On Wed, Mar 28, 2012 at 3:51 AM, KAMEZAWA Hiroyuki
<kamezawa.hiroyu@xxxxxxxxxxxxxx> wrote:
> Consolidate a code for setting pc->mem_cgroup and USED bit which requires smp_wmb().
> And remove a macro PCGF_NOCOPY_AT_SPLIT which isn't helpful to read code, now.
>
> Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx>
> ---
> include/linux/page_cgroup.h | 18 ++++++++++++++++++
> mm/memcontrol.c | 18 ++++--------------
> 2 files changed, 22 insertions(+), 14 deletions(-)
>
> diff --git a/include/linux/page_cgroup.h b/include/linux/page_cgroup.h
> index 92768cb..2707809 100644
> --- a/include/linux/page_cgroup.h
> +++ b/include/linux/page_cgroup.h
> @@ -1,6 +1,8 @@
> #ifndef __LINUX_PAGE_CGROUP_H
> #define __LINUX_PAGE_CGROUP_H
>
> +#include <linux/smp.h>
> +
> enum {
> /* flags for mem_cgroup */
> PCG_LOCK, /* Lock for pc->mem_cgroup and following bits. */
> @@ -94,6 +96,22 @@ pc_set_mem_cgroup(struct page_cgroup *pc, struct mem_cgroup *memcg)
> pc->mem_cgroup = memcg;
> }
>
> +static inline void
> +pc_set_mem_cgroup_and_flags(struct page_cgroup *pc, struct mem_cgroup *memcg,
> + unsigned long flags)
> +{
> + pc->mem_cgroup = memcg;
> + /*
> + * We access a page_cgroup asynchronously without lock_page_cgroup().
> + * Especially when a page_cgroup is taken from a page, pc's mem_cgroup
> + * is accessed after testing USED bit. To make pc's mem_cgroup visible
> + * before USED bit, we need memory barrier here.
> + * See mem_cgroup_add_lru_list(), etc.
> + */
> + smp_wmb();
> + pc->flags = flags;
> +}
> +
> #else /* CONFIG_CGROUP_MEM_RES_CTLR */
> struct page_cgroup;
>
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index 8077460..d366b60 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -2511,16 +2511,7 @@ static void __mem_cgroup_commit_charge(struct mem_cgroup *memcg,
> }
> }
>
> - pc_set_mem_cgroup(pc, memcg);
> - /*
> - * We access a page_cgroup asynchronously without lock_page_cgroup().
> - * Especially when a page_cgroup is taken from a page, pc's mem_cgroup
> - * is accessed after testing USED bit. To make pc's mem_cgroup visible
> - * before USED bit, we need memory barrier here.
> - * See mem_cgroup_add_lru_list(), etc.
> - */
> - smp_wmb();
> - SetPageCgroupUsed(pc);
I might be confused. We removed this SetPageCgroupUsed() but not
adding it back elsewhere ?
--Ying
> + pc_set_mem_cgroup_and_flags(pc, memcg, BIT(PCG_USED) | BIT(PCG_LOCK));
>
> if (lrucare) {
> if (was_on_lru) {
> @@ -2549,7 +2540,6 @@ static void __mem_cgroup_commit_charge(struct mem_cgroup *memcg,
>
> #ifdef CONFIG_TRANSPARENT_HUGEPAGE
>
> -#define PCGF_NOCOPY_AT_SPLIT ((1 << PCG_LOCK) | (1 << PCG_MIGRATION))
> /*
> * Because tail pages are not marked as "used", set it. We're under
> * zone->lru_lock, 'splitting on pmd' and compound_lock.
> @@ -2565,11 +2555,11 @@ void mem_cgroup_split_huge_fixup(struct page *head)
>
> if (mem_cgroup_disabled())
> return;
> + if (!PageCgroupUsed(head_pc))
> + return;
> for (i = 1; i < HPAGE_PMD_NR; i++) {
> pc = head_pc + i;
> - pc_set_mem_cgroup(pc, memcg);
> - smp_wmb();/* see __commit_charge() */
> - pc->flags = head_pc->flags & ~PCGF_NOCOPY_AT_SPLIT;
> + pc_set_mem_cgroup_and_flags(pc, memcg, BIT(PCG_USED));
> }
> }
> #endif /* CONFIG_TRANSPARENT_HUGEPAGE */
> --
> 1.7.4.1
>
>
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