[Devel] Re: [PATCH -mmotm 3/4] memcg: dirty pages accounting and limiting infrastructure
KAMEZAWA Hiroyuki
kamezawa.hiroyu at jp.fujitsu.com
Thu Mar 4 17:58:55 PST 2010
On Fri, 5 Mar 2010 10:12:34 +0900
Daisuke Nishimura <nishimura at mxp.nes.nec.co.jp> wrote:
> On Thu, 4 Mar 2010 11:40:14 +0100, Andrea Righi <arighi at 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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