linux-kernel - Re: [PATCH v9 2/7] lib/stackdepot: Move stack_record struct definition into the header

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Message-ID: <CANpmjNPypJM5icG9M5yP5-psSofbA7D35eaKx+E6NyCsHMa=qg@mail.gmail.com>
Date: Thu, 15 Feb 2024 09:16:58 +0100
From: Marco Elver <elver@...gle.com>
To: Oscar Salvador <osalvador@...e.de>
Cc: Andrew Morton <akpm@...ux-foundation.org>, linux-kernel@...r.kernel.org, 
	linux-mm@...ck.org, Michal Hocko <mhocko@...e.com>, Vlastimil Babka <vbabka@...e.cz>, 
	Andrey Konovalov <andreyknvl@...il.com>, Alexander Potapenko <glider@...gle.com>
Subject: Re: [PATCH v9 2/7] lib/stackdepot: Move stack_record struct
 definition into the header

On Wed, 14 Feb 2024 at 18:00, Oscar Salvador <osalvador@...e.de> wrote:
>
> In order to move the heavy lifting into page_owner code, this one
> needs to have access to the stack_record structure, which right now
> sits in lib/stackdepot.c.
> Move it to the stackdepot.h header so page_owner can access
> stack_record's struct fields.
>
> Signed-off-by: Oscar Salvador <osalvador@...e.de>
> Reviewed-by: Marco Elver <elver@...gle.com>
> Reviewed-by: Vlastimil Babka <vbabka@...e.cz>
> ---
>  include/linux/stackdepot.h | 47 ++++++++++++++++++++++++++++++++++++++
>  lib/stackdepot.c           | 45 +-----------------------------------
>  2 files changed, 48 insertions(+), 44 deletions(-)
>
> diff --git a/include/linux/stackdepot.h b/include/linux/stackdepot.h
> index adcbb8f23600..c4b5ad57c066 100644
> --- a/include/linux/stackdepot.h
> +++ b/include/linux/stackdepot.h
> @@ -30,6 +30,53 @@ typedef u32 depot_stack_handle_t;
>   */
>  #define STACK_DEPOT_EXTRA_BITS 5
>
> +#define DEPOT_HANDLE_BITS (sizeof(depot_stack_handle_t) * 8)
> +
> +#define DEPOT_POOL_ORDER 2 /* Pool size order, 4 pages */
> +#define DEPOT_POOL_SIZE (1LL << (PAGE_SHIFT + DEPOT_POOL_ORDER))
> +#define DEPOT_STACK_ALIGN 4
> +#define DEPOT_OFFSET_BITS (DEPOT_POOL_ORDER + PAGE_SHIFT - DEPOT_STACK_ALIGN)
> +#define DEPOT_POOL_INDEX_BITS (DEPOT_HANDLE_BITS - DEPOT_OFFSET_BITS - \
> +                              STACK_DEPOT_EXTRA_BITS)
> +
> +#ifdef CONFIG_STACKDEPOT
> +/* Compact structure that stores a reference to a stack. */
> +union handle_parts {
> +       depot_stack_handle_t handle;
> +       struct {
> +               /* pool_index is offset by 1 */
> +               u32 pool_index  : DEPOT_POOL_INDEX_BITS;
> +               u32 offset      : DEPOT_OFFSET_BITS;
> +               u32 extra       : STACK_DEPOT_EXTRA_BITS;
> +       };
> +};
> +
> +struct stack_record {
> +       struct list_head hash_list;     /* Links in the hash table */
> +       u32 hash;                       /* Hash in hash table */
> +       u32 size;                       /* Number of stored frames */
> +       union handle_parts handle;      /* Constant after initialization */
> +       refcount_t count;
> +       union {
> +               unsigned long entries[CONFIG_STACKDEPOT_MAX_FRAMES];    /* Frames */
> +               struct {
> +                       /*
> +                        * An important invariant of the implementation is to
> +                        * only place a stack record onto the freelist iff its
> +                        * refcount is zero. Because stack records with a zero
> +                        * refcount are never considered as valid, it is safe to
> +                        * union @entries and freelist management state below.
> +                        * Conversely, as soon as an entry is off the freelist
> +                        * and its refcount becomes non-zero, the below must not
> +                        * be accessed until being placed back on the freelist.
> +                        */
> +                       struct list_head free_list;     /* Links in the freelist */
> +                       unsigned long rcu_state;        /* RCU cookie */
> +               };
> +       };
> +};
> +#endif
> +
>  typedef u32 depot_flags_t;
>
>  /*
> diff --git a/lib/stackdepot.c b/lib/stackdepot.c
> index c043a4186bc5..4a661a6777da 100644
> --- a/lib/stackdepot.c
> +++ b/lib/stackdepot.c
> @@ -36,55 +36,12 @@
>  #include <linux/memblock.h>
>  #include <linux/kasan-enabled.h>
>
> -#define DEPOT_HANDLE_BITS (sizeof(depot_stack_handle_t) * 8)
> -
> -#define DEPOT_POOL_ORDER 2 /* Pool size order, 4 pages */
> -#define DEPOT_POOL_SIZE (1LL << (PAGE_SHIFT + DEPOT_POOL_ORDER))
> -#define DEPOT_STACK_ALIGN 4
> -#define DEPOT_OFFSET_BITS (DEPOT_POOL_ORDER + PAGE_SHIFT - DEPOT_STACK_ALIGN)
> -#define DEPOT_POOL_INDEX_BITS (DEPOT_HANDLE_BITS - DEPOT_OFFSET_BITS - \
> -                              STACK_DEPOT_EXTRA_BITS)
>  #define DEPOT_POOLS_CAP 8192
> -/* The pool_index is offset by 1 so the first record does not have a 0 handle. */
> +/* The pool_index is offset by 1 so the first record does not have a 0 handle */

Why this comment change? We lost the '.' -- for future reference, it'd
be good to ensure unnecessary changes don't creep into the diff. This
is just nitpicking, and I've already reviewed this change, so no need
to send a v+1.