From: Minchan Kim <minchan@kernel.org>
To: Tejun Heo <tj@kernel.org>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
LKML <linux-kernel@vger.kernel.org>
Subject: Re: [RFC PATCH] kernfs: release kernfs_mutex before the inode allocation
Date: Wed, 17 Nov 2021 17:55:33 -0800 [thread overview]
Message-ID: <YZWylT2SuN+N2Z2K@google.com> (raw)
In-Reply-To: <YZWA+8B1xQOKCMnS@slm.duckdns.org>
On Wed, Nov 17, 2021 at 12:23:55PM -1000, Tejun Heo wrote:
> Hello,
>
> On Wed, Nov 17, 2021 at 02:13:35PM -0800, Minchan Kim wrote:
> > > So, one really low hanging fruit here would be using a separate rwsem per
> > > superblock. Nothing needs synchronization across different users of kernfs
> > > and the locking is shared just because nobody bothered to separate them out
> > > while generalizing it from sysfs.
> >
> > That's really what I wanted but had a question whether we can access
> > superblock from the kernfs_node all the time since there are some
> > functions to access the kernfs_rwsem without ionde, sb context.
> >
> > Is it doable to get the superblock from the kernfs_node all the time?
>
> Ah, right, kernfs_node doesn't point back to kernfs_root. I guess it can go
> one of three ways:
Thanks for the suggestion, Tejun.
I found kernfs_root and it seems like to return kernfs_root from kernfs_node.
If it's true all the case, we would put the rwsem in kernfs_root and change
would be straightforward. Do you see any problem?
>
> a. Follow parent until root kernfs_node and make that guy point to
> kernfs_root through its parent field. This isn't great but the hotter
> paths all have sb / inode already, I think, so if we do this only in the
> really cold paths, it likely isn't too bad.
>
> b. Change the interface so that the callers have to provide kernfs_root. I
> don't think this is gonna be a huge problem. There are a few users of
> kernfs and they always know their roots.
>
> c. Add a field to kernfs_node so that we can always find kernfs_root.
>
> I think b is likely the cheapest && cleanest.
>
> Thanks.
>
> --
> tejun
next prev parent reply other threads:[~2021-11-18 1:55 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-11-16 19:43 [RFC PATCH] kernfs: release kernfs_mutex before the inode allocation Minchan Kim
2021-11-16 19:49 ` Greg Kroah-Hartman
2021-11-16 21:36 ` Minchan Kim
2021-11-17 6:44 ` Greg Kroah-Hartman
2021-11-17 7:27 ` Minchan Kim
2021-11-17 7:39 ` Greg Kroah-Hartman
2021-11-17 21:43 ` Minchan Kim
2021-11-17 21:45 ` Tejun Heo
2021-11-17 22:13 ` Minchan Kim
2021-11-17 22:23 ` Tejun Heo
2021-11-18 1:55 ` Minchan Kim [this message]
2021-11-18 16:35 ` Tejun Heo
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