On Wed, Apr 11, 2012 at 03:00:06PM -0700, Ying Han wrote:
> Add the filter function should_reclaim_mem_cgroup() under the common function
> shrink_zone(). The later one is being called both from per-memcg reclaim as
> well as global reclaim.
>
> Today the softlimit takes effect only under global memory pressure. The memcgs
> get free run above their softlimit until there is a global memory contention.
> This patch doesn't change the semantics.
>
> Under the global reclaim, we skip reclaiming from a memcg under its softlimit.
> To prevent reclaim from trying too hard on hitting memcgs (above softlimit) w/
> only hard-to-reclaim pages, the reclaim proirity is used to skip the softlimit
> check. This is a trade-off of system performance and resource isolation.
>
> Signed-off-by: Ying Han <yinghan@xxxxxxxxxx>
> ---
> include/linux/memcontrol.h | 7 +++++++
> mm/memcontrol.c | 10 +++++++++-
> mm/vmscan.c | 25 ++++++++++++++++++++++++-
> 3 files changed, 40 insertions(+), 2 deletions(-)
>
> diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
> index db71193..3d14f90 100644
> --- a/include/linux/memcontrol.h
> +++ b/include/linux/memcontrol.h
> @@ -110,6 +110,8 @@ struct mem_cgroup *mem_cgroup_iter(struct mem_cgroup *,
> struct mem_cgroup_reclaim_cookie *);
> void mem_cgroup_iter_break(struct mem_cgroup *, struct mem_cgroup *);
>
> +bool mem_cgroup_soft_limit_exceeded(struct mem_cgroup *);
> +
> /*
> * For memory reclaim.
> */
> @@ -295,6 +297,11 @@ static inline void mem_cgroup_iter_break(struct mem_cgroup *root,
> {
> }
>
> +static inline bool mem_cgroup_soft_limit_exceeded(struct mem_cgroup *mem)
> +{
> + return true;
> +}
> +
> static inline int mem_cgroup_get_reclaim_priority(struct mem_cgroup *memcg)
> {
> return 0;
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index 9a64093..cffcded 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -358,12 +358,12 @@ enum charge_type {
> static void mem_cgroup_get(struct mem_cgroup *memcg);
> static void mem_cgroup_put(struct mem_cgroup *memcg);
>
> +static bool mem_cgroup_is_root(struct mem_cgroup *memcg);
> /* Writing them here to avoid exposing memcg's inner layout */
> #ifdef CONFIG_CGROUP_MEM_RES_CTLR_KMEM
> #include <net/sock.h>
> #include <net/ip.h>
>
> -static bool mem_cgroup_is_root(struct mem_cgroup *memcg);
The prototype is hardly shorter than the friggin function itself!
I'll send a patch to remove this thing completely, doing memcg ==
root_mem_cgroup should be pretty obvious without a helper function.
> @@ -2133,6 +2133,27 @@ restart:
> throttle_vm_writeout(sc->gfp_mask);
> }
>
> +static bool should_reclaim_mem_cgroup(struct mem_cgroup *target_mem_cgroup,
> + struct mem_cgroup *memcg,
> + int priority)
> +{
> + /* Reclaim from mem_cgroup if any of these conditions are met:
> + * - This is a global reclaim
> + * - reclaim priority is higher than DEF_PRIORITY - 3
> + * - mem_cgroup exceeds its soft limit
> + *
> + * The priority check is a balance of how hard to preserve the pages
> + * under softlimit. If the memcgs of the zone having trouble to reclaim
> + * pages above their softlimit, we have to reclaim under softlimit
> + * instead of burning more cpu cycles.
> + */
> + if (target_mem_cgroup || priority <= DEF_PRIORITY - 3 ||
> + mem_cgroup_soft_limit_exceeded(memcg))
> + return true;
The comment is contradicting the code: global reclaim does not scan
unconditionally, hard limit reclaim does. Global reclaim scans only
if the memcg is above soft limit or if the priority level dropped
sufficiently.
I suppose it's the comment that's wrong, not the code.
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