From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx148.postini.com [74.125.245.148]) by kanga.kvack.org (Postfix) with SMTP id 490466B005D for ; Wed, 11 Jul 2012 21:15:53 -0400 (EDT) Date: Thu, 12 Jul 2012 10:15:55 +0900 From: Minchan Kim Subject: Re: [PATCH 3/4] zsmalloc: add details to zs_map_object boiler plate Message-ID: <20120712011555.GB5503@bbox> References: <1341263752-10210-1-git-send-email-sjenning@linux.vnet.ibm.com> <1341263752-10210-4-git-send-email-sjenning@linux.vnet.ibm.com> <4FFB94FF.8030401@kernel.org> <4FFC478C.4050505@linux.vnet.ibm.com> <4FFD2E65.5080307@kernel.org> <4FFD8A8F.6030603@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <4FFD8A8F.6030603@linux.vnet.ibm.com> Sender: owner-linux-mm@kvack.org List-ID: To: Seth Jennings Cc: Greg Kroah-Hartman , Andrew Morton , Dan Magenheimer , Konrad Rzeszutek Wilk , Nitin Gupta , Robert Jennings , linux-mm@kvack.org, devel@driverdev.osuosl.org, linux-kernel@vger.kernel.org On Wed, Jul 11, 2012 at 09:15:43AM -0500, Seth Jennings wrote: > On 07/11/2012 02:42 AM, Minchan Kim wrote: > > On 07/11/2012 12:17 AM, Seth Jennings wrote: > >> On 07/09/2012 09:35 PM, Minchan Kim wrote: > >>> Maybe we need local_irq_save/restore in zs_[un]map_object path. > >> > >> I'd rather not disable interrupts since that will create > >> unnecessary interrupt latency for all users, even if they > > > > Agreed. > > Although we guide k[un]map atomic is so fast, it isn't necessary > > to force irq_[enable|disable]. Okay. > > > >> don't need interrupt protection. If a particular user uses > >> zs_map_object() in an interrupt path, it will be up to that > >> user to disable interrupts to ensure safety. > > > > Nope. It shouldn't do that. > > Any user in interrupt context can't assume that there isn't any other user using per-cpu buffer > > right before interrupt happens. > > > > The concern is that if such bug happens, it's very hard to find a bug. > > So, how about adding this? > > > > void zs_map_object(...) > > { > > BUG_ON(in_interrupt()); > > } > > I not completely following you, but I think I'm following > enough. Your point is that the per-cpu buffers are shared > by all zsmalloc users and one user doesn't know if another > user is doing a zs_map_object() in an interrupt path. And vise versa is yes. > > However, I think what you are suggesting is to disallow > mapping in interrupt context. This is a problem for zcache > as it already does mapping in interrupt context, namely for > page decompression in the page fault handler. I don't get it. Page fault handler isn't interrupt context. > > What do you think about making the per-cpu buffers local to > each zsmalloc pool? That way each user has their own per-cpu > buffers and don't step on each other's toes. Maybe, It could be a solution if you really need it in interrupt context. But the concern is it could hurt zsmalloc's goal which is memory space efficiency if your system has lots of CPUs. > > Thanks, > Seth > > -- > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html > Please read the FAQ at http://www.tux.org/lkml/ -- 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