From: Michal Hocko <mhocko@kernel.org>
To: Tejun Heo <tj@kernel.org>
Cc: "Roman Gushchin" <guro@fb.com>,
"Michal Koutný" <mkoutny@suse.com>,
"linux-mm@kvack.org" <linux-mm@kvack.org>,
"Andrew Morton" <akpm@linux-foundation.org>,
"Johannes Weiner" <hannes@cmpxchg.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"Kernel Team" <Kernel-team@fb.com>,
"stable@vger.kernel.org" <stable@vger.kernel.org>
Subject: Re: [PATCH 1/2] mm: memcg: switch to css_tryget() in get_mem_cgroup_from_mm()
Date: Fri, 15 Nov 2019 19:03:03 +0100 [thread overview]
Message-ID: <20191115180303.GC15216@dhcp22.suse.cz> (raw)
In-Reply-To: <20191115174844.GR4163745@devbig004.ftw2.facebook.com>
On Fri 15-11-19 09:48:44, Tejun Heo wrote:
> On Fri, Nov 15, 2019 at 06:47:21PM +0100, Michal Hocko wrote:
> > s@online@offline@
> >
> > And reading after myself it turned out to sound differently than I
> > meant. What I wanted to say really is, what is the difference that
> > css_tryget_online really guarantee when the css might go offline right
> > after the call suceeds so more specifically what is the difference
> > between
> > if (css_tryget()) {
> > if (online)
> > DO_SOMETHING
> > }
> > and
> > if (css_tryget_online()) {
> > DO_SOMETHING
> > }
> >
> > both of them are racy and do not provide any guarantee wrt. online
> > state.
>
> It's about not giving new reference when the object is known to be
> delted to the user.
This part is clear to me. The failure just says it is already too late
to do anything. I just still struggle why the success is telling me much
more when the state might change before I can do anything on the object.
I could see a usefulness if I've had a guarantee that the object stays
online while I hold a $FOO lock but if there is nothing like that then
we are just having already too late or potentially too late.
Anyway it's been a hard week and the brain is just going for the weekend
so I just might be dense now.
> Can you please think more about how file deletions work?
I will try that with a fresh brain next week.
--
Michal Hocko
SUSE Labs
next prev parent reply other threads:[~2019-11-15 18:03 UTC|newest]
Thread overview: 34+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-11-06 22:51 [PATCH 1/2] mm: memcg: switch to css_tryget() in get_mem_cgroup_from_mm() Roman Gushchin
2019-11-06 22:51 ` [PATCH 2/2] mm: hugetlb: switch to css_tryget() in hugetlb_cgroup_charge_cgroup() Roman Gushchin
2019-11-07 0:26 ` Johannes Weiner
2019-11-07 2:31 ` Shakeel Butt
2019-11-07 15:44 ` Tejun Heo
2019-11-07 0:22 ` [PATCH 1/2] mm: memcg: switch to css_tryget() in get_mem_cgroup_from_mm() Johannes Weiner
2019-11-07 1:25 ` Shakeel Butt
2019-11-07 1:43 ` Johannes Weiner
2019-11-07 1:43 ` Roman Gushchin
2019-11-07 2:21 ` Shakeel Butt
2019-11-07 2:28 ` Shakeel Butt
2019-11-07 12:21 ` Michal Hocko
2019-11-07 15:43 ` Tejun Heo
2019-11-07 16:42 ` Roman Gushchin
2019-11-07 17:02 ` Michal Hocko
2019-11-07 22:41 ` Roman Gushchin
2019-11-08 8:53 ` Michal Hocko
2019-11-07 15:43 ` Tejun Heo
2019-11-13 16:29 ` Michal Koutný
2019-11-13 17:08 ` Roman Gushchin
2019-11-14 19:16 ` Michal Hocko
2019-11-14 19:20 ` Tejun Heo
2019-11-14 19:33 ` Michal Hocko
2019-11-14 19:37 ` Tejun Heo
2019-11-15 17:40 ` Michal Hocko
2019-11-15 17:45 ` Tejun Heo
2019-11-15 17:47 ` Michal Hocko
2019-11-15 17:48 ` Tejun Heo
2019-11-15 18:03 ` Michal Hocko [this message]
2019-11-15 18:07 ` Roman Gushchin
2019-11-18 9:43 ` Michal Hocko
2019-11-15 18:13 ` Roman Gushchin
2019-11-21 15:28 ` Michal Koutný
2019-11-22 8:20 ` Michal Hocko
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