kernfs,memcg: Add helpers to get memcg info

Add kernfs based helpers to extract memcg related information,
like number of active and inactive memcgroups, page cache pages
pinning memcgroups etc.

Orabug: 37322867
Signed-off-by: Imran Khan <[email protected]>

drgn_tools/kernfs_memcg.py

@@ -0,0 +1,251 @@
+# Copyright (c) 2024, Oracle and/or its affiliates.
+# Licensed under the Universal Permissive License v 1.0 as shown at https://oss.oracle.com/licenses/upl/
+"""
+Kernfs_memcg
+--------------
+
+The ``drgn.helpers.linux.kernfs_memcg`` module provides helpers for working with the
+Linux memcg subsystem.
+"""
+import argparse
+from typing import Iterator
+
+from drgn import cast
+from drgn import container_of
+from drgn import FaultError
+from drgn import Object
+from drgn import Program
+from drgn.helpers.common.format import decode_enum_type_flags
+from drgn.helpers.linux import cgroup_path
+from drgn.helpers.linux import css_for_each_descendant_pre
+from drgn.helpers.linux import find_slab_cache
+from drgn.helpers.linux import for_each_page
+from drgn.helpers.linux import inode_path
+from drgn.helpers.linux import kernfs_path
+from drgn.helpers.linux import PageSlab
+from drgn.helpers.linux import slab_cache_for_each_allocated_object
+from drgn.helpers.linux import slab_cache_is_merged
+
+from drgn_tools.corelens import CorelensModule
+from drgn_tools.dentry import dentry_path_any_mount
+
+
+_KERNFS_TYPE_MASK = 0xF
+# cgroup subsystem id for memory cgroup, from kernel/cgroup/cgroup.c
+_MEMORY_CGRP_ID = 4
+
+
+def decode_css_flags(css: Object) -> str:
+    """
+    Get a human-readable representation of cgroup_subsys_state.flags
+
+    :param css: ``struct cgroup_subsys_state *``
+    """
+    CSS_DYING = css.prog_["CSS_DYING"]
+    flags = css.flags.value_()
+    if not flags:
+        # There is no dedicated flag value to indicate a zombie cgroup.
+        # A css.flags value of 0 indicates that cgroup destruction is
+        # complete but cgroup object has not been fully freed because
+        # of being pinned by some other object
+        return "ZOMBIE"
+
+    return decode_enum_type_flags(flags, CSS_DYING.type_, False)
+
+
+def for_each_kernfs_node(prog: Program) -> Iterator[Object]:
+    """
+    Iterate over all kernfs_node objects in the system.
+
+    :returns: Iterator of ``struct kernfs_node *`` objects.
+    """
+    kernfs_node_cache = find_slab_cache(prog, "kernfs_node_cache")
+    if not slab_cache_is_merged(kernfs_node_cache):
+        for kn in slab_cache_for_each_allocated_object(
+            kernfs_node_cache, "struct kernfs_node"
+        ):
+            yield kn
+    else:
+        print(
+            "Can't iterate through kernfs_node_cache, because its merged with other slab-cache(s)"
+        )
+
+
+def dump_memcgroup_hierarchy(prog: Program) -> None:
+    """
+    Dump hierarchy of active mem cgroups.
+    """
+    cgroup_subsys = prog["cgroup_subsys"][_MEMORY_CGRP_ID]
+    css = cgroup_subsys.root.cgrp.self.address_of_()
+    print(f"dumping: {cgroup_subsys.name.string_().decode()} hierarchy")
+    for pos in css_for_each_descendant_pre(css):
+        cgroup_state = decode_css_flags(pos)
+        print(
+            f"path: {cgroup_path(pos.cgroup).decode()} state: {cgroup_state}"
+        )
+
+
+def kernfs_node_of_cgroup(kn: Object) -> bool:
+    """
+    Check if a kernfs_node object represents a cgroup object.
+
+    :param kn: ``struct kernfs_node *``
+    :returns: True if kernfs_node object represents a cgroup object,
+              False otherwise.
+    """
+    if (kn.flags.value_() & _KERNFS_TYPE_MASK) == kn.prog_.constant(
+        "KERNFS_DIR"
+    ).value_():
+        try:
+            cgrp = cast("struct cgroup *", kn.priv)
+            return cgrp.kn == kn
+        except FaultError:
+            return False
+    else:
+        return False
+
+
+def kernfs_node_of_memcgroup(kn: Object) -> bool:
+    """
+    Check if a kernfs_node object represents a mem cgroup object.
+
+    :param kn: ``struct kernfs_node *``
+    :returns: True if kernfs_node object represents a mem cgroup object,
+              False otherwise.
+    """
+    if kernfs_node_of_cgroup(kn):
+        prog = kn.prog_
+        cgrp = cast("struct cgroup *", kn.priv)
+        return prog["cgroup_subsys"][_MEMORY_CGRP_ID].root == cgrp.root
+    else:
+        return False
+
+
+def dump_memcg_kernfs_nodes(prog: Program) -> None:
+    """
+    List all kernfs_node objects that represent a mem cgroup.
+    """
+    count = 0
