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    Subject[PATCH 1/3] lib/stackdepot: Add a refcount field in stack_record
    Date
    We want to filter out page_owner output and print only those
    stacks that have been repeated beyond a certain threshold.
    This gives us the chance to get rid of a lot of noise.
    In order to do that, we need to keep track of how many repeated stacks
    (for allocation) do we have, so we add a new refcount_t field
    in the stack_record struct.

    Note that on __set_page_owner_handle(), page_owner->handle is set,
    and on __reset_page_owner(), page_owner->free_handle is set.

    We are interested in page_owner->handle, so when __set_page_owner()
    gets called, we derive the stack_record struct from page_owner->handle,
    and we increment its refcount_t field; and when __reset_page_owner()
    gets called, we derive its stack_record from page_owner->handle()
    and we decrement its refcount_t field.

    This is a preparation for patch#2.

    Signed-off-by: Oscar Salvador <osalvador@suse.de>
    ---
    include/linux/stackdepot.h | 13 ++++++-
    lib/stackdepot.c | 79 +++++++++++++++++++++++++++++++-------
    mm/kasan/common.c | 3 +-
    mm/page_owner.c | 13 +++++--
    4 files changed, 88 insertions(+), 20 deletions(-)

    diff --git a/include/linux/stackdepot.h b/include/linux/stackdepot.h
    index bc2797955de9..5ee0cf5be88f 100644
    --- a/include/linux/stackdepot.h
    +++ b/include/linux/stackdepot.h
    @@ -15,9 +15,16 @@

    typedef u32 depot_stack_handle_t;

    +typedef enum stack_action {
    + STACK_ACTION_NONE,
    + STACK_ACTION_INC,
    +}stack_action_t;
    +
    depot_stack_handle_t __stack_depot_save(unsigned long *entries,
    unsigned int nr_entries,
    - gfp_t gfp_flags, bool can_alloc);
    + gfp_t gfp_flags, bool can_alloc,
    + stack_action_t action);
    +void stack_depot_dec_count(depot_stack_handle_t handle);

    /*
    * Every user of stack depot has to call stack_depot_init() during its own init
    @@ -55,6 +62,10 @@ static inline int stack_depot_early_init(void) { return 0; }

    depot_stack_handle_t stack_depot_save(unsigned long *entries,
    unsigned int nr_entries, gfp_t gfp_flags);
    +depot_stack_handle_t stack_depot_save_action(unsigned long *entries,
    + unsigned int nr_entries,
    + gfp_t gfp_flags,
    + stack_action_t action);

    unsigned int stack_depot_fetch(depot_stack_handle_t handle,
    unsigned long **entries);
    diff --git a/lib/stackdepot.c b/lib/stackdepot.c
    index 5ca0d086ef4a..aeb59d3557e2 100644
    --- a/lib/stackdepot.c
    +++ b/lib/stackdepot.c
    @@ -63,6 +63,7 @@ struct stack_record {
    u32 hash; /* Hash in the hastable */
    u32 size; /* Number of frames in the stack */
    union handle_parts handle;
    + refcount_t count; /* Number of the same repeated stacks */
    unsigned long entries[]; /* Variable-sized array of entries. */
    };

    @@ -139,6 +140,7 @@ depot_alloc_stack(unsigned long *entries, int size, u32 hash, void **prealloc)
    stack->handle.slabindex = depot_index;
    stack->handle.offset = depot_offset >> STACK_ALLOC_ALIGN;
    stack->handle.valid = 1;
    + refcount_set(&stack->count, 1);
    memcpy(stack->entries, entries, flex_array_size(stack, entries, size));
    depot_offset += required_size;

    @@ -302,6 +304,29 @@ void stack_depot_print(depot_stack_handle_t stack)
    }
    EXPORT_SYMBOL_GPL(stack_depot_print);

