From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-ed1-f70.google.com (mail-ed1-f70.google.com [209.85.208.70]) by kanga.kvack.org (Postfix) with ESMTP id 2E1A26B000A for ; Wed, 8 Aug 2018 06:27:40 -0400 (EDT) Received: by mail-ed1-f70.google.com with SMTP id y17-v6so737041eds.22 for ; Wed, 08 Aug 2018 03:27:40 -0700 (PDT) Received: from mx1.suse.de (mx2.suse.de. [195.135.220.15]) by mx.google.com with ESMTPS id f20-v6si3560732edc.98.2018.08.08.03.27.38 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 08 Aug 2018 03:27:38 -0700 (PDT) Date: Wed, 8 Aug 2018 12:27:34 +0200 From: Michal Hocko Subject: Re: [PATCH RFC 01/10] rcu: Make CONFIG_SRCU unconditionally enabled Message-ID: <20180808102734.GH27972@dhcp22.suse.cz> References: <153365347929.19074.12509495712735843805.stgit@localhost.localdomain> <153365625652.19074.8434946780002619802.stgit@localhost.localdomain> <20180808072040.GC27972@dhcp22.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Sender: owner-linux-mm@kvack.org List-ID: To: Kirill Tkhai Cc: akpm@linux-foundation.org, gregkh@linuxfoundation.org, rafael@kernel.org, viro@zeniv.linux.org.uk, darrick.wong@oracle.com, paulmck@linux.vnet.ibm.com, josh@joshtriplett.org, rostedt@goodmis.org, mathieu.desnoyers@efficios.com, jiangshanlai@gmail.com, hughd@google.com, shuah@kernel.org, robh@kernel.org, ulf.hansson@linaro.org, aspriel@gmail.com, vivek.gautam@codeaurora.org, robin.murphy@arm.com, joe@perches.com, heikki.krogerus@linux.intel.com, sfr@canb.auug.org.au, vdavydov.dev@gmail.com, chris@chris-wilson.co.uk, penguin-kernel@I-love.SAKURA.ne.jp, aryabinin@virtuozzo.com, willy@infradead.org, ying.huang@intel.com, shakeelb@google.com, jbacik@fb.com, mingo@kernel.org, mhiramat@kernel.org, linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org [CC Josh - the whole series is http://lkml.kernel.org/r/153365347929.19074.12509495712735843805.stgit@localhost.localdomain] On Wed 08-08-18 13:17:44, Kirill Tkhai wrote: > On 08.08.2018 10:20, Michal Hocko wrote: > > On Tue 07-08-18 18:37:36, Kirill Tkhai wrote: > >> This patch kills all CONFIG_SRCU defines and > >> the code under !CONFIG_SRCU. > > > > The last time somebody tried to do this there was a pushback due to > > kernel tinyfication. So this should really give some numbers about the > > code size increase. Also why can't we make this depend on MMU. Is > > anybody else than the reclaim asking for unconditional SRCU usage? > > I don't know one. The size numbers (sparc64) are: > > $ size image.srcu.disabled > text data bss dec hex filename > 5117546 8030506 1968104 15116156 e6a77c image.srcu.disabled > $ size image.srcu.enabled > text data bss dec hex filename > 5126175 8064346 1968104 15158625 e74d61 image.srcu.enabled > The difference is: 15158625-15116156 = 42469 ~41Kb > > Please, see the measurement details to my answer to Stephen. > > > Btw. I totaly agree with Steven. This is a very poor changelog. It is > > trivial to see what the patch does but it is far from clear why it is > > doing that and why we cannot go other ways. > We possibly can go another way, and there is comment to [2/10] about this. > Percpu rwsem may be used instead, the only thing, it is worse, is it will > make shrink_slab() wait unregistering shrinkers, while srcu-based > implementation does not require this. Well, if unregisterring doesn't do anything subtle - e.g. an allocation or take locks which depend on allocation - and we can guarantee that then blocking shrink_slab shouldn't be a big deal. It is subtle though. Maybe subtle enough to make unconditional SRCU worth it. This all should be in the changelog though. > This may be not a big problem. > But, if SRCU is real problem for embedded people, I really don't want they > hate me in the future because of this, so please CC someone if you know :) I guess Josh was trying to pursue kernel tinification. -- Michal Hocko SUSE Labs