From: Matthew Wilcox <willy@infradead.org>
To: Tejun Heo <tj@kernel.org>
Cc: axboe@kernel.dk, jack@suse.cz, hannes@cmpxchg.org,
mhocko@kernel.org, vdavydov.dev@gmail.com,
cgroups@vger.kernel.org, linux-mm@kvack.org,
linux-block@vger.kernel.org, linux-kernel@vger.kernel.org,
kernel-team@fb.com, guro@fb.com, akpm@linux-foundation.org
Subject: Re: [PATCH 2/4] bdi: Add bdi->id
Date: Sat, 3 Aug 2019 09:17:43 -0700 [thread overview]
Message-ID: <20190803161743.GB932@bombadil.infradead.org> (raw)
In-Reply-To: <20190803155349.GD136335@devbig004.ftw2.facebook.com>
On Sat, Aug 03, 2019 at 08:53:49AM -0700, Tejun Heo wrote:
> Hey, Matthew.
>
> On Sat, Aug 03, 2019 at 08:39:08AM -0700, Matthew Wilcox wrote:
> > On Sat, Aug 03, 2019 at 07:01:53AM -0700, Tejun Heo 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.
> > >
> > > I left bdi_list alone for simplicity and because while rb_tree does
> > > support rcu assignment it doesn't seem to guarantee lossless walk when
> > > walk is racing aginst tree rebalance operations.
> >
> > This would seem like the perfect use for an allocating xarray. That
> > does guarantee lossless walk under the RCU lock. You could get rid of the
> > bdi_list too.
>
> It definitely came to mind but there's a bunch of downsides to
> recycling IDs or using radix tree for non-compacting allocations.
Ah, I wasn't sure what would happen if you recycled an ID. I agree, the
radix tree is pretty horrid for monotonically increasing IDs. I'm still
working on the maple tree to replace it, but that's going slower than
I would like, so I can't in good conscience ask you to wait for it to
be ready.
next prev parent reply other threads:[~2019-08-03 16:17 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 [this message]
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
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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