[PATCH 00/40] Memory allocation profiling

Suren Baghdasaryan
2023-05-01T16:55:18Z

Memory allocation profiling infrastructure provides a low overhead
mechanism to make all kernel allocations in the system visible. It can be
used to monitor memory usage, track memory hotspots, detect memory leaks,
identify memory regressions.

To keep the overhead to the minimum, we record only allocation sizes for
every allocation in the codebase. With that information, if users are
interested in more detailed context for a specific allocation, they can
enable in-depth context tracking, which includes capturing the pid, tgid,
task name, allocation size, timestamp and call stack for every allocation
at the specified code location.

The data is exposed to the user space via a read-only debugfs file called
allocations. Usage example:

$ sort -hr /sys/kernel/debug/allocations|head
153MiB 8599 mm/slub.c:1826 module:slub func:alloc_slab_page
6.08MiB 49 mm/slab_common.c:950 module:slab_common func:_kmalloc_order
5.09MiB 6335 mm/memcontrol.c:2814 module:memcontrol func:alloc_slab_obj_exts
4.54MiB 78 mm/page_alloc.c:5777 module:page_alloc func:alloc_pages_exact
1.32MiB 338 include/asm-generic/pgalloc.h:63 module:pgtable func:__pte_alloc_one
1.16MiB 603 fs/xfs/xfs_log_priv.h:700 module:xfs func:xlog_kvmalloc
1.00MiB 256 mm/swap_cgroup.c:48 module:swap_cgroup func:swap_cgroup_prepare
734KiB 5380 fs/xfs/kmem.c:20 module:xfs func:kmem_alloc
640KiB 160 kernel/rcu/tree.c:3184 module:tree func:fill_page_cache_func
640KiB 160 drivers/char/virtio_console.c:452 module:virtio_console func:alloc_buf

For allocation context capture, a new debugfs file called allocations.ctx
is used to select which code location should capture allocation context
and to read captured context information. Usage example:

$ cd /sys/kernel/debug/
$ echo "file include/asm-generic/pgalloc.h line 63 enable" > allocations.ctx
$ cat allocations.ctx
920KiB 230 include/asm-generic/pgalloc.h:63 module:pgtable func:__pte_alloc_one
size: 4096
pid: 1474
tgid: 1474
comm: bash
ts: 175332940994
call stack:
pte_alloc_one+0xfe/0x130
__pte_alloc+0x22/0xb0
copy_page_range+0x842/0x1640
dup_mm+0x42d/0x580
copy_process+0xfb1/0x1ac0
kernel_clone+0x92/0x3e0
__do_sys_clone+0x66/0x90
do_syscall_64+0x38/0x90
entry_SYSCALL_64_after_hwframe+0x63/0xcd
...

Implementation utilizes a more generic concept of code tagging, introduced
as part of this patchset. Code tag is a structure identifying a specific
location in the source code which is generated at compile time and can be
embedded in an application-specific structure. A number of applications
for code tagging have been presented in the original RFC [1].
Code tagging uses the old trick of "define a special elf section for
objects of a given type so that we can iterate over them at runtime" and
creates a proper library for it.

To profile memory allocations, we instrument page, slab and percpu
allocators to record total memory allocated in the associated code tag at
every allocation in the codebase. Every time an allocation is performed by
an instrumented allocator, the code tag at that location increments its
counter by allocation size. Every time the memory is freed the counter is
decremented. To decrement the counter upon freeing, allocated object needs
a reference to its code tag. Page allocators use page_ext to record this
reference while slab allocators use memcg_data (renamed into more generic
slabobj_ext) of the slab page.

Module allocations are accounted the same way as other kernel allocations.
Module loading and unloading is supported. If a module is unloaded while
one or more of its allocations is still not freed (rather rare condition),
its data section will be kept in memory to allow later code tag
referencing when the allocation is freed later on.

As part of this series we introduce several kernel configs:
CODE_TAGGING - to enable code tagging framework
CONFIG_MEM_ALLOC_PROFILING - to enable memory allocation profiling
CONFIG_MEM_ALLOC_PROFILING_DEBUG - to enable memory allocation profiling
validation
Note: CONFIG_MEM_ALLOC_PROFILING enables CONFIG_PAGE_EXTENSION to store
code tag reference in the page_ext object.

nomem_profiling kernel command-line parameter is also provided to disable
the functionality and avoid the performance overhead.
Performance overhead:
To evaluate performance we implemented an in-kernel test executing
multiple get_free_page/free_page and kmalloc/kfree calls with allocation
sizes growing from 8 to 240 bytes with CPU frequency set to max and CPU
affinity set to a specific CPU to minimize the noise. Below is performance
comparison between the baseline kernel, profiling when enabled, profiling
when disabled (nomem_profiling=y) and (for comparison purposes) baseline
with CONFIG_MEMCG_KMEM enabled and allocations using __GFP_ACCOUNT:

kmalloc pgalloc
Baseline (6.3-rc7) 9.200s 31.050s
profiling disabled 9.800 (+6.52%) 32.600 (+4.99%)
profiling enabled 12.500 (+35.87%) 39.010 (+25.60%)
memcg_kmem enabled 41.400 (+350.00%) 70.600 (+127.38%)

[1] https://lore.kernel.org/all/20220830214919.53220-1-surenb@google.com/

Kent Overstreet (15):
lib/string_helpers: Drop space in string_get_size's output
scripts/kallysms: Always include __start and __stop symbols
fs: Convert alloc_inode_sb() to a macro
nodemask: Split out include/linux/nodemask_types.h
prandom: Remove unused include
lib/string.c: strsep_no_empty()
Lazy percpu counters
lib: code tagging query helper functions
mm/slub: Mark slab_free_freelist_hook() __always_inline
mempool: Hook up to memory allocation profiling
timekeeping: Fix a circular include dependency
mm: percpu: Introduce pcpuobj_ext
mm: percpu: Add codetag reference into pcpuobj_ext
arm64: Fix circular header dependency
MAINTAINERS: Add entries for code tagging and memory allocation
profiling