    +static struct stack_record *stack_depot_getstack(depot_stack_handle_t handle)
    +{
    + union handle_parts parts = { .handle = handle };
    + void *slab;
    + size_t offset = parts.offset << STACK_ALLOC_ALIGN;
    + struct stack_record *stack;
    +
    + if(!handle)
    + return NULL;
    +
    + if (parts.slabindex > depot_index) {
    + WARN(1, "slab index %d out of bounds (%d) for stack id %08x\n",
    + parts.slabindex, depot_index, handle);
    + return NULL;
    + }
    + slab = stack_slabs[parts.slabindex];
    + if (!slab)
    + return NULL;
    +
    + stack = slab + offset;
    + return stack;
    +}
    +
    /**
    * stack_depot_fetch - Fetch stack entries from a depot
    *
    @@ -314,30 +339,42 @@ EXPORT_SYMBOL_GPL(stack_depot_print);
    unsigned int stack_depot_fetch(depot_stack_handle_t handle,
    unsigned long **entries)
    {
    - union handle_parts parts = { .handle = handle };
    - void *slab;
    - size_t offset = parts.offset << STACK_ALLOC_ALIGN;
    struct stack_record *stack;

    *entries = NULL;
    if (!handle)
    return 0;

    - if (parts.slabindex > depot_index) {
    - WARN(1, "slab index %d out of bounds (%d) for stack id %08x\n",
    - parts.slabindex, depot_index, handle);
    - return 0;
    - }
    - slab = stack_slabs[parts.slabindex];
    - if (!slab)
    + stack = stack_depot_getstack(handle);
    + if (!stack)
    return 0;
    - stack = slab + offset;

    *entries = stack->entries;
    return stack->size;
    }
    EXPORT_SYMBOL_GPL(stack_depot_fetch);

    +static void stack_depot_inc_count(struct stack_record *stack)
    +{
    + refcount_inc(&stack->count);
    +}
    +
    +void stack_depot_dec_count(depot_stack_handle_t handle)
    +{
    + struct stack_record *stack = NULL;
    +
    + stack = stack_depot_getstack(handle);
    + if (stack) {
    + /*
    + * page_owner creates some stacks via create_dummy_stack().
    + * We are not interested in those, so make sure we only decrement
    + * "valid" stacks.
    + */
    + if (refcount_read(&stack->count) > 1)
    + refcount_dec(&stack->count);
    + }
    +}
    +
    /**
    * __stack_depot_save - Save a stack trace from an array
    *
    @@ -363,7 +400,8 @@ EXPORT_SYMBOL_GPL(stack_depot_fetch);
    */
    depot_stack_handle_t __stack_depot_save(unsigned long *entries,
    unsigned int nr_entries,
    - gfp_t alloc_flags, bool can_alloc)
    + gfp_t alloc_flags, bool can_alloc,
    + stack_action_t action)
    {
    struct stack_record *found = NULL, **bucket;
    depot_stack_handle_t retval = 0;
    @@ -449,8 +487,11 @@ depot_stack_handle_t __stack_depot_save(unsigned long *entries,
    /* Nobody used this memory, ok to free it. */
    free_pages((unsigned long)prealloc, STACK_ALLOC_ORDER);
    }
    - if (found)
    + if (found) {
    retval = found->handle.handle;
    + if (action == STACK_ACTION_INC)
    + stack_depot_inc_count(found);
    + }
    fast_exit:
    return retval;
    }
    @@ -472,6 +513,16 @@ depot_stack_handle_t stack_depot_save(unsigned long *entries,
    unsigned int nr_entries,
    gfp_t alloc_flags)
    {
    - return __stack_depot_save(entries, nr_entries, alloc_flags, true);
    + return __stack_depot_save(entries, nr_entries, alloc_flags, true,
    + STACK_ACTION_NONE);
    }
    EXPORT_SYMBOL_GPL(stack_depot_save);
    +
    +depot_stack_handle_t stack_depot_save_action(unsigned long *entries,
    + unsigned int nr_entries,
    + gfp_t alloc_flags,
    + stack_action_t action)
    +{
    + return __stack_depot_save(entries, nr_entries, alloc_flags, true, action);
    +}
    +EXPORT_SYMBOL_GPL(stack_depot_save_action);
    diff --git a/mm/kasan/common.c b/mm/kasan/common.c
    index c40c0e7b3b5f..f434994f3b0d 100644
    --- a/mm/kasan/common.c
    +++ b/mm/kasan/common.c
    @@ -36,7 +36,8 @@ depot_stack_handle_t kasan_save_stack(gfp_t flags, bool can_alloc)
    unsigned int nr_entries;

