From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755993AbbAZUQQ (ORCPT ); Mon, 26 Jan 2015 15:16:16 -0500 Received: from mx2.parallels.com ([199.115.105.18]:33201 "EHLO mx2.parallels.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753120AbbAZUQM (ORCPT ); Mon, 26 Jan 2015 15:16:12 -0500 Date: Mon, 26 Jan 2015 23:16:02 +0300 From: Vladimir Davydov To: Christoph Lameter CC: Andrew Morton , Pekka Enberg , David Rientjes , Joonsoo Kim , Johannes Weiner , Michal Hocko , , Subject: Re: [PATCH -mm 2/3] slab: zap kmem_cache_shrink return value Message-ID: <20150126201602.GA3317@esperanza> References: <20150126170418.GC28978@esperanza> <20150126194838.GB2660@esperanza> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Disposition: inline In-Reply-To: Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Jan 26, 2015 at 01:55:14PM -0600, Christoph Lameter wrote: > On Mon, 26 Jan 2015, Vladimir Davydov wrote: > > > Hmm, why? The return value has existed since this function was > > introduced, but nobody seems to have ever used it outside the slab core. > > Besides, this check is racy, so IMO we shouldn't encourage users of the > > API to rely on it. That said, I believe we should drop the return value > > for now. If anybody ever needs it, we can reintroduce it. > > The check is only racy if you have concurrent users. It is not racy if a > subsystem shuts down access to the slabs and then checks if everything is > clean before closing the cache. > > Slab creation and destruction are not serialized. It is the responsibility > of the subsystem to make sure that there are no concurrent users and that > there are no objects remaining before destroying a slab. Right, but I just don't see why a subsystem using a kmem_cache would need to check whether there are any objects left in the cache. I mean, it should somehow keep track of the objects it's allocated anyway, e.g. by linking them in a list. That means it must already have a way to check if it is safe to destroy its cache or not. Suppose we leave the return value as is. A subsystem, right before going to destroy a cache, calls kmem_cache_shrink, which returns 1 (slab is not empty). What is it supposed to do then? Thanks, Vladimir