From mboxrd@z Thu Jan 1 00:00:00 1970 From: Johannes Weiner Subject: Re: [PATCH] mm: memcontrol: Cast mismatched enum types passed to memcg state and event functions Date: Thu, 27 Jul 2017 10:17:42 -0400 Message-ID: <20170727141742.GA19738@cmpxchg.org> References: <20170726192356.18420-1-mka@chromium.org> <20170726142309.ac40faf5eb99568e6edb064c@linux-foundation.org> <20170726214914.GA84665@google.com> <20170726150332.313e48837d97046924ddaa16@linux-foundation.org> <20170727072451.GH20970@dhcp22.suse.cz> Mime-Version: 1.0 Return-path: DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=cmpxchg.org ; s=x; h=In-Reply-To:Content-Type:MIME-Version:References:Message-ID:Subject: Cc:To:From:Date:Sender:Reply-To:Content-Transfer-Encoding:Content-ID: Content-Description:Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc :Resent-Message-ID:List-Id:List-Help:List-Unsubscribe:List-Subscribe: List-Post:List-Owner:List-Archive; bh=SG6ngti6aMaaEmYz1BFsCSq+u+qeRiXhPYrHnjziGTA=; b=UUqBxAV/cDzKFL8zf8CNe8uM2d IM8zG36vTYoueiECJ/eZoVOM9SgHmp5Q9UsqNRZ7Yeys4iB3+HhZpz1LbGb4jihIkHdX4L69ZfvRs l8e+ph7QAcb/QYBMk1DnekQqGhXqwvsU2ErI4jk5OPagy5qA22ZBBnN3Ery3sSV2vFkw=; Content-Disposition: inline In-Reply-To: <20170727072451.GH20970-2MMpYkNvuYDjFM9bn6wA6Q@public.gmane.org> Sender: cgroups-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org List-ID: Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: Michal Hocko Cc: Andrew Morton , Matthias Kaehlcke , Vladimir Davydov , linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, cgroups-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-mm-Bw31MaZKKs3YtjvyW6yDsg@public.gmane.org, Doug Anderson On Thu, Jul 27, 2017 at 09:24:51AM +0200, Michal Hocko wrote: > On Wed 26-07-17 15:03:32, Andrew Morton wrote: > > On Wed, 26 Jul 2017 14:49:14 -0700 Matthias Kaehlcke wrote: > > > > > El Wed, Jul 26, 2017 at 02:23:09PM -0700 Andrew Morton ha dit: > > > > > > > On Wed, 26 Jul 2017 12:23:56 -0700 Matthias Kaehlcke wrote: > > > > > > > > > In multiple instances enum values of an incorrect type are passed to > > > > > mod_memcg_state() and other memcg functions. Apparently this is > > > > > intentional, however clang rightfully generates tons of warnings about > > > > > the mismatched types. Cast the offending values to the type expected > > > > > by the called function. The casts add noise, but this seems preferable > > > > > over losing the typesafe interface or/and disabling the warning. > > > > > > > > > > ... > > > > > > > > > > --- a/include/linux/memcontrol.h > > > > > +++ b/include/linux/memcontrol.h > > > > > @@ -576,7 +576,7 @@ static inline void __mod_lruvec_state(struct lruvec *lruvec, > > > > > if (mem_cgroup_disabled()) > > > > > return; > > > > > pn = container_of(lruvec, struct mem_cgroup_per_node, lruvec); > > > > > - __mod_memcg_state(pn->memcg, idx, val); > > > > > + __mod_memcg_state(pn->memcg, (enum memcg_stat_item)idx, val); > > > > > __this_cpu_add(pn->lruvec_stat->count[idx], val); > > > > > } > > > > > > > > __mod_memcg_state()'s `idx' arg can be either enum memcg_stat_item or > > > > enum memcg_stat_item. I think it would be better to just admit to > > > > ourselves that __mod_memcg_state() is more general than it appears, and > > > > change it to take `int idx'. I assume that this implicit cast of an > > > > enum to an int will not trigger a clang warning? > > > > > > Sure, no warnings are raised for implicit casts from enum to > > > int. > > > > > > __mod_memcg_state() is not the only function though, all these > > > functions are called with conflicting types: > > > > > > memcg_page_state() > > > __mod_memcg_state() > > > mod_memcg_state() > > > count_memcg_events() > > > count_memcg_page_event() > > > memcg_sum_events() > > > > > > Should we change all of them to reveice an int instead of an enum? > > > > I suspect so - the current implementation is denying reality and your > > original proposal is a bit of a fudge. But I'll await input from the > > memcg peeps. > > well, those enums do not help type safety much I am afraid so turining > the idx to int sounds like a more preferable way to me. Johannes? I agree, turning the parameter into an int makes for much nicer code than the casts. Matthias, would you care to update your patch to change these over?