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

[Dhaval Giani <dgiani@mozilla.com>]

On 2013-06-12 12:22 AM, John Stultz wrote:
> From: Minchan Kim <minchan@kernel.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