tools/cgroup: add memcg_slabinfo.py tool

Add a drgn-based tool to display slab information for a given memcg. Can
replace cgroup v1 memory.kmem.slabinfo interface on cgroup v2, but in a
more flexiable way.

Currently supports only SLUB configuration, but SLAB can be trivially
added later.

Output example:
$ sudo ./tools/cgroup/memcg_slabinfo.py /sys/fs/cgroup/user.slice/user-111017.slice/user\@111017.service
shmem_inode_cache 92 92 704 46 8 : tunables 0 0 0 : slabdata 2 2 0
eventpoll_pwq 56 56 72 56 1 : tunables 0 0 0 : slabdata 1 1 0
eventpoll_epi 32 32 128 32 1 : tunables 0 0 0 : slabdata 1 1 0
kmalloc-8 0 0 8 512 1 : tunables 0 0 0 : slabdata 0 0 0
kmalloc-96 0 0 96 42 1 : tunables 0 0 0 : slabdata 0 0 0
kmalloc-2048 0 0 2048 16 8 : tunables 0 0 0 : slabdata 0 0 0
kmalloc-64 128 128 64 64 1 : tunables 0 0 0 : slabdata 2 2 0
mm_struct 160 160 1024 32 8 : tunables 0 0 0 : slabdata 5 5 0
signal_cache 96 96 1024 32 8 : tunables 0 0 0 : slabdata 3 3 0
sighand_cache 45 45 2112 15 8 : tunables 0 0 0 : slabdata 3 3 0
files_cache 138 138 704 46 8 : tunables 0 0 0 : slabdata 3 3 0
task_delay_info 153 153 80 51 1 : tunables 0 0 0 : slabdata 3 3 0
task_struct 27 27 3520 9 8 : tunables 0 0 0 : slabdata 3 3 0
radix_tree_node 56 56 584 28 4 : tunables 0 0 0 : slabdata 2 2 0
btrfs_inode 140 140 1136 28 8 : tunables 0 0 0 : slabdata 5 5 0
kmalloc-1024 64 64 1024 32 8 : tunables 0 0 0 : slabdata 2 2 0
kmalloc-192 84 84 192 42 2 : tunables 0 0 0 : slabdata 2 2 0
inode_cache 54 54 600 27 4 : tunables 0 0 0 : slabdata 2 2 0
kmalloc-128 0 0 128 32 1 : tunables 0 0 0 : slabdata 0 0 0
kmalloc-512 32 32 512 32 4 : tunables 0 0 0 : slabdata 1 1 0
skbuff_head_cache 32 32 256 32 2 : tunables 0 0 0 : slabdata 1 1 0
sock_inode_cache 46 46 704 46 8 : tunables 0 0 0 : slabdata 1 1 0
cred_jar 378 378 192 42 2 : tunables 0 0 0 : slabdata 9 9 0
proc_inode_cache 96 96 672 24 4 : tunables 0 0 0 : slabdata 4 4 0
dentry 336 336 192 42 2 : tunables 0 0 0 : slabdata 8 8 0
filp 697 864 256 32 2 : tunables 0 0 0 : slabdata 27 27 0
anon_vma 644 644 88 46 1 : tunables 0 0 0 : slabdata 14 14 0
pid 1408 1408 64 64 1 : tunables 0 0 0 : slabdata 22 22 0
vm_area_struct 1200 1200 200 40 2 : tunables 0 0 0 : slabdata 30 30 0

Signed-off-by: Roman Gushchin <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Acked-by: Tejun Heo <[e-mail]>
Cc: Christoph Lameter <[e-mail]>
Cc: Johannes Weiner <[e-mail]>
Cc: Michal Hocko <[e-mail]>
Cc: Shakeel Butt <[e-mail]>
Cc: Vlastimil Babka <[e-mail]>
Link: http://lkml.kernel.org/r/[e-mail]
Signed-off-by: Linus Torvalds <[e-mail]>

