[PATCH v2 00/39] Memory allocation profiling

Suren Baghdasaryan
2023-10-24T13:46:45Z

Updates since the last version [1]
- Simplified allocation tagging macros;
- Runtime enable/disable sysctl switch (/proc/sys/vm/mem_profiling)
instead of kernel command-line option;
- CONFIG_MEM_ALLOC_PROFILING_BY_DEFAULT to select default enable state;
- Changed the user-facing API from debugfs to procfs (/proc/allocinfo);
- Removed context capture support to make patch incremental;
- Renamed uninstrumented allocation functions to use _noprof suffix;
- Added __GFP_LAST_BIT to make the code cleaner;
- Removed lazy per-cpu counters; it turned out the memory savings was
minimal and not worth the performance impact;

Things we could not address:
- Alternative way of instrument allocation functions. We discussed an
alternative way of instrumenting the allocators and Steven Rostedt wrote
a proposal [2] to provide compiler support for Callsite Trampolines - a
special attribution of functions to be instrumented. So far we spoke to
representatives of GNU and CLANG communities, will be presenting a
proposal at LPC 2023 and we are working on a proof of concept for CLANG
(see [example 1]). While we will keep working with compiler community on
adding this support, posting the latest version of the patchset as an
immediately available solution until compiler support is implemented;
- Reclaim memory used by pageexts, slabexts, pcpuexts when profiling is
disabled. The main obstacles of reclaiming the memory used for profiling:
1. References from already allocated objects still point to the
allocation tags we are trying to reclaim; We would have to scan and
kill all references before reclaiming;
2. pageext memory is allocated during early boot when fragmentation is
low. Once reclaimed we might not be able to get it back;
3. pageext and slabext objects used for profiling can be interleaved
with other data. Reformatting these vectors of objects at runtime is
a complex and racy task.

Overview

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. The data is exposed to the user space
via /proc/allocinfo interface. Usage example:

$ sort -hr /proc/allocinfo | 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

Support for more detailed allocation context including pid, tgid, task
name, allocation size, timestamp and call stack is not posted in this
patchset to keep it small.

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 [3].
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 for 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:
CONFIG_CODE_TAGGING - to enable code tagging framework.
CONFIG_MEM_ALLOC_PROFILING - enables memory allocation profiling.
CONFIG_MEM_ALLOC_PROFILING_ENABLED_BY_DEFAULT - enables memory allocation
profiling by default.
CONFIG_MEM_ALLOC_PROFILING_DEBUG - enables memory allocation profiling
validation.
Note: CONFIG_MEM_ALLOC_PROFILING enables CONFIG_PAGE_EXTENSION to store
code tag reference in the page_ext object.

/proc/sys/vm/mem_profiling sysctl is provided to enable/disable the
functionality and avoid the performance overhead.

Overhead
To measure the overhead we are comparing the following configurations:
(1) Baseline
(2) Disabled by default (CONFIG_MEM_ALLOC_PROFILING &
!CONFIG_MEM_ALLOC_PROFILING_BY_DEFAULT)
(3) Enabled by default (CONFIG_MEM_ALLOC_PROFILING &
CONFIG_MEM_ALLOC_PROFILING_BY_DEFAULT)
(4) Enabled at runtime (CONFIG_MEM_ALLOC_PROFILING &
!CONFIG_MEM_ALLOC_PROFILING_BY_DEFAULT & /proc/sys/vm/mem_profiling=1)
(5) Memcg (CONFIG_MEMCG_KMEM)
(6) Enabled by default with memcg (CONFIG_MEM_ALLOC_PROFILING &
CONFIG_MEM_ALLOC_PROFILING_BY_DEFAULT & CONFIG_MEMCG_KMEM)

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 and (for comparison purposes) baseline with
CONFIG_MEMCG_KMEM enabled and allocations using __GFP_ACCOUNT:

kmalloc pgalloc
(1 baseline) 12.041s 49.190s
(2 default disabled) 14.970s (+24.33%) 49.684s (+1.00%)
(3 default enabled) 16.859s (+40.01%) 56.287s (+14.43%)
(4 runtime enabled) 16.983s (+41.04%) 55.760s (+13.36%)
(5 memcg) 33.831s (+180.96%) 51.433s (+4.56%)
(6 enabled & memcg) 39.145s (+225.10%) 56.874s (+15.62%)

Memory overhead:
Kernel size:

text data bss dec hex
(1) 32638461 18286426 18325508 69250395 420ad5b
(2) 32710110 18646586 18071556 69428252 423641c
(3) 32706918 18646586 18071556 69425060 42357a4
(4) 32709664 18646586 18071556 69427806 423625e
(5) 32715893 18345334 18239492 69300719 42171ef
(6) 32786068 18701958 17993732 69481758 424351e

Memory consumption on a 56 core Intel CPU with 125GB of memory running
Fedora:
Code tags: 192 kB
PageExts: 262144 kB (256MB)
SlabExts: 9876 kB (9.6MB)
PcpuExts: 512 kB (0.5MB)

Total overhead is 0.2% of total memory.

