linux-kernel - Re: [PATCH 13/15] stackdepot: add backwards links to hash table buckets

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Message-ID: <ZO8KzKWszioRKrks@elver.google.com>
Date:   Wed, 30 Aug 2023 11:24:28 +0200
From:   Marco Elver <elver@...gle.com>
To:     andrey.konovalov@...ux.dev
Cc:     Alexander Potapenko <glider@...gle.com>,
        Andrey Konovalov <andreyknvl@...il.com>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Vlastimil Babka <vbabka@...e.cz>, kasan-dev@...glegroups.com,
        Evgenii Stepanov <eugenis@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org,
        Andrey Konovalov <andreyknvl@...gle.com>
Subject: Re: [PATCH 13/15] stackdepot: add backwards links to hash table
 buckets

On Tue, Aug 29, 2023 at 07:11PM +0200, andrey.konovalov@...ux.dev wrote:
> From: Andrey Konovalov <andreyknvl@...gle.com>
> 
> Maintain links in the stack records to previous entries within the
> hash table buckets.
> 
> This is preparatory patch for implementing the eviction of stack records
> from the stack depot.
> 
> Signed-off-by: Andrey Konovalov <andreyknvl@...gle.com>
> ---
>  lib/stackdepot.c | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/lib/stackdepot.c b/lib/stackdepot.c
> index a84c0debbb9e..641db97d8c7c 100644
> --- a/lib/stackdepot.c
> +++ b/lib/stackdepot.c
> @@ -58,6 +58,7 @@ union handle_parts {
>  
>  struct stack_record {
>  	struct stack_record *next;	/* Link in hash table or freelist */
> +	struct stack_record *prev;	/* Link in hash table */

At this point this could be a normal list_head? Then you don't have to
roll your own doubly-linked list manipulation (and benefit from things
like CONFIG_LIST_DEBUG).

>  	u32 hash;			/* Hash in hash table */
>  	u32 size;			/* Number of stored frames */
>  	union handle_parts handle;
> @@ -493,6 +494,9 @@ depot_stack_handle_t __stack_depot_save(unsigned long *entries,
>  
>  		if (new) {
>  			new->next = *bucket;
> +			new->prev = NULL;
> +			if (*bucket)
> +				(*bucket)->prev = new;
>  			*bucket = new;
>  			found = new;
>  		}
> -- 
> 2.25.1
>