Re: [PATCH] memcg: drop type MEM_CGROUP_CHARGE_TYPE_DROP

[Johannes Weiner <jweiner@redhat.com>]

On Wed, Dec 07, 2011 at 06:30:46PM +0800, Bob Liu wrote:
> uncharge will happen only when !page_mapped(page) no matter MEM_CGROUP_CHARGE_TYPE_DROP
> or MEM_CGROUP_CHARGE_TYPE_SWAPOUT when called from mem_cgroup_uncharge_swapcache().
> i think it's no difference, so drop it.
> 
> Signed-off-by: Bob Liu <lliubbo@gmail.com>
> ---
>  mm/memcontrol.c |    5 -----
>  1 files changed, 0 insertions(+), 5 deletions(-)
> 
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index 6aff93c..02a2988 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -339,7 +339,6 @@ enum charge_type {
>  	MEM_CGROUP_CHARGE_TYPE_SHMEM,	/* used by page migration of shmem */
>  	MEM_CGROUP_CHARGE_TYPE_FORCE,	/* used by force_empty */
>  	MEM_CGROUP_CHARGE_TYPE_SWAPOUT,	/* for accounting swapcache */
> -	MEM_CGROUP_CHARGE_TYPE_DROP,	/* a page was unused swap cache */
>  	NR_CHARGE_TYPE,
>  };
>  
> @@ -3000,7 +2999,6 @@ __mem_cgroup_uncharge_common(struct page *page, enum charge_type ctype)
>  
>  	switch (ctype) {
>  	case MEM_CGROUP_CHARGE_TYPE_MAPPED:
> -	case MEM_CGROUP_CHARGE_TYPE_DROP:
>  		/* See mem_cgroup_prepare_migration() */
>  		if (page_mapped(page) || PageCgroupMigration(pc))
>  			goto unlock_out;
> @@ -3121,9 +3119,6 @@ mem_cgroup_uncharge_swapcache(struct page *page, swp_entry_t ent, bool swapout)
>  	struct mem_cgroup *memcg;
>  	int ctype = MEM_CGROUP_CHARGE_TYPE_SWAPOUT;
>  
> -	if (!swapout) /* this was a swap cache but the swap is unused ! */
> -		ctype = MEM_CGROUP_CHARGE_TYPE_DROP;
> -

Pages are in swap cache for swapping in as well as for swapping out.
When a page is removed from swap cache and memory, the accounting
needs to know about the direction.  See the other checks against
TYPE_SWAPOUT.

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