    nr_entries = stack_trace_save(entries, ARRAY_SIZE(entries), 0);
    - return __stack_depot_save(entries, nr_entries, flags, can_alloc);
    + return __stack_depot_save(entries, nr_entries, flags, can_alloc,
    + STACK_ACTION_NONE);
    }

    void kasan_set_track(struct kasan_track *track, gfp_t flags)
    diff --git a/mm/page_owner.c b/mm/page_owner.c
    index e4c6f3f1695b..794f346d7520 100644
    --- a/mm/page_owner.c
    +++ b/mm/page_owner.c
    @@ -106,7 +106,7 @@ static inline struct page_owner *get_page_owner(struct page_ext *page_ext)
    return (void *)page_ext + page_owner_ops.offset;
    }

    -static noinline depot_stack_handle_t save_stack(gfp_t flags)
    +static noinline depot_stack_handle_t save_stack(gfp_t flags, stack_action_t action)
    {
    unsigned long entries[PAGE_OWNER_STACK_DEPTH];
    depot_stack_handle_t handle;
    @@ -125,7 +125,7 @@ static noinline depot_stack_handle_t save_stack(gfp_t flags)
    current->in_page_owner = 1;

    nr_entries = stack_trace_save(entries, ARRAY_SIZE(entries), 2);
    - handle = stack_depot_save(entries, nr_entries, flags);
    + handle = stack_depot_save_action(entries, nr_entries, flags, action);
    if (!handle)
    handle = failure_handle;

    @@ -138,6 +138,7 @@ void __reset_page_owner(struct page *page, unsigned short order)
    int i;
    struct page_ext *page_ext;
    depot_stack_handle_t handle;
    + depot_stack_handle_t alloc_handle;
    struct page_owner *page_owner;
    u64 free_ts_nsec = local_clock();

    @@ -145,7 +146,10 @@ void __reset_page_owner(struct page *page, unsigned short order)
    if (unlikely(!page_ext))
    return;

    - handle = save_stack(GFP_NOWAIT | __GFP_NOWARN);
    + page_owner = get_page_owner(page_ext);
    + alloc_handle = page_owner->handle;
    +
    + handle = save_stack(GFP_NOWAIT | __GFP_NOWARN, STACK_ACTION_NONE);
    for (i = 0; i < (1 << order); i++) {
    __clear_bit(PAGE_EXT_OWNER_ALLOCATED, &page_ext->flags);
    page_owner = get_page_owner(page_ext);
    @@ -153,6 +157,7 @@ void __reset_page_owner(struct page *page, unsigned short order)
    page_owner->free_ts_nsec = free_ts_nsec;
    page_ext = page_ext_next(page_ext);
    }
    + stack_depot_dec_count(alloc_handle);
    }

    static inline void __set_page_owner_handle(struct page_ext *page_ext,
    @@ -189,7 +194,7 @@ noinline void __set_page_owner(struct page *page, unsigned short order,
    if (unlikely(!page_ext))
    return;

    - handle = save_stack(gfp_mask);
    + handle = save_stack(gfp_mask, STACK_ACTION_INC);
    __set_page_owner_handle(page_ext, handle, order, gfp_mask);
    }

    --
    2.35.3
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