linux-kernel - Re: [PATCH 5/8] vrange: Add new vrange(2) system call

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Date:	Thu, 20 Jun 2013 17:05:21 -0400
From:	Dhaval Giani <dgiani@...illa.com>
To:	John Stultz <john.stultz@...aro.org>
CC:	LKML <linux-kernel@...r.kernel.org>,
	Minchan Kim <minchan@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Android Kernel Team <kernel-team@...roid.com>,
	Robert Love <rlove@...gle.com>, Mel Gorman <mel@....ul.ie>,
	Hugh Dickins <hughd@...gle.com>,
	Dave Hansen <dave@...ux.vnet.ibm.com>,
	Rik van Riel <riel@...hat.com>,
	Dmitry Adamushko <dmitry.adamushko@...il.com>,
	Dave Chinner <david@...morbit.com>, Neil Brown <neilb@...e.de>,
	Andrea Righi <andrea@...terlinux.com>,
	Andrea Arcangeli <aarcange@...hat.com>,
	"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>,
	Mike Hommey <mh@...ndium.org>, Taras Glek <tglek@...illa.com>,
	Jan Kara <jack@...e.cz>,
	KOSAKI Motohiro <kosaki.motohiro@...il.com>,
	Michel Lespinasse <walken@...gle.com>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>
Subject: Re: [PATCH 5/8] vrange: Add new vrange(2) system call

On 2013-06-12 12:22 AM, John Stultz wrote:
> From: Minchan Kim <minchan@...nel.org>
>
> This patch adds new system call sys_vrange.
>
> NAME
> 	vrange - Mark or unmark range of memory as volatile
>
> SYNOPSIS
> 	int vrange(unsigned_long start, size_t length, int mode,
> 			 int *purged);
>
> DESCRIPTION
> 	Applications can use vrange(2) to advise the kernel how it should
> 	handle paging I/O in this VM area.  The idea is to help the kernel
> 	discard pages of vrange instead of reclaiming when memory pressure
> 	happens. It means kernel doesn't discard any pages of vrange if
> 	there is no memory pressure.
>
> 	mode:
> 	VRANGE_VOLATILE
> 		hint to kernel so VM can discard in vrange pages when
> 		memory pressure happens.
> 	VRANGE_NONVOLATILE
> 		hint to kernel so VM doesn't discard vrange pages
> 		any more.
>
> 	If user try to access purged memory without VRANGE_NOVOLATILE call,
> 	he can encounter SIGBUS if the page was discarded by kernel.

I wonder if it would be possible to provide additional information here, 
for example "purge range at a time" as opposed to "purge page at a 
time". There are some valid use cases for both approaches and it doesn't 
make sense to deny one use case.

Thanks!
Dhaval
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