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    SubjectRe: [PATCH -mmotm 3/4] memcg: dirty pages accounting and limiting infrastructure
    On Fri, 5 Mar 2010 10:12:34 +0900
    Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp> wrote:

    > On Thu, 4 Mar 2010 11:40:14 +0100, Andrea Righi <arighi@develer.com> wrote:
    > > Infrastructure to account dirty pages per cgroup and add dirty limit
    > > static int mem_cgroup_count_children_cb(struct mem_cgroup *mem, void *data)
    > > {
    > > int *val = data;
    > > @@ -1275,34 +1423,70 @@ static void record_last_oom(struct mem_cgroup *mem)
    > > }
    > >
    > > /*
    > > - * Currently used to update mapped file statistics, but the routine can be
    > > - * generalized to update other statistics as well.
    > > + * Generalized routine to update file cache's status for memcg.
    > > + *
    > > + * Before calling this, mapping->tree_lock should be held and preemption is
    > > + * disabled. Then, it's guarnteed that the page is not uncharged while we
    > > + * access page_cgroup. We can make use of that.
    > > */
    > IIUC, mapping->tree_lock is held with irq disabled, so I think "mapping->tree_lock
    > should be held with irq disabled" would be enouth.
    > And, as far as I can see, callers of this function have not ensured this yet in [4/4].
    >
    > how about:
    >
    > void mem_cgroup_update_stat_locked(...)
    > {
    > ...
    > }
    >
    > void mem_cgroup_update_stat_unlocked(mapping, ...)
    > {
    > spin_lock_irqsave(mapping->tree_lock, ...);
    > mem_cgroup_update_stat_locked();
    > spin_unlock_irqrestore(...);
    > }
    >
    Rather than tree_lock, lock_page_cgroup() can be used if tree_lock is not held.

    lock_page_cgroup();
    mem_cgroup_update_stat_locked();
    unlock_page_cgroup();

    Andrea-san, FILE_MAPPED is updated without treelock, at least. You can't depend
    on migration_lock about FILE_MAPPED.



