-lyon.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Arnd Bergmann <arnd@...db.de>, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org
Subject: Re: [RFC] Re: Costless huge virtual memory? /dev/same, /dev/null?

On Thu, Apr 13, 2017 at 06:29:46PM +0200, Samuel Thibault wrote:
> (Ideally we'd be able to take the MAP_HUGETLB mmap flag into account to
> map a single huge page repeatedly, even lowering the populating cost,
> but AIUI of the current hugepage support it would be far from easy)

You could implement ->map_pages instead of (or as well as) ->fault, which
would lower your costs if that is a concern.  I think the eventual intent
is that map_pages would be able to populate a PMD or even a PUD.