linux-kernel - Re: [PATCH v2] fs/proc/page: Refactoring to reduce code duplication.

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Message-ID: <a43ff37d-497c-4508-b6e5-667e060908cc@redhat.com>
Date: Mon, 17 Mar 2025 11:24:02 +0100
From: David Hildenbrand <david@...hat.com>
To: Liu Ye <liuyerd@....com>, akpm@...ux-foundation.org
Cc: willy@...radead.org, ran.xiaokai@....com.cn, dan.carpenter@...aro.org,
 linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
 Liu Ye <liuye@...inos.cn>
Subject: Re: [PATCH v2] fs/proc/page: Refactoring to reduce code duplication.

On 17.03.25 11:07, Liu Ye wrote:
> From: Liu Ye <liuye@...inos.cn>
> 
> The function kpageflags_read and kpagecgroup_read is quite similar
> to kpagecount_read. Consider refactoring common code into a helper
> function to reduce code duplication.
> 
> Signed-off-by: Liu Ye <liuye@...inos.cn>
> 
> ---
> V2 : Use an enumeration to indicate the operation to be performed
> to avoid passing functions.
> ---
> ---
>   fs/proc/page.c | 166 +++++++++++++++++--------------------------------
>   1 file changed, 58 insertions(+), 108 deletions(-)
> 
> diff --git a/fs/proc/page.c b/fs/proc/page.c
> index a55f5acefa97..66f454330a87 100644
> --- a/fs/proc/page.c
> +++ b/fs/proc/page.c
> @@ -22,6 +22,14 @@
>   #define KPMMASK (KPMSIZE - 1)
>   #define KPMBITS (KPMSIZE * BITS_PER_BYTE)
>   
> +enum kpage_operation {
> +	KPAGE_FLAGS,
> +	KPAGE_COUNT,
> +#ifdef CONFIG_MEMCG
> +	KPAGE_CGROUP,
> +#endif
> +};
> +
>   static inline unsigned long get_max_dump_pfn(void)
>   {
>   #ifdef CONFIG_SPARSEMEM
> @@ -37,19 +45,17 @@ static inline unsigned long get_max_dump_pfn(void)
>   #endif
>   }
>   
> -/* /proc/kpagecount - an array exposing page mapcounts
> - *
> - * Each entry is a u64 representing the corresponding
> - * physical page mapcount.
> - */
> -static ssize_t kpagecount_read(struct file *file, char __user *buf,
> -			     size_t count, loff_t *ppos)
> +static ssize_t kpage_read(struct file *file, char __user *buf,
> +		size_t count, loff_t *ppos,
> +		enum kpage_operation op)
>   {
>   	const unsigned long max_dump_pfn = get_max_dump_pfn();
>   	u64 __user *out = (u64 __user *)buf;
> +	struct page *ppage;
>   	unsigned long src = *ppos;
>   	unsigned long pfn;
>   	ssize_t ret = 0;
> +	u64 info;
>   
>   	pfn = src / KPMSIZE;
>   	if (src & KPMMASK || count & KPMMASK)
> @@ -59,19 +65,29 @@ static ssize_t kpagecount_read(struct file *file, char __user *buf,
>   	count = min_t(unsigned long, count, (max_dump_pfn * KPMSIZE) - src);
>   
>   	while (count > 0) {
> -		struct page *page;
> -		u64 mapcount = 0;
> -
> -		/*
> -		 * TODO: ZONE_DEVICE support requires to identify
> -		 * memmaps that were actually initialized.
> -		 */
> -		page = pfn_to_online_page(pfn);
> -		if (page)
> -			mapcount = folio_precise_page_mapcount(page_folio(page),
> -							       page);
> -
> -		if (put_user(mapcount, out)) {
> +		ppage = pfn_to_online_page(pfn);
> +
> +		if (ppage) {
> +			switch (op) {
> +			case KPAGE_FLAGS:
> +				info = stable_page_flags(ppage);
> +				break;
> +			case KPAGE_COUNT:
> +				info = folio_precise_page_mapcount(page_folio(ppage), ppage);
> +				break;
> +#ifdef CONFIG_MEMCG
> +			case KPAGE_CGROUP:
> +				info = page_cgroup_ino(ppage);
> +				break;
> +#endif

In general, LGTM.

I do wonder if we should just get rid of the two "#ifdef CONFIG_MEMCG" by adding
a stub for page_cgroup_ino().

diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
index 57664e2a8fb7b..24248f4dcc971 100644
--- a/include/linux/memcontrol.h
+++ b/include/linux/memcontrol.h
@@ -1788,6 +1788,11 @@ static inline void count_objcg_events(struct obj_cgroup *objcg,
  {
  }
  
+static inline ino_t page_cgroup_ino(struct page *page)
+{
+       return 0;
+}
+
  #endif /* CONFIG_MEMCG */
  
  #if defined(CONFIG_MEMCG) && defined(CONFIG_ZSWAP)


-- 
Cheers,

David / dhildenb