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    Subject[PATCH v2 00/39] Memory allocation profiling
    From
    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

    --
    2.42.0.758.gaed0368e0e-goog

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