linux-kernel - Re: [PATCH 2/3] mm: introduce fincore()

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Date:	Mon, 02 Jun 2014 09:11:37 -0700
From:	Dave Hansen <dave.hansen@...el.com>
To:	Naoya Horiguchi <n-horiguchi@...jp.nec.com>,
	Andrew Morton <akpm@...ux-foundation.org>
CC:	Konstantin Khlebnikov <koct9i@...il.com>,
	Wu Fengguang <fengguang.wu@...el.com>,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	Borislav Petkov <bp@...en8.de>,
	"Kirill A. Shutemov" <kirill@...temov.name>,
	Johannes Weiner <hannes@...xchg.org>,
	Rusty Russell <rusty@...tcorp.com.au>,
	David Miller <davem@...emloft.net>,
	Andres Freund <andres@...quadrant.com>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
Subject: Re: [PATCH 2/3] mm: introduce fincore()

On 06/01/2014 10:24 PM, Naoya Horiguchi wrote:
> Detail about the data format being passed to userspace are explained in
> inline comment, but generally in long entry format, we can choose which
> information is extraced flexibly, so you don't have to waste memory by
> extracting unnecessary information. And with FINCORE_SKIP_HOLE flag,
> we can skip hole pages (not on memory,) which makes us avoid a flood of
> meaningless zero entries when calling on extremely large (but only few
> pages of it are loaded on memory) file.

Something similar could be useful for hugetlbfs too.  For a 1GB page,
it's pretty silly to do 2^18 entries which essentially repeat the same
data in an interface like this.
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