memcg: dirty pages accounting and limiting infrastructure
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From: Greg Thelen on 18 Mar 2010 03:00 I have a proposed change to "[PATCH -mmotm 4/5] memcg: dirty pages accounting and limiting infrastructure" v6. The change is small and I am presenting it as a git patch (below) to be applied after 4/5 v6 has been applied. The change is fairly simple. An alternative would be to reject my patch (below) and enhance get_vm_dirty_param() to loop for consistenty in all cases. ---patch snip here, rest of email is git patch of 4/5 v6 --- Removed unneeded looping from get_vm_dirty_param(). The only caller of get_vm_dirty_param() gracefully handles inconsistent values, so there is no need for get_vm_dirty_param() to loop to ensure consistency. The previous looping was inconsistent because it did not loop for the case where memory cgroups were disabled. Signed-off-by: Greg Thelen <gthelen(a)google.com> --- mm/memcontrol.c | 28 ++++++++++++---------------- 1 files changed, 12 insertions(+), 16 deletions(-) diff --git a/mm/memcontrol.c b/mm/memcontrol.c index 4d00c0f..990a907 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -1081,6 +1081,10 @@ static void __mem_cgroup_get_dirty_param(struct vm_dirty_param *param, * The function fills @param with the current memcg dirty memory settings. If * memory cgroup is disabled or in case of error the structure is filled with * the global dirty memory settings. + * + * Because global and memcg vm_dirty_param are not protected, inconsistent + * values may be returned. If consistent values are required, then the caller + * should call this routine until dirty_param_is_valid() returns true. */ void get_vm_dirty_param(struct vm_dirty_param *param) { @@ -1090,28 +1094,20 @@ void get_vm_dirty_param(struct vm_dirty_param *param) get_global_vm_dirty_param(param); return; } + /* * It's possible that "current" may be moved to other cgroup while we * access cgroup. But precise check is meaningless because the task can * be moved after our access and writeback tends to take long time. * At least, "memcg" will not be freed under rcu_read_lock(). */ - while (1) { - rcu_read_lock(); - memcg = mem_cgroup_from_task(current); - if (likely(memcg)) - __mem_cgroup_get_dirty_param(param, memcg); - else - get_global_vm_dirty_param(param); - rcu_read_unlock(); - /* - * Since global and memcg vm_dirty_param are not protected we - * try to speculatively read them and retry if we get - * inconsistent values. - */ - if (likely(dirty_param_is_valid(param))) - break; - } + rcu_read_lock(); + memcg = mem_cgroup_from_task(current); + if (likely(memcg)) + __mem_cgroup_get_dirty_param(param, memcg); + else + get_global_vm_dirty_param(param); + rcu_read_unlock(); } /* -- 1.7.0.1 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo(a)vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/ |