On Fri, 9 Feb 2024 at 00:45, Oscar Salvador <osalvador@xxxxxxx> wrote:
>
> page_owner needs to increment a stack_record refcount when a new allocation
> occurs, and decrement it on a free operation.
> In order to do that, we need to have a way to get a stack_record from a
> handle.
> Implement stack_depot_get_stack() which just does that, and make it public
> so page_owner can use it.
>
> Also implement {inc,dec}_stack_record_count() which increments
> or decrements on respective allocation and free operations, via
> __reset_page_owner() (free operation) and __set_page_owner() (alloc
> operation).
>
> Signed-off-by: Oscar Salvador <osalvador@xxxxxxx>
> ---
> include/linux/stackdepot.h | 8 ++++++++
> lib/stackdepot.c | 8 ++++++++
> mm/page_owner.c | 30 ++++++++++++++++++++++++++++++
> 3 files changed, 46 insertions(+)
>
> diff --git a/include/linux/stackdepot.h b/include/linux/stackdepot.h
> index d0dcf4aebfb4..ac62de4d4999 100644
> --- a/include/linux/stackdepot.h
> +++ b/include/linux/stackdepot.h
> @@ -175,6 +175,14 @@ depot_stack_handle_t stack_depot_save_flags(unsigned long *entries,
> depot_stack_handle_t stack_depot_save(unsigned long *entries,
> unsigned int nr_entries, gfp_t gfp_flags);
>
> +/**
> + * stack_depo_get_stack - Get a pointer to a stack struct
> + * @handle: Stack depot handle
> + *
> + * Return: Returns a pointer to a stack struct
> + */
> +struct stack_record *stack_depot_get_stack(depot_stack_handle_t handle);
> +
> /**
> * stack_depot_fetch - Fetch a stack trace from stack depot
> *
> diff --git a/lib/stackdepot.c b/lib/stackdepot.c
> index 16c8a1bf0008..197c355601f9 100644
> --- a/lib/stackdepot.c
> +++ b/lib/stackdepot.c
> @@ -681,6 +681,14 @@ depot_stack_handle_t stack_depot_save(unsigned long *entries,
> }
> EXPORT_SYMBOL_GPL(stack_depot_save);
>
> +struct stack_record *stack_depot_get_stack(depot_stack_handle_t handle)
> +{
> + if (!handle)
> + return NULL;
> +
> + return depot_fetch_stack(handle);
> +}
> +
> unsigned int stack_depot_fetch(depot_stack_handle_t handle,
> unsigned long **entries)
> {
> diff --git a/mm/page_owner.c b/mm/page_owner.c
> index 5634e5d890f8..0adf41702b9d 100644
> --- a/mm/page_owner.c
> +++ b/mm/page_owner.c
> @@ -61,6 +61,22 @@ static __init bool need_page_owner(void)
> return page_owner_enabled;
> }
>
> +static void inc_stack_record_count(depot_stack_handle_t handle)
> +{
> + struct stack_record *stack = stack_depot_get_stack(handle);
> +
> + if (stack)
> + refcount_inc(&stack->count);
> +}
> +
> +static void dec_stack_record_count(depot_stack_handle_t handle)
> +{
> + struct stack_record *stack = stack_depot_get_stack(handle);
> +
> + if (stack)
> + refcount_dec(&stack->count);
> +}
> +
> static __always_inline depot_stack_handle_t create_dummy_stack(void)
> {
> unsigned long entries[4];
> @@ -140,6 +156,7 @@ 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();
>
> @@ -147,6 +164,9 @@ void __reset_page_owner(struct page *page, unsigned short order)
> if (unlikely(!page_ext))
> return;
>
> + page_owner = get_page_owner(page_ext);
> + alloc_handle = page_owner->handle;
> +
> handle = save_stack(GFP_NOWAIT | __GFP_NOWARN);
> for (i = 0; i < (1 << order); i++) {
> __clear_bit(PAGE_EXT_OWNER_ALLOCATED, &page_ext->flags);
> @@ -158,6 +178,15 @@ void __reset_page_owner(struct page *page, unsigned short order)
> page_ext = page_ext_next(page_ext);
> }
> page_ext_put(page_ext);
> + if (alloc_handle != early_handle)
> + /*
> + * early_handle is being set as a handle for all those
> + * early allocated pages. See init_pages_in_zone().
> + * Since their refcount is not being incremented because
> + * the machinery is not ready yet, we cannot decrement
> + * their refcount either.
> + */
> + dec_stack_record_count(alloc_handle);
> }
>
> static inline void __set_page_owner_handle(struct page_ext *page_ext,
> @@ -199,6 +228,7 @@ noinline void __set_page_owner(struct page *page, unsigned short order,
> return;
> __set_page_owner_handle(page_ext, handle, order, gfp_mask);
> page_ext_put(page_ext);
> + inc_stack_record_count(handle);
> }
>
> void __set_page_owner_migrate_reason(struct page *page, int reason)
> --
> 2.43.0
>
