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    SubjectRe: [PATCH 1/2] memcg: dirty pages accounting and limiting infrastructure
    On Sun, Feb 21, 2010 at 11:17:01PM +0100, Andrea Righi wrote:
    > On Sun, Feb 21, 2010 at 01:28:35PM -0800, David Rientjes wrote:
    >
    > [snip]
    >
    > > > +static struct mem_cgroup *get_mem_cgroup_from_page(struct page *page)
    > > > +{
    > > > + struct page_cgroup *pc;
    > > > + struct mem_cgroup *mem = NULL;
    > > > +
    > > > + pc = lookup_page_cgroup(page);
    > > > + if (unlikely(!pc))
    > > > + return NULL;
    > > > + lock_page_cgroup(pc);
    > > > + if (PageCgroupUsed(pc)) {
    > > > + mem = pc->mem_cgroup;
    > > > + if (mem)
    > > > + css_get(&mem->css);
    > > > + }
    > > > + unlock_page_cgroup(pc);
    > > > + return mem;
    > > > +}
    > >
    > > Is it possible to merge this with try_get_mem_cgroup_from_page()?
    >
    > Agreed.
    >
    > >
    > > > +
    > > > +void mem_cgroup_charge_dirty(struct page *page,
    > > > + enum zone_stat_item idx, int charge)
    > > > +{
    > > > + struct mem_cgroup *mem;
    > > > + struct mem_cgroup_stat_cpu *cpustat;
    > > > + unsigned long flags;
    > > > + int cpu;
    > > > +
    > > > + if (mem_cgroup_disabled())
    > > > + return;
    > > > + /* Translate the zone_stat_item into a mem_cgroup_stat_index */
    > > > + switch (idx) {
    > > > + case NR_FILE_DIRTY:
    > > > + idx = MEM_CGROUP_STAT_FILE_DIRTY;
    > > > + break;
    > > > + case NR_WRITEBACK:
    > > > + idx = MEM_CGROUP_STAT_WRITEBACK;
    > > > + break;
    > > > + case NR_WRITEBACK_TEMP:
    > > > + idx = MEM_CGROUP_STAT_WRITEBACK_TEMP;
    > > > + break;
    > > > + case NR_UNSTABLE_NFS:
    > > > + idx = MEM_CGROUP_STAT_UNSTABLE_NFS;
    > > > + break;
    > > > + default:
    > > > + return;
    > >
    > > WARN()? We don't want to silently leak counters.
    >
    > Agreed.
    >
    > >
    > > > + }
    > > > + /* Charge the memory cgroup statistics */
    > > > + mem = get_mem_cgroup_from_page(page);
    > > > + if (!mem) {
    > > > + mem = root_mem_cgroup;
    > > > + css_get(&mem->css);
    > > > + }
    > >
    > > get_mem_cgroup_from_page() should probably handle the root_mem_cgroup case
    > > and return a reference from it.
    >
    > Right. But I'd prefer to use try_get_mem_cgroup_from_page() without
    > changing the behaviour of this function.
    >
    > >
    > > > +
    > > > + local_irq_save(flags);
    > > > + cpu = get_cpu();
    > > > + cpustat = &mem->stat.cpustat[cpu];
    > > > + __mem_cgroup_stat_add_safe(cpustat, idx, charge);
    > >
    > > get_cpu()? Preemption is already disabled, just use smp_processor_id().
    >
    > mmmh... actually, we can just copy the code from
    > mem_cgroup_charge_statistics(), so local_irq_save/restore are not
    > necessarily needed and we can just use get_cpu()/put_cpu().
    >
    > > > + put_cpu();
    > > > + local_irq_restore(flags);
    > > > + css_put(&mem->css);
    > > > +}
    > > > +
    > > > static unsigned long mem_cgroup_get_local_zonestat(struct mem_cgroup *mem,
    > > > enum lru_list idx)
    > > > {
    > > > @@ -992,6 +1061,97 @@ static unsigned int get_swappiness(struct mem_cgroup *memcg)
    > > > return swappiness;
    > > > }
    > > >
    > > > +static unsigned long get_dirty_bytes(struct mem_cgroup *memcg)
    > > > +{
    > > > + struct cgroup *cgrp = memcg->css.cgroup;
    > > > + unsigned long dirty_bytes;
    > > > +
    > > > + /* root ? */
    > > > + if (cgrp->parent == NULL)
    > > > + return vm_dirty_bytes;
    > > > +
    > > > + spin_lock(&memcg->reclaim_param_lock);
    > > > + dirty_bytes = memcg->dirty_bytes;
    > > > + spin_unlock(&memcg->reclaim_param_lock);
    > > > +
    > > > + return dirty_bytes;
    > > > +}
    > > > +
    > > > +unsigned long mem_cgroup_dirty_bytes(void)
    > > > +{
    > > > + struct mem_cgroup *memcg;
    > > > + unsigned long dirty_bytes;
    > > > +
    > > > + if (mem_cgroup_disabled())
    > > > + return vm_dirty_bytes;
    > > > +
    > > > + rcu_read_lock();
    > > > + memcg = mem_cgroup_from_task(current);
    > > > + if (memcg == NULL)
    > > > + dirty_bytes = vm_dirty_bytes;
    > > > + else
    > > > + dirty_bytes = get_dirty_bytes(memcg);
    > > > + rcu_read_unlock();
    > >
    > > The rcu_read_lock() isn't protecting anything here.
    >
    > Right!

    Are we not protecting "memcg" pointer using rcu here?

    Thanks
    Vivek


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