linux-kernel - Re: [PATCH v4 5/6] alloc_tag: introduce pgtag_ref

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Message-Id: <20241023140017.e165544bf20bcb0c79bfee57@linux-foundation.org>
Date: Wed, 23 Oct 2024 14:00:17 -0700
From: Andrew Morton <akpm@...ux-foundation.org>
To: Suren Baghdasaryan <surenb@...gle.com>
Cc: kent.overstreet@...ux.dev, corbet@....net, arnd@...db.de,
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Subject: Re: [PATCH v4 5/6] alloc_tag: introduce pgtag_ref_handle to
 abstract page tag references

On Wed, 23 Oct 2024 10:07:58 -0700 Suren Baghdasaryan <surenb@...gle.com> wrote:

> To simplify later changes to page tag references, introduce new
> pgtag_ref_handle type. This allows easy replacement of page_ext
> as a storage of page allocation tags.
> 
> ...
>
>  static inline void pgalloc_tag_copy(struct folio *new, struct folio *old)
>  {
> +	union pgtag_ref_handle handle;
> +	union codetag_ref ref;
>  	struct alloc_tag *tag;
> -	union codetag_ref *ref;
>  
>  	tag = pgalloc_tag_get(&old->page);
>  	if (!tag)
>  		return;
>  
> -	ref = get_page_tag_ref(&new->page);
> -	if (!ref)
> +	if (!get_page_tag_ref(&new->page, &ref, &handle))
>  		return;
>  
>  	/* Clear the old ref to the original allocation tag. */
>  	clear_page_tag_ref(&old->page);
>  	/* Decrement the counters of the tag on get_new_folio. */
> -	alloc_tag_sub(ref, folio_nr_pages(new));
> -
> -	__alloc_tag_ref_set(ref, tag);
> -
> -	put_page_tag_ref(ref);
> +	alloc_tag_sub(&ref, folio_nr_pages(new));

mm-stable has folio_size(new) here, fixed up.

I think we aleady discussed this, but there's a crazy amount of
inlining here.  pgalloc_tag_split() is huge, and has four callsites.