linux-kernel - Re: [PATCH 2/3] mm: rmap: remove lock_page

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Date:   Tue, 6 Dec 2022 17:52:30 -0800 (PST)
From:   Hugh Dickins <hughd@...gle.com>
To:     Johannes Weiner <hannes@...xchg.org>
cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Hugh Dickins <hughd@...gle.com>,
        Shakeel Butt <shakeelb@...gle.com>,
        Michal Hocko <mhocko@...e.com>, linux-mm@...ck.org,
        cgroups@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/3] mm: rmap: remove lock_page_memcg()

On Tue, 6 Dec 2022, Johannes Weiner wrote:

> The previous patch made sure charge moving only touches pages for
> which page_mapped() is stable. lock_page_memcg() is no longer needed.
> 
> Signed-off-by: Johannes Weiner <hannes@...xchg.org>

Acked-by: Hugh Dickins <hughd@...gle.com>

> ---
>  mm/rmap.c | 26 ++++++++------------------
>  1 file changed, 8 insertions(+), 18 deletions(-)
> 
> diff --git a/mm/rmap.c b/mm/rmap.c
> index b616870a09be..32e48b1c5847 100644
> --- a/mm/rmap.c
> +++ b/mm/rmap.c
> @@ -1222,9 +1222,6 @@ void page_add_anon_rmap(struct page *page,
>  	bool compound = flags & RMAP_COMPOUND;
>  	bool first = true;
>  
> -	if (unlikely(PageKsm(page)))
> -		lock_page_memcg(page);
> -
>  	/* Is page being mapped by PTE? Is this its first map to be added? */
>  	if (likely(!compound)) {
>  		first = atomic_inc_and_test(&page->_mapcount);
> @@ -1262,15 +1259,14 @@ void page_add_anon_rmap(struct page *page,
>  	if (nr)
>  		__mod_lruvec_page_state(page, NR_ANON_MAPPED, nr);
>  
> -	if (unlikely(PageKsm(page)))
> -		unlock_page_memcg(page);
> -
> -	/* address might be in next vma when migration races vma_adjust */
> -	else if (first)
> -		__page_set_anon_rmap(page, vma, address,
> -				     !!(flags & RMAP_EXCLUSIVE));
> -	else
> -		__page_check_anon_rmap(page, vma, address);
> +	if (likely(!PageKsm(page))) {
> +		/* address might be in next vma when migration races vma_adjust */
> +		if (first)
> +			__page_set_anon_rmap(page, vma, address,
> +					     !!(flags & RMAP_EXCLUSIVE));
> +		else
> +			__page_check_anon_rmap(page, vma, address);
> +	}
>  
>  	mlock_vma_page(page, vma, compound);
>  }
> @@ -1329,7 +1325,6 @@ void page_add_file_rmap(struct page *page,
>  	bool first;
>  
>  	VM_BUG_ON_PAGE(compound && !PageTransHuge(page), page);
> -	lock_page_memcg(page);
>  
>  	/* Is page being mapped by PTE? Is this its first map to be added? */
>  	if (likely(!compound)) {
> @@ -1365,7 +1360,6 @@ void page_add_file_rmap(struct page *page,
>  			NR_SHMEM_PMDMAPPED : NR_FILE_PMDMAPPED, nr_pmdmapped);
>  	if (nr)
>  		__mod_lruvec_page_state(page, NR_FILE_MAPPED, nr);
> -	unlock_page_memcg(page);
>  
>  	mlock_vma_page(page, vma, compound);
>  }
> @@ -1394,8 +1388,6 @@ void page_remove_rmap(struct page *page,
>  		return;
>  	}
>  
> -	lock_page_memcg(page);
> -
>  	/* Is page being unmapped by PTE? Is this its last map to be removed? */
>  	if (likely(!compound)) {
>  		last = atomic_add_negative(-1, &page->_mapcount);
> @@ -1451,8 +1443,6 @@ void page_remove_rmap(struct page *page,
>  	 * and remember that it's only reliable while mapped.
>  	 */
>  
> -	unlock_page_memcg(page);
> -
>  	munlock_vma_page(page, vma, compound);
>  }
>  
> -- 
> 2.38.1
> 
>