From: Greg Kroah-Hartman <firstname.lastname@example.org> To: Minchan Kim <email@example.com> Cc: Tejun Heo <firstname.lastname@example.org>, LKML <email@example.com> Subject: Re: [RFC PATCH] kernfs: release kernfs_mutex before the inode allocation Date: Wed, 17 Nov 2021 07:44:44 +0100 [thread overview] Message-ID: <YZSk3DECnnknOu5T@kroah.com> (raw) In-Reply-To: <YZQkQcrldGFwqVfirstname.lastname@example.org> On Tue, Nov 16, 2021 at 01:36:01PM -0800, Minchan Kim wrote: > On Tue, Nov 16, 2021 at 08:49:46PM +0100, Greg Kroah-Hartman wrote: > > On Tue, Nov 16, 2021 at 11:43:17AM -0800, Minchan Kim wrote: > > > The kernfs implementation has big lock granularity(kernfs_rwsem) so > > > every kernfs-based(e.g., sysfs, cgroup, dmabuf) fs are able to compete > > > the lock. Thus, if one of userspace goes the sleep under holding > > > the lock for a long time, rest of them should wait it. A example is > > > the holder goes direct reclaim with the lock since it needs memory > > > allocation. Let's fix it at common technique that release the lock > > > and then allocate the memory. Fortunately, kernfs looks like have > > > an refcount so I hope it's fine. > > > > > > Signed-off-by: Minchan Kim <email@example.com> > > > --- > > > fs/kernfs/dir.c | 14 +++++++++++--- > > > fs/kernfs/inode.c | 2 +- > > > fs/kernfs/kernfs-internal.h | 1 + > > > 3 files changed, 13 insertions(+), 4 deletions(-) > > > > What workload hits this lock to cause it to be noticable? > > A app launching since it was dropping the frame since the > latency was too long. How does running a program interact with kernfs filesystems? Which one(s)? > > There was a bunch of recent work in this area to make this much more > > fine-grained, and the theoritical benchmarks that people created (adding > > 10s of thousands of scsi disks at boot time) have gotten better. > > > > But in that work, no one could find a real benchmark or use case that > > anyone could even notice this type of thing. What do you have that > > shows this? > > https://developer.android.com/studio/command-line/perfetto > https://perfetto.dev/docs/data-sources/cpu-scheduling That is links to a tool, not a test we can run ourselves. Or how about the output of that tool? > Android has perfetto tracing system and can show where processes > were stuck. This case was the lock since holder was in direct reclaim > path. Reclaim of what? What is the interaction here with kernfs? Normally this filesystem is not on any "fast paths" that I know of. More specifics would be nice :) thanks, greg k-h
next prev parent reply other threads:[~2021-11-17 6:44 UTC|newest] Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top 2021-11-16 19:43 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 [this message] 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 2021-11-18 16:35 ` Tejun Heo
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