linux-kernel - Re: [patch 1/2] mm: fincore()

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Message-ID: <20130529145312.GE3955@alap2.anarazel.de>
Date:	Wed, 29 May 2013 16:53:12 +0200
From:	Andres Freund <andres@...quadrant.com>
To:	Rusty Russell <rusty@...tcorp.com.au>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Johannes Weiner <hannes@...xchg.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Nick Piggin <npiggin@...e.de>,
	Stewart Smith <stewart@...mingspork.com>, linux-mm@...ck.org,
	linux-arch@...r.kernel.org
Subject: Re: [patch 1/2] mm: fincore()

On 2013-02-16 14:53:43 +1030, Rusty Russell wrote:
> Andrew Morton <akpm@...ux-foundation.org> writes:
> > On Fri, 15 Feb 2013 18:13:04 -0500
> > Johannes Weiner <hannes@...xchg.org> wrote:
> >> I dunno.  The byte vector might not be optimal but its worst cases
> >> seem more attractive, is just as extensible, and dead simple to use.
> >
> > But I think "which pages from this 4TB file are in core" will not be an
> > uncommon usage, and writing a gig of memory to find three pages is just
> > awful.
> 
> Actually, I don't know of any usage for this call.

[months later, catching up]

I do. Postgres' could really use something like that for making saner
assumptions about the cost of doing an index/heap scan. postgres doesn't
use mmap() and mmaping larger files into memory isn't all that cheap
(32bit...) so having fincore would be nice.

Greetings,

Andres Freund

-- 
 Andres Freund	                   http://www.2ndQuadrant.com/
 PostgreSQL Development, 24x7 Support, Training & Services
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