From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pb0-f53.google.com (mail-pb0-f53.google.com [209.85.160.53]) by kanga.kvack.org (Postfix) with ESMTP id A03436B0037 for ; Mon, 7 Oct 2013 18:57:10 -0400 (EDT) Received: by mail-pb0-f53.google.com with SMTP id up15so7696844pbc.40 for ; Mon, 07 Oct 2013 15:57:10 -0700 (PDT) Message-ID: <52533C12.9090007@zytor.com> Date: Mon, 07 Oct 2013 15:56:18 -0700 From: "H. Peter Anvin" MIME-Version: 1.0 Subject: Re: [PATCH 05/14] vrange: Add new vrange(2) system call References: <1380761503-14509-1-git-send-email-john.stultz@linaro.org> <1380761503-14509-6-git-send-email-john.stultz@linaro.org> In-Reply-To: <1380761503-14509-6-git-send-email-john.stultz@linaro.org> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: John Stultz Cc: LKML , Minchan Kim , Andrew Morton , Android Kernel Team , Robert Love , Mel Gorman , Hugh Dickins , Dave Hansen , Rik van Riel , Dmitry Adamushko , Dave Chinner , Neil Brown , Andrea Righi , Andrea Arcangeli , "Aneesh Kumar K.V" , Mike Hommey , Taras Glek , Dhaval Giani , Jan Kara , KOSAKI Motohiro , Michel Lespinasse , Rob Clark , "linux-mm@kvack.org" On 10/02/2013 05:51 PM, John Stultz wrote: > From: Minchan Kim > > This patch adds new system call sys_vrange. > > NAME > vrange - Mark or unmark range of memory as volatile > vrange() is about as nondescriptive as one can get -- there is exactly one letter that has any connection with that this does. > 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. > > purged: Pointer to an integer which will return 1 if > mode == VRANGE_NONVOLATILE and any page in the affected range > was purged. If purged returns zero during a mode == > VRANGE_NONVOLATILE call, it means all of the pages in the range > are intact. I'm a bit confused about the "purged" >>From an earlier version of the patch: > - What's different with madvise(DONTNEED)? > > System call semantic > > DONTNEED makes sure user always can see zero-fill pages after > he calls madvise while vrange can see data or encounter SIGBUS. This difference doesn't seem to be a huge one. The other one seems to be the blocking status of MADV_DONTNEED, which perhaps may be better handled by adding an option (MADV_LAZY) perhaps? That way we would have lazy vs. immediate, and zero versus SIGBUS. I see from the change history of the patch that this was an madvise() at some point, but was changed into a separate system call at some point, does anyone remember why that was? A quick look through my LKML archives doesn't really make it clear. -hpa -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org