Date:   Fri, 3 Mar 2023 07:22:56 -0800
From:   Zach O'Keefe <zokeefe@google.com>
To:     Peter Xu <peterx@redhat.com>
Cc:     linux-mm@kvack.org, linux-kernel@vger.kernel.org,
        David Stevens <stevensd@chromium.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Yang Shi <shy828301@gmail.com>,
        Johannes Weiner <hannes@cmpxchg.org>
Subject: Re: [PATCH] mm/khugepaged: Cleanup memcg uncharge for failure path
Message-ID: <20230303152256.a5z3wc2v6wri5ijy@google.com>
References: <20230303151218.311015-1-peterx@redhat.com>
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In-Reply-To: <20230303151218.311015-1-peterx@redhat.com>
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Thanks Peter!

On Mar 03 10:12, Peter Xu wrote:
> Explicit memcg uncharging is not needed when the memcg accounting has the
> same lifespan of the page/folio.  That becomes the case for khugepaged
> after Yang & Zach's recent rework so the hpage will be allocated for each
> collapse rather than being cached.
> 
> Cleanup the explicit memcg uncharge in khugepaged failure path and leave
> that for put_page().
> 
> Suggested-by: Zach O'Keefe <zokeefe@google.com>
> Signed-off-by: Peter Xu <peterx@redhat.com>

Reviewed-by: Zach O'Keefe <zokeefe@google.com>

> ---
>  mm/khugepaged.c | 8 ++------
>  1 file changed, 2 insertions(+), 6 deletions(-)
> 
> diff --git a/mm/khugepaged.c b/mm/khugepaged.c
> index 941d1c7ea910..dd5a7d9bc593 100644
> --- a/mm/khugepaged.c
> +++ b/mm/khugepaged.c
> @@ -1230,10 +1230,8 @@ static int collapse_huge_page(struct mm_struct *mm, unsigned long address,
>  out_up_write:
>  	mmap_write_unlock(mm);
>  out_nolock:
> -	if (hpage) {
> -		mem_cgroup_uncharge(page_folio(hpage));
> +	if (hpage)
>  		put_page(hpage);
> -	}
>  	trace_mm_collapse_huge_page(mm, result == SCAN_SUCCEED, result);
>  	return result;
>  }
> @@ -2250,10 +2248,8 @@ static int collapse_file(struct mm_struct *mm, unsigned long addr,
>  		unlock_page(hpage);
>  out:
>  	VM_BUG_ON(!list_empty(&pagelist));
> -	if (hpage) {
> -		mem_cgroup_uncharge(page_folio(hpage));
> +	if (hpage)
>  		put_page(hpage);
> -	}
>  
>  	trace_mm_khugepaged_collapse_file(mm, hpage, index, is_shmem, addr, file, nr, result);
>  	return result;
> -- 
> 2.39.1
>