[PATCH] mm/memcg: update page struct member in comments

[PATCH] mm/memcg: update page struct member in comments

[Alex Shi]

The page->mem_cgroup member is replaced by memcg_data, and add a helper
page_memcg() for it. Need to update comments to avoid confusing.

Signed-off-by: Alex Shi <alex.shi@linux.alibaba.com>
Cc: Johannes Weiner <hannes@cmpxchg.org> 
Cc: Michal Hocko <mhocko@kernel.org> 
Cc: Vladimir Davydov <vdavydov.dev@gmail.com> 
Cc: Andrew Morton <akpm@linux-foundation.org> 
Cc: cgroups@vger.kernel.org 
Cc: linux-mm@kvack.org 
Cc: linux-kernel@vger.kernel.org 
---
 mm/memcontrol.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index b2aa3b73ab82..8a8debea34fc 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -1310,7 +1310,7 @@ int mem_cgroup_scan_tasks(struct mem_cgroup *memcg,
  * @page: the page
  * @pgdat: pgdat of the page
  *
- * This function relies on page->mem_cgroup being stable - see the
+ * This function relies on page_memcg(page) being stable - see the
  * access rules in commit_charge().
  */
 struct lruvec *mem_cgroup_page_lruvec(struct page *page, struct pglist_data *pgdat)
@@ -2862,7 +2862,7 @@ static void commit_charge(struct page *page, struct mem_cgroup *memcg)
 {
 	VM_BUG_ON_PAGE(page_memcg(page), page);
 	/*
-	 * Any of the following ensures page->mem_cgroup stability:
+	 * Any of the following ensures page_memcg(page) stability:
 	 *
 	 * - the page lock
 	 * - LRU isolation
-- 
1.8.3.1

Re: [PATCH] mm/memcg: update page struct member in comments

[Ira Weiny]

On Fri, Nov 06, 2020 at 07:33:33PM +0800, Alex Shi wrote:
> The page->mem_cgroup member is replaced by memcg_data, and add a helper
> page_memcg() for it. Need to update comments to avoid confusing.

I'm not an expert in this code but IMO the pointer manipulation of
page->mem_cgroup could be thought of as local to the code in mm/memcontrol.c.
As such the detail of the member of the page struct that the code depends on is
a valuable part of the comment.  Having to look at page_memcg() to find out
this information is kind of annoying.

Ira

> 
> Signed-off-by: Alex Shi <alex.shi@linux.alibaba.com>
> Cc: Johannes Weiner <hannes@cmpxchg.org> 
> Cc: Michal Hocko <mhocko@kernel.org> 
> Cc: Vladimir Davydov <vdavydov.dev@gmail.com> 
> Cc: Andrew Morton <akpm@linux-foundation.org> 
> Cc: cgroups@vger.kernel.org 
> Cc: linux-mm@kvack.org 
> Cc: linux-kernel@vger.kernel.org 
> ---
>  mm/memcontrol.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index b2aa3b73ab82..8a8debea34fc 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -1310,7 +1310,7 @@ int mem_cgroup_scan_tasks(struct mem_cgroup *memcg,
>   * @page: the page
>   * @pgdat: pgdat of the page
>   *
> - * This function relies on page->mem_cgroup being stable - see the
> + * This function relies on page_memcg(page) being stable - see the
>   * access rules in commit_charge().
>   */
>  struct lruvec *mem_cgroup_page_lruvec(struct page *page, struct pglist_data *pgdat)
> @@ -2862,7 +2862,7 @@ static void commit_charge(struct page *page, struct mem_cgroup *memcg)
>  {
>  	VM_BUG_ON_PAGE(page_memcg(page), page);
>  	/*
> -	 * Any of the following ensures page->mem_cgroup stability:
> +	 * Any of the following ensures page_memcg(page) stability:
>  	 *
>  	 * - the page lock
>  	 * - LRU isolation
> -- 
> 1.8.3.1
> 

Re: [PATCH] mm/memcg: update page struct member in comments

[Roman Gushchin]

On Fri, Nov 06, 2020 at 07:33:33PM +0800, Alex Shi wrote:
> The page->mem_cgroup member is replaced by memcg_data, and add a helper
> page_memcg() for it. Need to update comments to avoid confusing.

