Messages in this thread | | | Date | Tue, 16 Nov 2021 13:36:01 -0800 | From | Minchan Kim <> | Subject | Re: [RFC PATCH] kernfs: release kernfs_mutex before the inode allocation |
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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 <minchan@kernel.org> > > --- > > 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.
> > 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
Android has perfetto tracing system and can show where processes were stuck. This case was the lock since holder was in direct reclaim path.
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