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

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Message-ID: <87621skhtc.fsf@rustcorp.com.au>
Date:	Sat, 16 Feb 2013 14:53:43 +1030
From:	Rusty Russell <rusty@...tcorp.com.au>
To:	Andrew Morton <akpm@...ux-foundation.org>,
	Johannes Weiner <hannes@...xchg.org>
Cc:	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()

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.

I'd really like to use it for backup programs, so they stop pulling
random crap into memory (but leave things already resident).  But that
needs to madvise(MADV_DONTNEED) on the page, so need mmap.

So why not just use mincore?

Cheers,
Rusty.
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