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    SubjectRe: [RFC][PATCH 2/6] memcg: add pc_set_mem_cgroup_and_flags()
    (2012/04/18 6:17), Ying Han wrote:

    > On Wed, Mar 28, 2012 at 3:51 AM, KAMEZAWA Hiroyuki
    > <kamezawa.hiroyu@jp.fujitsu.com> 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@jp.fujitsu.com>
    >> ---
    >> 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));


    Added here. This sets

    | memcg pointer | Used | Locked |


    Thanks,
    -Kame






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