From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-ua0-f199.google.com (mail-ua0-f199.google.com [209.85.217.199]) by kanga.kvack.org (Postfix) with ESMTP id 934286B0005 for ; Wed, 8 Aug 2018 19:02:43 -0400 (EDT) Received: by mail-ua0-f199.google.com with SMTP id k5-v6so3072541ual.10 for ; Wed, 08 Aug 2018 16:02:43 -0700 (PDT) Received: from mail-sor-f65.google.com (mail-sor-f65.google.com. [209.85.220.65]) by mx.google.com with SMTPS id q2-v6sor1856069vkq.228.2018.08.08.16.02.42 for (Google Transport Security); Wed, 08 Aug 2018 16:02:42 -0700 (PDT) MIME-Version: 1.0 References: <153365347929.19074.12509495712735843805.stgit@localhost.localdomain> <153365625652.19074.8434946780002619802.stgit@localhost.localdomain> <20180808072040.GC27972@dhcp22.suse.cz> <20180808161330.GA22863@localhost> <20180808180152.GA2480@localhost> In-Reply-To: <20180808180152.GA2480@localhost> From: Shakeel Butt Date: Wed, 8 Aug 2018 16:02:29 -0700 Message-ID: Subject: Re: [PATCH RFC 01/10] rcu: Make CONFIG_SRCU unconditionally enabled Content-Type: text/plain; charset="UTF-8" Sender: owner-linux-mm@kvack.org List-ID: To: josh@joshtriplett.org Cc: Kirill Tkhai , Michal Hocko , Andrew Morton , gregkh@linuxfoundation.org, rafael@kernel.org, Alexander Viro , "Darrick J. Wong" , Paul McKenney , Steven Rostedt , mathieu.desnoyers@efficios.com, jiangshanlai@gmail.com, Hugh Dickins , 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, Stephen Rothwell , Vladimir Davydov , Chris Wilson , Tetsuo Handa , Andrey Ryabinin , Matthew Wilcox , Huang Ying , jbacik@fb.com, Ingo Molnar , mhiramat@kernel.org, LKML , linux-fsdevel , Linux MM On Wed, Aug 8, 2018 at 11:02 AM Josh Triplett wrote: > > On Wed, Aug 08, 2018 at 07:30:13PM +0300, Kirill Tkhai wrote: > > On 08.08.2018 19:23, Kirill Tkhai wrote: > > > On 08.08.2018 19:13, Josh Triplett wrote: > > >> On Wed, Aug 08, 2018 at 01:17:44PM +0300, 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 > > >> > > >> 41k is a *substantial* size increase. However, can you compare > > >> tinyconfig with and without this patch? That may have a smaller change. > > > > > > $ size image.srcu.disabled > > > text data bss dec hex filename > > > 1105900 195456 63232 1364588 14d26c image.srcu.disabled > > > > > > $ size image.srcu.enabled > > > text data bss dec hex filename > > > 1106960 195528 63232 1365720 14d6d8 image.srcu.enabled > > > > > > 1365720-1364588 = 1132 ~ 1Kb > > > > 1Kb is not huge size. It looks as not a big price for writing generic code > > for only case (now some places have CONFIG_SRCU and !CONFIG_SRCU variants, > > e.g. drivers/base/core.c). What do you think? > > That's a little more reasonable than 41k, likely because of > CONFIG_TINY_SRCU. That's still not ideal, though. And as far as I can > tell, the *only* two pieces of core code that use SRCU are > drivers/base/core.c and kernel/notifier.c, and the latter is exclusively > code to use notifiers with SRCU, not notifiers wanting to use SRCU > themselves. So, as far as I can tell, this would really just save a > couple of small #ifdef sections in drivers/base/core.c, and I think > those #ifdef sections could be simplified even further. That doesn't > seem worth it at all. Hi Josh, the motivation behind enabling SRCU is not to simplify the code in drivers/base/core.c but rather not to introduce similar ifdefs in mm/vmscan.c for shrinker traversals. Shakeel