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SubjectRe: [PATCH 1/2] memcg: remove MEMCG_NR_FILE_MAPPED
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On Fri, Jun 15 2012, Sha Zhengju wrote:

> While doing memcg page stat accounting, there's no need to use MEMCG_NR_FILE_MAPPED
> as an intermediate, we can use MEM_CGROUP_STAT_FILE_MAPPED directly.
>
> Signed-off-by: Sha Zhengju <handai.szj@taobao.com>
> ---
> include/linux/memcontrol.h | 22 ++++++++++++++++------
> mm/memcontrol.c | 25 +------------------------
> mm/rmap.c | 4 ++--
> 3 files changed, 19 insertions(+), 32 deletions(-)

I assume this patch is relative to v3.4.

> diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
> index f94efd2..a337c2e 100644
> --- a/include/linux/memcontrol.h
> +++ b/include/linux/memcontrol.h
> @@ -27,9 +27,19 @@ struct page_cgroup;
> struct page;
> struct mm_struct;
>
> -/* Stats that can be updated by kernel. */
> -enum mem_cgroup_page_stat_item {
> - MEMCG_NR_FILE_MAPPED, /* # of pages charged as file rss */
> +/*
> + * Statistics for memory cgroup.
> + */
> +enum mem_cgroup_stat_index {
> + /*
> + * For MEM_CONTAINER_TYPE_ALL, usage = pagecache + rss.
> + */
> + MEM_CGROUP_STAT_CACHE, /* # of pages charged as cache */
> + MEM_CGROUP_STAT_RSS, /* # of pages charged as anon rss */
> + MEM_CGROUP_STAT_FILE_MAPPED, /* # of pages charged as file rss */
> + MEM_CGROUP_STAT_SWAPOUT, /* # of pages, swapped out */
> + MEM_CGROUP_STAT_DATA, /* end of data requires synchronization */
> + MEM_CGROUP_STAT_NSTATS,
> };

This has unfortunate side effect of letting code outside of memcontrol.c
manipulate memcg internally managed statistics
(e.g. MEM_CGROUP_STAT_CACHE) with mem_cgroup_{dec,inc}_page_stat. I
think that your change is fine. The complexity and presumed performance
overhead of the extra layer of indirection was not worth it.

> struct mem_cgroup_reclaim_cookie {
> @@ -170,17 +180,17 @@ static inline void mem_cgroup_end_update_page_stat(struct page *page,
> }
>
> void mem_cgroup_update_page_stat(struct page *page,
> - enum mem_cgroup_page_stat_item idx,
> + enum mem_cgroup_stat_index idx,
> int val);
>
> static inline void mem_cgroup_inc_page_stat(struct page *page,
> - enum mem_cgroup_page_stat_item idx)
> + enum mem_cgroup_stat_index idx)
> {
> mem_cgroup_update_page_stat(page, idx, 1);
> }
>
> static inline void mem_cgroup_dec_page_stat(struct page *page,
> - enum mem_cgroup_page_stat_item idx)
> + enum mem_cgroup_stat_index idx)
> {
> mem_cgroup_update_page_stat(page, idx, -1);
> }

You missed two more uses of enum mem_cgroup_page_stat_item in
memcontrol.h.

diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
index a337c2e..08475b9 100644
--- a/include/linux/memcontrol.h
+++ b/include/linux/memcontrol.h
@@ -390,12 +390,12 @@ static inline void mem_cgroup_end_update_page_stat(struct page *page,
}

static inline void mem_cgroup_inc_page_stat(struct page *page,
- enum mem_cgroup_page_stat_item idx)
+ enum mem_cgroup_stat_index idx)
{
}

static inline void mem_cgroup_dec_page_stat(struct page *page,
- enum mem_cgroup_page_stat_item idx)
+ enum mem_cgroup_stat_index idx)
{
}

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