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


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