From: Rik van Riel <riel@fb.com>
To: Andrew Morton <akpm@linux-foundation.org>, Tejun Heo <tj@kernel.org>
Cc: "axboe@kernel.dk" <axboe@kernel.dk>,
"jack@suse.cz" <jack@suse.cz>,
"hannes@cmpxchg.org" <hannes@cmpxchg.org>,
"mhocko@kernel.org" <mhocko@kernel.org>,
"vdavydov.dev@gmail.com" <vdavydov.dev@gmail.com>,
"cgroups@vger.kernel.org" <cgroups@vger.kernel.org>,
"linux-mm@kvack.org" <linux-mm@kvack.org>,
"linux-block@vger.kernel.org" <linux-block@vger.kernel.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
Kernel Team <Kernel-team@fb.com>, "Roman Gushchin" <guro@fb.com>
Subject: Re: [PATCH 2/4] bdi: Add bdi->id
Date: Fri, 9 Aug 2019 00:57:24 +0000 [thread overview]
Message-ID: <775309de70c1371e852fa5e6f84ca1ca2727faa0.camel@fb.com> (raw)
In-Reply-To: <20190807120037.72018c136db40e88d89c05d1@linux-foundation.org>
On Wed, 2019-08-07 at 12:00 -0700, Andrew Morton wrote:
> On Wed, 7 Aug 2019 11:31:51 -0700 Tejun Heo <tj@kernel.org> wrote:
>
> > Hello,
> >
> > On Tue, Aug 06, 2019 at 04:01:02PM -0700, Andrew Morton wrote:
> > > On Sat, 3 Aug 2019 07:01:53 -0700 Tejun Heo <tj@kernel.org>
> > > wrote:
> > > > There currently is no way to universally identify and lookup a
> > > > bdi
> > > > without holding a reference and pointer to it. This patch adds
> > > > an
> > > > non-recycling bdi->id and implements bdi_get_by_id() which
> > > > looks up
> > > > bdis by their ids. This will be used by memcg foreign inode
> > > > flushing.
> > >
> > > Why is the id non-recycling? Presumably to address some
> > > lifetime/lookup issues, but what are they?
> >
> > The ID by itself is used to point to the bdi from cgroup and idr
> > recycles really aggressively. Combined with, for example, loop
> > device
> > based containers, stale pointing can become pretty common. We're
> > having similar issues with cgroup IDs.
>
> OK, but why is recycling a problem? For example, file descriptors
> recycle as aggressively as is possible, and that doesn't cause any
> trouble. Presumably recycling is a problem with cgroups because of
> some sort of stale reference problem?
PIDs, on the other hand, we recycle as slowly as
possible...
next prev parent reply other threads:[~2019-08-09 0:57 UTC|newest]
Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-08-03 14:01 [PATCHSET] writeback, memcg: Implement foreign inode flushing Tejun Heo
2019-08-03 14:01 ` [PATCH 1/4] writeback: Generalize and expose wb_completion Tejun Heo
2019-08-15 14:41 ` Jan Kara
2019-08-03 14:01 ` [PATCH 2/4] bdi: Add bdi->id Tejun Heo
2019-08-03 15:39 ` Matthew Wilcox
2019-08-03 15:53 ` Tejun Heo
2019-08-03 16:17 ` Matthew Wilcox
2019-08-06 23:01 ` Andrew Morton
2019-08-07 18:31 ` Tejun Heo
2019-08-07 19:00 ` Andrew Morton
2019-08-07 20:34 ` Tejun Heo
2019-08-09 0:57 ` Rik van Riel [this message]
2019-08-15 14:46 ` Jan Kara
2019-08-15 17:34 ` Tejun Heo
2019-08-03 14:01 ` [PATCH 3/4] writeback, memcg: Implement cgroup_writeback_by_id() Tejun Heo
2019-08-15 14:05 ` Jan Kara
2019-08-15 15:43 ` Tejun Heo
2019-08-15 14:54 ` Jan Kara
2019-08-15 16:12 ` Tejun Heo
2019-08-03 14:01 ` [PATCH 4/4] writeback, memcg: Implement foreign dirty flushing Tejun Heo
2019-08-06 23:03 ` Andrew Morton
2019-08-07 18:34 ` Tejun Heo
2019-08-15 14:34 ` Jan Kara
2019-08-15 17:31 ` Tejun Heo
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