Re: [PATCH 00/10] shrinker debugging, .to_text() report (resend)

[Kent Overstreet <kent.overstreet@linux.dev>]

On Wed, Aug 28, 2024 at 11:51:34AM GMT, Dave Chinner wrote:
> On Sat, Aug 24, 2024 at 03:10:07PM -0400, Kent Overstreet wrote:
> > recently new OOMs have been cropping up, and reclaim is implicated, so
> > I've had to dust off these patches.
> > 
> > nothing significant has changed since the last time I posted, and they
> > have been valuable - Dave, think we can get them in?
> 
> You need to describe what this does. What does the output look like?
> Where does it go (console, dmesg, etc). When is it called, etc.
> Links to previous review threads so people can get back up to speed
> on what was discussed last time and determine whether issues raised
> were solved. A changelog since the last posting is helpful, too...

Not much has changed since last posting, besides tweaking/improving
counters...

objects, requested to free, objects freed: so we can tell if a shrinker
isn't freeing as requested

last scanned and last freed are new - so we can tell if a shrinker's
gotten stuck (perhaps it requires a lock that it isn't able to get)

bcachefs shrinkers additionally have counters for every distinct reason
an object wasn't freed - this has been quite useful in the past:

BTW - the next thing I want to get done is adding an interface for
shrinkers to report the amount of memory they own in bytes. This will
greatly aid the show_mem report, so it can skip reporting on shrinkers
entirely if they don't control much memory or pick a number to show more
intelligently.

It'll also let us finally fix the free command.

root@moria-kvm:/sys/kernel/debug/shrinker$ cat 05baba83-05ef-4d71-be0e-121bdabfee36-btree_key_cache-43/report 
05baba83-05ef-4d71-be0e-121bdabfee36-btree_key_cache
objects:             122411
requested to free:   63
objects freed:       0
last scanned:        198 sec ago
last freed:          42949578 sec ago
ns per object freed: 0
keys:                         129119
dirty:                          6580
table size:                   262144

shrinker:
requested_to_free:                 0
freed:                             0
skipped_dirty:                    21
skipped_accessed:                 42
skipped_lock_fail:                 0

pending:                      114727

root@moria-kvm:/sys/kernel/debug/shrinker# cat sb-bcachefs-44/report 
sb-bcachefs
objects:             1
requested to free:   0
objects freed:       0
last scanned:        42949693 sec ago
last freed:          42949693 sec ago
ns per object freed: 0
inodes:   total 2 shrinkable 0
dentries: toal 2 shrinkbale 1