From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx198.postini.com [74.125.245.198]) by kanga.kvack.org (Postfix) with SMTP id 6DA686B004F for ; Tue, 24 Jan 2012 11:23:19 -0500 (EST) From: Arnd Bergmann Subject: Re: [RFC 1/3] /dev/low_mem_notify Date: Tue, 24 Jan 2012 16:22:36 +0000 References: <1326788038-29141-1-git-send-email-minchan@kernel.org> <84FF21A720B0874AA94B46D76DB98269045596AE@008-AM1MPN1-003.mgdnok.nokia.com> In-Reply-To: MIME-Version: 1.0 Content-Type: Text/Plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit Message-Id: <201201241622.36222.arnd@arndb.de> Sender: owner-linux-mm@kvack.org List-ID: To: Pekka Enberg Cc: leonid.moiseichuk@nokia.com, riel@redhat.com, minchan@kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, kamezawa.hiroyu@jp.fujitsu.com, mel@csn.ul.ie, rientjes@google.com, kosaki.motohiro@gmail.com, hannes@cmpxchg.org, mtosatti@redhat.com, akpm@linux-foundation.org, rhod@redhat.com, kosaki.motohiro@jp.fujitsu.com On Wednesday 18 January 2012, Pekka Enberg wrote: > >> +struct vmnotify_event { > >> + /* Size of the struct for ABI extensibility. */ > >> + __u32 size; > >> + > >> + __u64 nr_avail_pages; > >> + > >> + __u64 nr_swap_pages; > >> + > >> + __u64 nr_free_pages; > >> +}; > > > > Two fields here most likely session-constant, (nr_avail_pages and > > nr_swap_pages), seems not much sense to report them in every event. If we > > have memory/swap hotplug user-space can use sysinfo() call. > > I actually changed the ABI to look like this: > > struct vmnotify_event { > /* > * Size of the struct for ABI extensibility. > */ > __u32 size; > > __u64 attrs; > > __u64 attr_values[]; > }; > > So userspace can decide which fields to include in notifications. Please make the first member a __u64 instead of a __u32. This will avoid incompatibility between 32 and 64 bit processes, which have different alignment rules on x86: x86-32 would implicitly pack the struct while x86-64 would add padding with your layout. Arnd -- 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/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: email@kvack.org