From: Tejun Heo <tj@kernel.org>
To: Michal Hocko <mhocko@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 09:45:10 -0800 [thread overview]
Message-ID: <20191115174510.GQ4163745@devbig004.ftw2.facebook.com> (raw)
In-Reply-To: <20191115174031.GA15216@dhcp22.suse.cz>
On Fri, Nov 15, 2019 at 06:40:31PM +0100, Michal Hocko wrote:
> I am sorry but I do not follow. How can css_tryget_online provide the
> same semantic when the css can go offline right after the tryget call
> returns so it is effectivelly undistinguishable from the case when the
> css was already online before the call was made. Or is my understanding
> of what Roman's said earlier in the thread?
It's *exactly* the same semantics as opening a file and deleting it
and keeping using it vs. deleting a file and then trying to open it.
You can't give out a new reference when the entity's visibility is
expected to be gone already and that's the exactly the condition that
tryget_online avoids. I don't know how to better explain it if the
file analogy doesn't work.
Thanks.
--
tejun
next prev parent reply other threads:[~2019-11-15 17:45 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 [this message]
2019-11-15 17:47 ` Michal Hocko
2019-11-15 17:48 ` Tejun Heo
2019-11-15 18:03 ` Michal Hocko
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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