linux-kernel - Re: [sample] mem_notify v6: usage example

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Message-id: <20080211181526.GC3029@webber.adilger.int>
Date:	Mon, 11 Feb 2008 11:15:26 -0700
From:	Andreas Dilger <adilger@....com>
To:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
Cc:	Jon Masters <jonathan@...masters.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Marcelo Tosatti <marcelo@...ck.org>,
	Daniel Spang <daniel.spang@...il.com>,
	Rik van Riel <riel@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	"linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
	Pavel Machek <pavel@....cz>, Al Boldi <a1426z@...ab.com>,
	Zan Lynx <zlynx@....org>
Subject: Re: [sample] mem_notify v6: usage example

On Feb 10, 2008  01:46 +0900, KOSAKI Motohiro wrote:
> > This really needs to be triggered via a generic kernel event in the
> > final version - I picture glibc having a reservation API and having
> > generic support for freeing such reservations.
> 
> to be honest, I doubt idea of generic reservation framework.
> 
> end up, we hope drop the application cache, not also dataless memory.
> but, automatically drop mechanism only able to drop dataless memory.
> 
> and, many application have own memory management subsystem.
> I afraid to nobody use too complex framework.

Having such notification handled by glibc to free up unused malloc (or
any heap allocations) would be very useful, because even if a program
does "free" there is no guarantee the memory is returned to the kernel.

I think that having a generic reservation framework is too complex, but
hiding the details of /dev/mem_notify from applications is desirable.
A simple wrapper (possibly part of glibc) to return the poll fd, or set
up the signal is enough.

Cheers, Andreas
--
Andreas Dilger
Sr. Staff Engineer, Lustre Group
Sun Microsystems of Canada, Inc.

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