Suren Baghdasaryan (25):
mm: introduce slabobj_ext to support slab object extensions
mm: introduce __GFP_NO_OBJ_EXT flag to selectively prevent slabobj_ext
creation
mm/slab: introduce SLAB_NO_OBJ_EXT to avoid obj_ext creation
mm: prevent slabobj_ext allocations for slabobj_ext and kmem_cache
objects
slab: objext: introduce objext_flags as extension to
page_memcg_data_flags
lib: code tagging framework
lib: code tagging module support
lib: prevent module unloading if memory is not freed
lib: add allocation tagging support for memory allocation profiling
lib: introduce support for page allocation tagging
change alloc_pages name in dma_map_ops to avoid name conflicts
mm: enable page allocation tagging
mm/page_ext: enable early_page_ext when
CONFIG_MEM_ALLOC_PROFILING_DEBUG=y
mm: create new codetag references during page splitting
lib: add codetag reference into slabobj_ext
mm/slab: add allocation accounting into slab allocation and free paths
mm/slab: enable slab allocation tagging for kmalloc and friends
mm: percpu: enable per-cpu allocation tagging
move stack capture functionality into a separate function for reuse
lib: code tagging context capture support
lib: implement context capture support for tagged allocations
lib: add memory allocations report in show_mem()
codetag: debug: skip objext checking when it's for objext itself
codetag: debug: mark codetags for reserved pages as empty
codetag: debug: introduce OBJEXTS_ALLOC_FAIL to mark failed slab_ext
allocations

.../admin-guide/kernel-parameters.txt | 2 +
MAINTAINERS | 22 +
arch/arm64/include/asm/spectre.h | 4 +-
arch/x86/kernel/amd_gart_64.c | 2 +-
drivers/iommu/dma-iommu.c | 2 +-
drivers/xen/grant-dma-ops.c | 2 +-
drivers/xen/swiotlb-xen.c | 2 +-
include/asm-generic/codetag.lds.h | 14 +
include/asm-generic/vmlinux.lds.h | 3 +
include/linux/alloc_tag.h | 161 ++++++
include/linux/codetag.h | 159 ++++++
include/linux/codetag_ctx.h | 48 ++
include/linux/dma-map-ops.h | 2 +-
include/linux/fs.h | 6 +-
include/linux/gfp.h | 123 ++--
include/linux/gfp_types.h | 12 +-
include/linux/hrtimer.h | 2 +-
include/linux/lazy-percpu-counter.h | 102 ++++
include/linux/memcontrol.h | 56 +-
include/linux/mempool.h | 73 ++-
include/linux/mm.h | 8 +
include/linux/mm_types.h | 4 +-
include/linux/nodemask.h | 2 +-
include/linux/nodemask_types.h | 9 +
include/linux/page_ext.h | 1 -
include/linux/pagemap.h | 9 +-
include/linux/percpu.h | 19 +-
include/linux/pgalloc_tag.h | 95 ++++
include/linux/prandom.h | 1 -
include/linux/sched.h | 32 +-
include/linux/slab.h | 182 +++---
include/linux/slab_def.h | 2 +-
include/linux/slub_def.h | 4 +-
include/linux/stackdepot.h | 16 +
include/linux/string.h | 1 +
include/linux/time_namespace.h | 2 +
init/Kconfig | 4 +
kernel/dma/mapping.c | 4 +-
kernel/module/main.c | 25 +-
lib/Kconfig | 3 +
lib/Kconfig.debug | 26 +
lib/Makefile | 5 +
lib/alloc_tag.c | 464 +++++++++++++++
lib/codetag.c | 529 ++++++++++++++++++
lib/lazy-percpu-counter.c | 127 +++++
lib/show_mem.c | 15 +
lib/stackdepot.c | 68 +++
lib/string.c | 19 +
lib/string_helpers.c | 3 +-
mm/compaction.c | 9 +-
mm/filemap.c | 6 +-
mm/huge_memory.c | 2 +
mm/kfence/core.c | 14 +-
mm/kfence/kfence.h | 4 +-
mm/memcontrol.c | 56 +-
mm/mempolicy.c | 30 +-
mm/mempool.c | 28 +-
mm/mm_init.c | 1 +
mm/page_alloc.c | 75 ++-
mm/page_ext.c | 21 +-
mm/page_owner.c | 54 +-
mm/percpu-internal.h | 26 +-
mm/percpu.c | 122 ++--
mm/slab.c | 22 +-
mm/slab.h | 224 ++++++--
mm/slab_common.c | 95 +++-
mm/slub.c | 24 +-
mm/util.c | 10 +-
scripts/kallsyms.c | 13 +
scripts/module.lds.S | 7 +
70 files changed, 2765 insertions(+), 554 deletions(-)
create mode 100644 include/asm-generic/codetag.lds.h
create mode 100644 include/linux/alloc_tag.h
create mode 100644 include/linux/codetag.h
create mode 100644 include/linux/codetag_ctx.h
create mode 100644 include/linux/lazy-percpu-counter.h
create mode 100644 include/linux/nodemask_types.h
create mode 100644 include/linux/pgalloc_tag.h
create mode 100644 lib/alloc_tag.c
create mode 100644 lib/codetag.c
create mode 100644 lib/lazy-percpu-counter.c

--
2.40.1.495.gc816e09b53d-goog