Re: [PATCH v4 19/36] mm: create new codetag references during page splitting

[Vlastimil Babka]

On 2/21/24 20:40, Suren Baghdasaryan wrote:
> When a high-order page is split into smaller ones, each newly split
> page should get its codetag. The original codetag is reused for these
> pages but it's recorded as 0-byte allocation because original codetag
> already accounts for the original high-order allocated page.

This was v3 but then you refactored (for the better) so the commit log
could reflect it?

> Signed-off-by: Suren Baghdasaryan <surenb@xxxxxxxxxx>

I was going to R-b, but now I recalled the trickiness of
__free_pages() for non-compound pages if it loses the race to a
speculative reference. Will the codetag handling work fine there?

> ---
>  include/linux/pgalloc_tag.h | 30 ++++++++++++++++++++++++++++++
>  mm/huge_memory.c            |  2 ++
>  mm/page_alloc.c             |  2 ++
>  3 files changed, 34 insertions(+)
> 
> diff --git a/include/linux/pgalloc_tag.h b/include/linux/pgalloc_tag.h
> index b49ab955300f..9e6ad8e0e4aa 100644
> --- a/include/linux/pgalloc_tag.h
> +++ b/include/linux/pgalloc_tag.h
> @@ -67,11 +67,41 @@ static inline void pgalloc_tag_sub(struct page *page, unsigned int order)
>  	}
>  }
>  
> +static inline void pgalloc_tag_split(struct page *page, unsigned int nr)
> +{
> +	int i;
> +	struct page_ext *page_ext;
> +	union codetag_ref *ref;
> +	struct alloc_tag *tag;
> +
> +	if (!mem_alloc_profiling_enabled())
> +		return;
> +
> +	page_ext = page_ext_get(page);
> +	if (unlikely(!page_ext))
> +		return;
> +
> +	ref = codetag_ref_from_page_ext(page_ext);
> +	if (!ref->ct)
> +		goto out;
> +
> +	tag = ct_to_alloc_tag(ref->ct);
> +	page_ext = page_ext_next(page_ext);
> +	for (i = 1; i < nr; i++) {
> +		/* Set new reference to point to the original tag */
> +		alloc_tag_ref_set(codetag_ref_from_page_ext(page_ext), tag);
> +		page_ext = page_ext_next(page_ext);
> +	}
> +out:
> +	page_ext_put(page_ext);
> +}
> +
>  #else /* CONFIG_MEM_ALLOC_PROFILING */
>  
>  static inline void pgalloc_tag_add(struct page *page, struct task_struct *task,
>  				   unsigned int order) {}
>  static inline void pgalloc_tag_sub(struct page *page, unsigned int order) {}
> +static inline void pgalloc_tag_split(struct page *page, unsigned int nr) {}
>  
>  #endif /* CONFIG_MEM_ALLOC_PROFILING */
>  
> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
> index 94c958f7ebb5..86daae671319 100644
> --- a/mm/huge_memory.c
> +++ b/mm/huge_memory.c
> @@ -38,6 +38,7 @@
>  #include <linux/sched/sysctl.h>
>  #include <linux/memory-tiers.h>
>  #include <linux/compat.h>
> +#include <linux/pgalloc_tag.h>
>  
>  #include <asm/tlb.h>
>  #include <asm/pgalloc.h>
> @@ -2899,6 +2900,7 @@ static void __split_huge_page(struct page *page, struct list_head *list,
>  	/* Caller disabled irqs, so they are still disabled here */
>  
>  	split_page_owner(head, nr);
> +	pgalloc_tag_split(head, nr);
>  
>  	/* See comment in __split_huge_page_tail() */
>  	if (PageAnon(head)) {
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 58c0e8b948a4..4bc5b4720fee 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -2621,6 +2621,7 @@ void split_page(struct page *page, unsigned int order)
>  	for (i = 1; i < (1 << order); i++)
>  		set_page_refcounted(page + i);
>  	split_page_owner(page, 1 << order);
> +	pgalloc_tag_split(page, 1 << order);
>  	split_page_memcg(page, 1 << order);
>  }
>  EXPORT_SYMBOL_GPL(split_page);
> @@ -4806,6 +4807,7 @@ static void *make_alloc_exact(unsigned long addr, unsigned int order,
>  		struct page *last = page + nr;
>  
>  		split_page_owner(page, 1 << order);
> +		pgalloc_tag_split(page, 1 << order);
>  		split_page_memcg(page, 1 << order);
>  		while (page < --last)
>  			set_page_refcounted(last);