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    Subject[RFC][PATCH 2/6] memcg: add pc_set_mem_cgroup_and_flags()
    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);
    + 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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