linux-kernel - Re: [PATCH v4 14/36] lib: add allocation tagging support for memory allocation profiling

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Message-ID: <b62d2ace-4619-40ac-8536-c5626e95d87b@suse.cz>
Date: Wed, 28 Feb 2024 09:41:23 +0100
From: Vlastimil Babka <vbabka@...e.cz>
To: Suren Baghdasaryan <surenb@...gle.com>, akpm@...ux-foundation.org
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Subject: Re: [PATCH v4 14/36] lib: add allocation tagging support for memory
 allocation profiling

Another thing I noticed, dunno how critical

On 2/21/24 20:40, Suren Baghdasaryan wrote:
> +static inline void __alloc_tag_sub(union codetag_ref *ref, size_t bytes)
> +{
> +	struct alloc_tag *tag;
> +
> +#ifdef CONFIG_MEM_ALLOC_PROFILING_DEBUG
> +	WARN_ONCE(ref && !ref->ct, "alloc_tag was not set\n");
> +#endif
> +	if (!ref || !ref->ct)
> +		return;

This is quite careful.

> +
> +	tag = ct_to_alloc_tag(ref->ct);
> +
> +	this_cpu_sub(tag->counters->bytes, bytes);
> +	this_cpu_dec(tag->counters->calls);
> +
> +	ref->ct = NULL;
> +}
> +
> +static inline void alloc_tag_sub(union codetag_ref *ref, size_t bytes)
> +{
> +	__alloc_tag_sub(ref, bytes);
> +}
> +
> +static inline void alloc_tag_sub_noalloc(union codetag_ref *ref, size_t bytes)
> +{
> +	__alloc_tag_sub(ref, bytes);
> +}
> +
> +static inline void alloc_tag_ref_set(union codetag_ref *ref, struct alloc_tag *tag)
> +{
> +#ifdef CONFIG_MEM_ALLOC_PROFILING_DEBUG
> +	WARN_ONCE(ref && ref->ct,
> +		  "alloc_tag was not cleared (got tag for %s:%u)\n",\
> +		  ref->ct->filename, ref->ct->lineno);
> +
> +	WARN_ONCE(!tag, "current->alloc_tag not set");
> +#endif
> +	if (!ref || !tag)
> +		return;

This too.

> +
> +	ref->ct = &tag->ct;
> +	/*
> +	 * We need in increment the call counter every time we have a new
> +	 * allocation or when we split a large allocation into smaller ones.
> +	 * Each new reference for every sub-allocation needs to increment call
> +	 * counter because when we free each part the counter will be decremented.
> +	 */
> +	this_cpu_inc(tag->counters->calls);
> +}
> +
> +static inline void alloc_tag_add(union codetag_ref *ref, struct alloc_tag *tag, size_t bytes)
> +{
> +	alloc_tag_ref_set(ref, tag);

We might have returned from alloc_tag_ref_set() due to !tag

> +	this_cpu_add(tag->counters->bytes, bytes);

But here we still assume it's valid.

> +}
> +