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SubjectRe: [PATCH v4 3/6] mm: shrinkers: provide shrinkers with names
On Fri, May 27, 2022 at 07:30:34PM +1000, Dave Chinner wrote:
> On Wed, May 25, 2022 at 01:25:57PM -0700, Roman Gushchin wrote:
> > Currently shrinkers are anonymous objects. For debugging purposes they
> > can be identified by count/scan function names, but it's not always
> > useful: e.g. for superblock's shrinkers it's nice to have at least
> > an idea of to which superblock the shrinker belongs.
> >
> > This commit adds names to shrinkers. register_shrinker() and
> > prealloc_shrinker() functions are extended to take a format and
> > arguments to master a name.
> >
> > In some cases it's not possible to determine a good name at the time
> > when a shrinker is allocated. For such cases shrinker_debugfs_rename()
> > is provided.
> >
> > After this change the shrinker debugfs directory looks like:
> > $ cd /sys/kernel/debug/shrinker/
> > $ ls
> > dqcache-16 sb-hugetlbfs-17 sb-rootfs-2 sb-tmpfs-49
> > kfree_rcu-0 sb-hugetlbfs-33 sb-securityfs-6 sb-tracefs-13
> > sb-aio-20 sb-iomem-12 sb-selinuxfs-22 sb-xfs:vda1-36
> > sb-anon_inodefs-15 sb-mqueue-21 sb-sockfs-8 sb-zsmalloc-19
> > sb-bdev-3 sb-nsfs-4 sb-sysfs-26 shadow-18
> > sb-bpf-32 sb-pipefs-14 sb-tmpfs-1 thp_deferred_split-10
> > sb-btrfs:vda2-24 sb-proc-25 sb-tmpfs-27 thp_zero-9
> > sb-cgroup2-30 sb-proc-39 sb-tmpfs-29 xfs_buf-vda1-37
> > sb-configfs-23 sb-proc-41 sb-tmpfs-35 xfs_inodegc-vda1-38
>
> sb-xfs:vda1-36
> xfs_buf-vda1-37
> xfs_inodegc-vda1-38
>
> That's a parsing nightmare right there. Please use the same format
> for everything. You have <subsystem>-<type>:<instance>-<id> for
> superblock stuff, but <subsys>_<type>-<instance>-<id> for the XFS
> stuff. Make it consistent so we aren't reduced to pulling out our
> hair trying to parse this in any useful way:
>
> sb-xfs:vda1-36
> xfs-buf:vda1-37
> xfs-inodegc:vda1-38

Ok, good point, will do in the next version.

>
> FWIW, how we are supposed to know what actually owns these:
>
> sb-tmpfs-1
> sb-tmpfs-27
> sb-tmpfs-29
> sb-tmpfs-35
> sb-tmpfs-49
>
> tmpfs-27 might own all the memory - how do we link that back to a
> mount point, container, user, workload, etc?

I agree, but I've no good idea what to use as an id. We can't put the mount
point, user, group etc together in the file name - it will be too lengthy
(and mount namespaces are making it even more complicated).

Maybe we can add a symlink to the mount point from within the directory?

Do you have any ideas here?

Thanks!

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