    > > -void mem_cgroup_update_file_mapped(struct page *page, int val)
    > > +void mem_cgroup_update_stat(struct page *page,
    > > + enum mem_cgroup_stat_index idx, int val)
    > > {
    > I preffer "void mem_cgroup_update_page_stat(struct page *, enum mem_cgroup_page_stat_item, ..)"
    > as I said above.
    >
    > > struct mem_cgroup *mem;
    > > struct page_cgroup *pc;
    > >
    > > + if (mem_cgroup_disabled())
    > > + return;
    > > pc = lookup_page_cgroup(page);
    > > - if (unlikely(!pc))
    > > + if (unlikely(!pc) || !PageCgroupUsed(pc))
    > > return;
    > >
    > > - lock_page_cgroup(pc);
    > > - mem = pc->mem_cgroup;
    > > - if (!mem)
    > > - goto done;
    > > -
    > > - if (!PageCgroupUsed(pc))
    > > - goto done;
    > > -
    > > + lock_page_cgroup_migrate(pc);
    > > /*
    > > - * Preemption is already disabled. We can use __this_cpu_xxx
    > > - */
    > > - __this_cpu_add(mem->stat->count[MEM_CGROUP_STAT_FILE_MAPPED], val);
    > > -
    > > -done:
    > > - unlock_page_cgroup(pc);
    > > + * It's guarnteed that this page is never uncharged.
    > > + * The only racy problem is moving account among memcgs.
    > > + */
    > > + switch (idx) {
    > > + case MEM_CGROUP_STAT_FILE_MAPPED:
    > > + if (val > 0)
    > > + SetPageCgroupFileMapped(pc);
    > > + else
    > > + ClearPageCgroupFileMapped(pc);
    > > + break;
    > > + case MEM_CGROUP_STAT_FILE_DIRTY:
    > > + if (val > 0)
    > > + SetPageCgroupDirty(pc);
    > > + else
    > > + ClearPageCgroupDirty(pc);
    > > + break;
    > > + case MEM_CGROUP_STAT_WRITEBACK:
    > > + if (val > 0)
    > > + SetPageCgroupWriteback(pc);
    > > + else
    > > + ClearPageCgroupWriteback(pc);
    > > + break;
    > > + case MEM_CGROUP_STAT_WRITEBACK_TEMP:
    > > + if (val > 0)
    > > + SetPageCgroupWritebackTemp(pc);
    > > + else
    > > + ClearPageCgroupWritebackTemp(pc);
    > > + break;
    > > + case MEM_CGROUP_STAT_UNSTABLE_NFS:
    > > + if (val > 0)
    > > + SetPageCgroupUnstableNFS(pc);
    > > + else
    > > + ClearPageCgroupUnstableNFS(pc);
    > > + break;
    > > + default:
    > > + BUG();
    > > + break;
    > > + }
    > > + mem = pc->mem_cgroup;
    > > + if (likely(mem))
    > > + __this_cpu_add(mem->stat->count[idx], val);
    > > + unlock_page_cgroup_migrate(pc);
    > > }
    > > +EXPORT_SYMBOL_GPL(mem_cgroup_update_stat);
    > >
    > > /*
    > > * size of first charge trial. "32" comes from vmscan.c's magic value.
    > > @@ -1701,6 +1885,45 @@ static void __mem_cgroup_commit_charge(struct mem_cgroup *mem,
    > > memcg_check_events(mem, pc->page);
    > > }
    > >
    > > +/*
    > > + * Update file cache accounted statistics on task migration.
    > > + *
    > > + * TODO: We don't move charges of file (including shmem/tmpfs) pages for now.
    > > + * So, at the moment this function simply returns without updating accounted
    > > + * statistics, because we deal only with anonymous pages here.
    > > + */
    > This function is not unique to task migration. It's called from rmdir() too.
    > So this comment isn't needed.
    >
    > > +static void __mem_cgroup_update_file_stat(struct page_cgroup *pc,
    > > + struct mem_cgroup *from, struct mem_cgroup *to)
    > > +{
    > > + struct page *page = pc->page;
    > > +
    > > + if (!page_mapped(page) || PageAnon(page))
    > > + return;
    > > +
    > > + if (PageCgroupFileMapped(pc)) {
    > > + __this_cpu_dec(from->stat->count[MEM_CGROUP_STAT_FILE_MAPPED]);
    > > + __this_cpu_inc(to->stat->count[MEM_CGROUP_STAT_FILE_MAPPED]);
    > > + }
    > > + if (PageCgroupDirty(pc)) {
    > > + __this_cpu_dec(from->stat->count[MEM_CGROUP_STAT_FILE_DIRTY]);
    > > + __this_cpu_inc(to->stat->count[MEM_CGROUP_STAT_FILE_DIRTY]);
    > > + }
    > > + if (PageCgroupWriteback(pc)) {
    > > + __this_cpu_dec(from->stat->count[MEM_CGROUP_STAT_WRITEBACK]);
    > > + __this_cpu_inc(to->stat->count[MEM_CGROUP_STAT_WRITEBACK]);
    > > + }
    > > + if (PageCgroupWritebackTemp(pc)) {
    > > + __this_cpu_dec(
    > > + from->stat->count[MEM_CGROUP_STAT_WRITEBACK_TEMP]);
    > > + __this_cpu_inc(to->stat->count[MEM_CGROUP_STAT_WRITEBACK_TEMP]);
    > > + }
    > > + if (PageCgroupUnstableNFS(pc)) {
    > > + __this_cpu_dec(
    > > + from->stat->count[MEM_CGROUP_STAT_UNSTABLE_NFS]);
    > > + __this_cpu_inc(to->stat->count[MEM_CGROUP_STAT_UNSTABLE_NFS]);
    > > + }
    > > +}
    > > +
    > > /**
    > > * __mem_cgroup_move_account - move account of the page
    > > * @pc: page_cgroup of the page.
    > > @@ -1721,22 +1944,16 @@ static void __mem_cgroup_commit_charge(struct mem_cgroup *mem,
    > > static void __mem_cgroup_move_account(struct page_cgroup *pc,
    > > struct mem_cgroup *from, struct mem_cgroup *to, bool uncharge)
    > > {
    > > - struct page *page;
    > > -
    > > VM_BUG_ON(from == to);
    > > VM_BUG_ON(PageLRU(pc->page));
    > > VM_BUG_ON(!PageCgroupLocked(pc));
    > > VM_BUG_ON(!PageCgroupUsed(pc));
    > > VM_BUG_ON(pc->mem_cgroup != from);
    > >
    > > - page = pc->page;
    > > - if (page_mapped(page) && !PageAnon(page)) {
    > > - /* Update mapped_file data for mem_cgroup */
    > > - preempt_disable();
    > > - __this_cpu_dec(from->stat->count[MEM_CGROUP_STAT_FILE_MAPPED]);
    > > - __this_cpu_inc(to->stat->count[MEM_CGROUP_STAT_FILE_MAPPED]);
    > > - preempt_enable();
    > > - }
    > > + preempt_disable();
    > > + lock_page_cgroup_migrate(pc);
    > > + __mem_cgroup_update_file_stat(pc, from, to);
    > > +
    > > mem_cgroup_charge_statistics(from, pc, false);
    > > if (uncharge)
    > > /* This is not "cancel", but cancel_charge does all we need. */
    > > @@ -1745,6 +1962,8 @@ static void __mem_cgroup_move_account(struct page_cgroup *pc,
    > > /* caller should have done css_get */
    > > pc->mem_cgroup = to;
    > > mem_cgroup_charge_statistics(to, pc, true);
    > > + unlock_page_cgroup_migrate(pc);
    > > + preempt_enable();
    > Glad to see this cleanup :)
    > But, hmm, I don't think preempt_disable/enable() is enough(and bit_spin_lock/unlock()
    > does it anyway). lock/unlock_page_cgroup_migrate() can be called under irq context
    > (e.g. end_page_writeback()), so I think we must local_irq_disable()/enable() here.
    >
    Ah, hmm, yes. irq-disable is required.

    Thanks,
    -Kame

    >



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