+    for kn in for_each_kernfs_node(prog):
+        if kernfs_node_of_memcgroup(kn):
+            count = count + 1
+            path = kernfs_path(kn).decode()
+            print("kernfs_node: ", hex(kn.value_()), "  ", path)
+
+    print("Total number of memcg kernfs_node objects: ", count)
+
+
+def get_num_active_mem_cgroups(prog: Program) -> int:
+    """
+    Get number of active mem cgroups.
+    """
+    mem_cgroup_subsys = prog["cgroup_subsys"][_MEMORY_CGRP_ID]
+    # add 1 to number of active memcgroups to account for root memcgroup
+    return mem_cgroup_subsys.root.cgrp.nr_descendants.value_() + 1
+
+
+def get_num_dying_mem_cgroups(prog: Program) -> int:
+    """
+    Get number of inactive or dying mem cgroups.
+    """
+    mem_cgroup_subsys = prog["cgroup_subsys"][_MEMORY_CGRP_ID]
+    return mem_cgroup_subsys.root.cgrp.nr_dying_descendants.value_()
+
+
+def get_num_mem_cgroups(prog: Program) -> None:
+    active_mem_cgroups = get_num_active_mem_cgroups(prog)
+    dying_mem_cgroups = get_num_dying_mem_cgroups(prog)
+    print(
+        f"There are {active_mem_cgroups} active and {dying_mem_cgroups} dying memcgroups \n"
+    )
+
+
+# By default (max_pages == 0) we scan all pages,
+# that have memcg ref but if max_pages is specified
+# then we bail out after getting those many pages
+# or after scanning all pages , whichever happens first.
+def dump_page_cache_pages_pinning_cgroups(prog: Program, max_pages: int = 0):
+    """
+    Dump page-cache pages that have reference to a mem-cgroup.
+    The ouput also contains information such as the cgroup that is pinned, its flags
+    (to indicate current state of cgroup) and file cached by this page.
+
+    :params: max_pages: specify how many pages to find. By default first 10000 such
+    pages are listed. Use 0 to list all such pages.
+
+    """
+    mem_cgroup_root = prog["cgroup_subsys"][_MEMORY_CGRP_ID].root
+    total_count = 0
+    found_count = 0
+    fault_count = 0
+    for page in for_each_page(prog):
+        total_count = total_count + 1
+        try:
+            # Ignore slab pages
+            if PageSlab(page):
+                continue
+            # Ignore non page-cache pages
+            if not page.mapping:
+                continue
+            try:
+                mem_cgroup = page.mem_cgroup
+            except AttributeError:
+                mem_cgroup = page.memcg_data
+
+            if not mem_cgroup.value_() or mem_cgroup.value_() & 3:
+                continue
+            cgroup_subsys_state = cast(
+                "struct cgroup_subsys_state *", mem_cgroup
+            )
+            if cgroup_subsys_state.cgroup.root == mem_cgroup_root:
+                found_count = found_count + 1
+                cgrp = cgroup_subsys_state.cgroup
+                address_space = page.mapping
+                inode = address_space.host
+                if inode_path(inode) is None:
+                    continue
+                dentry = container_of(
+                    inode.i_dentry.first, "struct dentry", "d_u.d_alias"
+                )
+                path = dentry_path_any_mount(dentry).decode()
+                cgroup_state = decode_css_flags(cgrp.self.address_of_())
+                print(
+                    f"page: 0x{page.value_():x} cgroup: {cgroup_path(cgrp).decode()} state: {cgroup_state} path: {path}\n"
+                )
+                if max_pages and found_count == max_pages:
+                    break
+        except FaultError:
+            fault_count = fault_count + 1
+            continue
+
+    print(
+        f"Scanned {total_count} pages, found {found_count} pages with memory cgroup refs, found {fault_count} faults."
+    )
+
+
+class NumMemCgroups(CorelensModule):
+    """Print number of active and dying memcgroups"""
+
+    name = "num-memcgroups"
+
+    def run(self, prog: Program, args: argparse.Namespace) -> None:
+        get_num_mem_cgroups(prog)
+
+
+class PagesPinningMemcgroups(CorelensModule):
+    """Print information related to pages, that are pinning memcgroup(s)"""
+
+    name = "pages-pinning-memcg"
+    run_when = "never"
+
+    def add_args(self, parser: argparse.ArgumentParser) -> None:
+        parser.add_argument(
+            "--max",
+            "-m",
+            type=int,
+            default=0,
+            help="Maximum number of pages to show. By default(0) all such pages are shown.",
+        )
+
+    def run(self, prog: Program, args: argparse.Namespace) -> None:
+        dump_page_cache_pages_pinning_cgroups(prog, max_pages=args.max)