Hi Alex,

thank you for bringing it in!
I definitely missed those.

> 
> Signed-off-by: Alex Shi <alex.shi@linux.alibaba.com>
> Cc: Johannes Weiner <hannes@cmpxchg.org> 
> Cc: Michal Hocko <mhocko@kernel.org> 
> Cc: Vladimir Davydov <vdavydov.dev@gmail.com> 
> Cc: Andrew Morton <akpm@linux-foundation.org> 
> Cc: cgroups@vger.kernel.org 
> Cc: linux-mm@kvack.org 
> Cc: linux-kernel@vger.kernel.org 
> ---
>  mm/memcontrol.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index b2aa3b73ab82..8a8debea34fc 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -1310,7 +1310,7 @@ int mem_cgroup_scan_tasks(struct mem_cgroup *memcg,
>   * @page: the page
>   * @pgdat: pgdat of the page
>   *
> - * This function relies on page->mem_cgroup being stable - see the
> + * This function relies on page_memcg(page) being stable - see the
>   * access rules in commit_charge().

There are "page and memcg binding" and "page's memcg" used in similar cases,
I think it's more obvious than "page_memcg(page) being stable".

Maybe it helps to address Ira's comment.

Anyway, please feel free to add:
Acked-by: Roman Gushchin <guro@fb.com>

Thanks!

Re: [PATCH] mm/memcg: update page struct member in comments

[Alex Shi]

在 2020/11/7 上午4:51, Roman Gushchin 写道:
> There are "page and memcg binding" and "page's memcg" used in similar cases,
> I think it's more obvious than "page_memcg(page) being stable".
> 
> Maybe it helps to address Ira's comment.
> 
> Anyway, please feel free to add:
> Acked-by: Roman Gushchin <guro@fb.com>
> 
> Thanks!

Thanks a lot! Roman.
here is the updated patch with your suggestion and ack.


From 0db2bd8f3833ec5e58c6978f771b05e4902e5156 Mon Sep 17 00:00:00 2001
From: Alex Shi <alex.shi@linux.alibaba.com>
Date: Fri, 6 Nov 2020 19:33:33 +0800
Subject: [PATCH v2] mm/memcg: update page struct member in comments

The page->mem_cgroup member is replaced by memcg_data, and add a helper
page_memcg() for it. Need to update comments to avoid confusing.

Signed-off-by: Alex Shi <alex.shi@linux.alibaba.com>
Acked-by: Roman Gushchin <guro@fb.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Vladimir Davydov <vdavydov.dev@gmail.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: cgroups@vger.kernel.org
Cc: linux-mm@kvack.org
Cc: linux-kernel@vger.kernel.org
---
 mm/memcontrol.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 7657f16cf992..b6560ab1adc4 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -1330,7 +1330,7 @@ void lruvec_memcg_debug(struct lruvec *lruvec, struct page *page)
  * @page: the page
  * @pgdat: pgdat of the page
  *
- * This function relies on page->mem_cgroup being stable - see the
+ * This function relies on page's memcg being stable - see the
  * access rules in commit_charge().
  */
 struct lruvec *mem_cgroup_page_lruvec(struct page *page, struct pglist_data *pgdat)
@@ -2942,7 +2942,7 @@ static void commit_charge(struct page *page, struct mem_cgroup *memcg)
 {
 	VM_BUG_ON_PAGE(page_memcg(page), page);
 	/*
-	 * Any of the following ensures page->mem_cgroup stability:
+	 * Any of the following ensures page's memcg stability:
 	 *
 	 * - the page lock
 	 * - LRU isolation
-- 
1.8.3.1