[1] https://lore.kernel.org/all/20230501165450.15352-1-surenb@google.com/
[2] https://docs.google.com/presentation/d/1zQnuMbEfcq9lHUXgJRUZsd1McRAkr3Xq6Wk693YA0To/edit?usp=sharing
[3] https://lore.kernel.org/all/20220830214919.53220-1-surenb@google.com/

[example 1]:
typedef struct codetag {
const char* file;
int line;
int counter;
} codetag;

void my_trampoline(func_ptr func, ...) {
static codetag callsite_data __section("alloc_tags") =
{ __callsite_FILE, __callsite_LINE, 0 };
callsite_data.counter++;
func(...);
}

__callsite_wrapper(my_trampoline)
__attribute__ ((always_inline))
static inline void foo1(void) {
printf("foo1 function\n");
}

__callsite_wrapper(my_trampoline)
__attribute__ ((always_inline))
static inline void foo2(void) {
printf("foo2 function\n");
}

void bar(void) {
foo1();
}

int main(int argc, char** argv) {
foo1();
foo2();
bar();
return 0;
}

Kent Overstreet (16):
lib/string_helpers: Add flags param to string_get_size()
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
change alloc_pages name in ivpu_bo_ops to avoid conflicts
mm/slub: Mark slab_free_freelist_hook() __always_inline
mempool: Hook up to memory allocation profiling
xfs: Memory allocation profiling fixups
timekeeping: Fix a circular include dependency
mm: percpu: Introduce pcpuobj_ext
mm: percpu: Add codetag reference into pcpuobj_ext
arm64: Fix circular header dependency
mm: vmalloc: Enable memory allocation profiling
rhashtable: Plumb through alloc tag
MAINTAINERS: Add entries for code tagging and memory allocation
profiling

Suren Baghdasaryan (23):
mm: enumerate all gfp flags
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: create new codetag references during page splitting
mm/page_ext: enable early_page_ext when
CONFIG_MEM_ALLOC_PROFILING_DEBUG=y
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
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

Documentation/admin-guide/sysctl/vm.rst | 16 ++
Documentation/filesystems/proc.rst | 28 ++
MAINTAINERS | 16 ++
arch/arm64/include/asm/spectre.h | 4 +-
arch/powerpc/mm/book3s64/radix_pgtable.c | 2 +-
arch/x86/kernel/amd_gart_64.c | 2 +-
drivers/accel/ivpu/ivpu_gem.c | 8 +-
drivers/accel/ivpu/ivpu_gem.h | 2 +-
drivers/block/virtio_blk.c | 4 +-
drivers/gpu/drm/gud/gud_drv.c | 2 +-
drivers/iommu/dma-iommu.c | 2 +-
drivers/mmc/core/block.c | 4 +-
drivers/mtd/spi-nor/debugfs.c | 6 +-
.../ethernet/chelsio/cxgb4/cxgb4_debugfs.c | 4 +-
drivers/scsi/sd.c | 8 +-
drivers/staging/media/atomisp/pci/hmm/hmm.c | 2 +-
drivers/xen/grant-dma-ops.c | 2 +-
drivers/xen/swiotlb-xen.c | 2 +-
fs/xfs/kmem.c | 4 +-
fs/xfs/kmem.h | 10 +-
include/asm-generic/codetag.lds.h | 14 +
include/asm-generic/vmlinux.lds.h | 3 +
include/linux/alloc_tag.h | 188 +++++++++++++
include/linux/codetag.h | 83 ++++++
include/linux/dma-map-ops.h | 2 +-
include/linux/fortify-string.h | 5 +-
include/linux/fs.h | 6 +-
include/linux/gfp.h | 111 +++++---
include/linux/gfp_types.h | 101 +++++--
include/linux/hrtimer.h | 2 +-
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 | 23 +-
include/linux/pgalloc_tag.h | 105 +++++++
include/linux/prandom.h | 1 -
include/linux/rhashtable-types.h | 11 +-
include/linux/sched.h | 26 +-
include/linux/slab.h | 180 ++++++------
include/linux/slab_def.h | 2 +-
include/linux/slub_def.h | 4 +-
include/linux/string.h | 4 +-
include/linux/string_helpers.h | 13 +-
include/linux/time_namespace.h | 2 +
include/linux/vmalloc.h | 60 +++-
init/Kconfig | 4 +
kernel/dma/mapping.c | 4 +-
kernel/kallsyms_selftest.c | 2 +-
kernel/module/main.c | 25 +-
lib/Kconfig.debug | 31 +++
lib/Makefile | 3 +
lib/alloc_tag.c | 212 ++++++++++++++
lib/codetag.c | 258 ++++++++++++++++++
lib/rhashtable.c | 52 +++-
lib/string_helpers.c | 24 +-
lib/test-string_helpers.c | 4 +-
mm/compaction.c | 7 +-
mm/filemap.c | 6 +-
mm/huge_memory.c | 2 +
mm/hugetlb.c | 8 +-
mm/kfence/core.c | 14 +-
mm/kfence/kfence.h | 4 +-
mm/memcontrol.c | 56 +---
mm/mempolicy.c | 42 +--
mm/mempool.c | 34 +--
mm/mm_init.c | 1 +
mm/page_alloc.c | 66 +++--
mm/page_ext.c | 13 +
mm/page_owner.c | 2 +-
mm/percpu-internal.h | 26 +-
mm/percpu.c | 120 ++++----
mm/show_mem.c | 15 +
mm/slab.c | 24 +-
mm/slab.h | 246 +++++++++++++----
mm/slab_common.c | 96 +++++--
mm/slub.c | 26 +-
mm/util.c | 44 +--
mm/vmalloc.c | 88 +++---
scripts/kallsyms.c | 13 +
scripts/module.lds.S | 7 +
85 files changed, 2117 insertions(+), 698 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/nodemask_types.h
create mode 100644 include/linux/pgalloc_tag.h
create mode 100644 lib/alloc_tag.c
create mode 100644 lib/codetag.c

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2.42.0.758.gaed0368e0e-goog