tools/cgroup/memcg_slabinfo.py

···
+#!/usr/bin/env drgn
+#
+# Copyright (C) 2020 Roman Gushchin <[e-mail]>
+# Copyright (C) 2020 Facebook
+
+from os import stat
+import argparse
+import sys
+
+from drgn.helpers.linux import list_for_each_entry, list_empty
+from drgn.helpers.linux import for_each_page
+from drgn.helpers.linux.cpumask import for_each_online_cpu
+from drgn.helpers.linux.percpu import per_cpu_ptr
+from drgn import container_of, FaultError, Object
+
+
+DESC = """
+This is a drgn script to provide slab statistics for memory cgroups.
+It supports cgroup v2 and v1 and can emulate memory.kmem.slabinfo
+interface of cgroup v1.
+For drgn, visit https://github.com/osandov/drgn.
+"""
+
+
+MEMCGS = {}
+
+OO_SHIFT = 16
+OO_MASK = ((1 << OO_SHIFT) - 1)
+
+
+def err(s):
+    print('slabinfo.py: error: %s' % s, file=sys.stderr, flush=True)
+    sys.exit(1)
+
+
+def find_memcg_ids(css=prog['root_mem_cgroup'].css, prefix=''):
+    if not list_empty(css.children.address_of_()):
+        for css in list_for_each_entry('struct cgroup_subsys_state',
+                                       css.children.address_of_(),
+                                       'sibling'):
+            name = prefix + '/' + css.cgroup.kn.name.string_().decode('utf-8')
+            memcg = container_of(css, 'struct mem_cgroup', 'css')
+            MEMCGS[css.cgroup.kn.id.value_()] = memcg
+            find_memcg_ids(css, name)
+
+
+def is_root_cache(s):
+    try:
+        return False if s.memcg_params.root_cache else True
+    except AttributeError:
+        return True
+
+
+def cache_name(s):
+    if is_root_cache(s):
+        return s.name.string_().decode('utf-8')
+    else:
+        return s.memcg_params.root_cache.name.string_().decode('utf-8')
+
+
+# SLUB
+
+def oo_order(s):
+    return s.oo.x >> OO_SHIFT
+
+
+def oo_objects(s):
+    return s.oo.x & OO_MASK
+
+
+def count_partial(n, fn):
+    nr_pages = 0
+    for page in list_for_each_entry('struct page', n.partial.address_of_(),
+                                    'lru'):
+         nr_pages += fn(page)
+    return nr_pages
+
+
+def count_free(page):
+    return page.objects - page.inuse
+
+
+def slub_get_slabinfo(s, cfg):
+    nr_slabs = 0
+    nr_objs = 0
+    nr_free = 0
+
+    for node in range(cfg['nr_nodes']):
+        n = s.node[node]
+        nr_slabs += n.nr_slabs.counter.value_()
+        nr_objs += n.total_objects.counter.value_()
+        nr_free += count_partial(n, count_free)
+
+    return {'active_objs': nr_objs - nr_free,
+            'num_objs': nr_objs,
+            'active_slabs': nr_slabs,
+            'num_slabs': nr_slabs,
+            'objects_per_slab': oo_objects(s),
+            'cache_order': oo_order(s),
+            'limit': 0,
+            'batchcount': 0,
+            'shared': 0,
+            'shared_avail': 0}
+
+
+def cache_show(s, cfg, objs):
+    if cfg['allocator'] == 'SLUB':
+        sinfo = slub_get_slabinfo(s, cfg)
+    else:
+        err('SLAB isn\'t supported yet')
+
+    if cfg['shared_slab_pages']:
+        sinfo['active_objs'] = objs
+        sinfo['num_objs'] = objs
+
+    print('%-17s %6lu %6lu %6u %4u %4d'
+          ' : tunables %4u %4u %4u'
+          ' : slabdata %6lu %6lu %6lu' % (
+              cache_name(s), sinfo['active_objs'], sinfo['num_objs'],
+              s.size, sinfo['objects_per_slab'], 1 << sinfo['cache_order'],
+              sinfo['limit'], sinfo['batchcount'], sinfo['shared'],
+              sinfo['active_slabs'], sinfo['num_slabs'],
+              sinfo['shared_avail']))
+
+
+def detect_kernel_config():
+    cfg = {}
+
+    cfg['nr_nodes'] = prog['nr_online_nodes'].value_()
+
+    if prog.type('struct kmem_cache').members[1][1] == 'flags':
+        cfg['allocator'] = 'SLUB'
+    elif prog.type('struct kmem_cache').members[1][1] == 'batchcount':
+        cfg['allocator'] = 'SLAB'
+    else:
+        err('Can\'t determine the slab allocator')
+
+    cfg['shared_slab_pages'] = False
+    try:
+        if prog.type('struct obj_cgroup'):
+            cfg['shared_slab_pages'] = True
+    except:
+        pass
+
+    return cfg
+
+
+def for_each_slab_page(prog):
+    PGSlab = 1 << prog.constant('PG_slab')
+    PGHead = 1 << prog.constant('PG_head')
+
+    for page in for_each_page(prog):
+        try:
+            if page.flags.value_() & PGSlab:
+                yield page
+        except FaultError:
+            pass
+
+
+def main():
+    parser = argparse.ArgumentParser(description=DESC,
+                                     formatter_class=
+                                     argparse.RawTextHelpFormatter)
+    parser.add_argument('cgroup', metavar='CGROUP',
+                        help='Target memory cgroup')
+    args = parser.parse_args()
+
+    try:
+        cgroup_id = stat(args.cgroup).st_ino
+        find_memcg_ids()
+        memcg = MEMCGS[cgroup_id]
+    except KeyError:
+        err('Can\'t find the memory cgroup')
+
+    cfg = detect_kernel_config()
+
+    print('# name            <active_objs> <num_objs> <objsize> <objperslab> <pagesperslab>'
+          ' : tunables <limit> <batchcount> <sharedfactor>'
+          ' : slabdata <active_slabs> <num_slabs> <sharedavail>')
+
+    if cfg['shared_slab_pages']:
+        obj_cgroups = set()
+        stats = {}
+        caches = {}
+
+        # find memcg pointers belonging to the specified cgroup
+        obj_cgroups.add(memcg.objcg.value_())
+        for ptr in list_for_each_entry('struct obj_cgroup',
+                                       memcg.objcg_list.address_of_(),
+                                       'list'):
+            obj_cgroups.add(ptr.value_())
+
+        # look over all slab pages, belonging to non-root memcgs
+        # and look for objects belonging to the given memory cgroup
+        for page in for_each_slab_page(prog):
+            objcg_vec_raw = page.obj_cgroups.value_()
+            if objcg_vec_raw == 0:
+                continue
+            cache = page.slab_cache
+            if not cache:
+                continue
+            addr = cache.value_()
+            caches[addr] = cache
+            # clear the lowest bit to get the true obj_cgroups
+            objcg_vec = Object(prog, page.obj_cgroups.type_,
+                               value=objcg_vec_raw & ~1)
+
+            if addr not in stats:
+                stats[addr] = 0
+
+            for i in range(oo_objects(cache)):
+                if objcg_vec[i].value_() in obj_cgroups:
+                    stats[addr] += 1
+
+        for addr in caches:
+            if stats[addr] > 0:
+                cache_show(caches[addr], cfg, stats[addr])
+
+    else:
+        for s in list_for_each_entry('struct kmem_cache',
+                                     memcg.kmem_caches.address_of_(),
+                                     'memcg_params.kmem_caches_node'):
+            cache_show(s, cfg, None)
+
+
+main()