From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pb0-f48.google.com (mail-pb0-f48.google.com [209.85.160.48]) by kanga.kvack.org (Postfix) with ESMTP id 7D1D16B0037 for ; Mon, 7 Oct 2013 19:27:26 -0400 (EDT) Received: by mail-pb0-f48.google.com with SMTP id ma3so7640781pbc.7 for ; Mon, 07 Oct 2013 16:27:26 -0700 (PDT) Message-ID: <52534331.2060402@zytor.com> Date: Mon, 07 Oct 2013 16:26:41 -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> <52533C12.9090007@zytor.com> <5253404D.2030503@linaro.org> In-Reply-To: <5253404D.2030503@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 10/07/2013 04:14 PM, John Stultz wrote: >> >> 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. > > The reason we can't use madvise, is that to properly handle error cases > and report the pruge state, we need an extra argument. > > In much earlier versions, we just returned an error when setting > NONVOLATILE if the data was purged. However, since we have to possibly > do allocations when marking a range as non-volatile, we needed a way to > properly handle that allocation failing. We can't just return ENOMEM, as > we may have already marked purged memory as non-volatile. > > Thus, that's why with vrange, we return the number of bytes modified, > along with the purge state. That way, if an error does occur we can > return the purge state of the bytes successfully modified, and only > return an error if nothing was changed, much like when a write fails. > I am not clear at all what the "purge state" is in this case. -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