Messages in this thread | | | Date | Mon, 8 Mar 2010 10:56:41 +0900 | From | KAMEZAWA Hiroyuki <> | Subject | Re: [PATCH -mmotm 3/4] memcg: dirty pages accounting and limiting infrastructure |
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On Mon, 8 Mar 2010 10:44:47 +0900 Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp> wrote:
> > +/* > > + * mem_cgroup_update_page_stat_locked() - update memcg file cache's accounting > > + * @page: the page involved in a file cache operation. > > + * @idx: the particular file cache statistic. > > + * @charge: true to increment, false to decrement the statistic specified > > + * by @idx. > > + * > > + * Update memory cgroup file cache's accounting from a locked context. > > + * > > + * NOTE: must be called with mapping->tree_lock held. > > + */ > > +void mem_cgroup_update_page_stat_locked(struct page *page, > > + enum mem_cgroup_write_page_stat_item idx, bool charge) > > +{ > > + struct address_space *mapping = page_mapping(page); > > + struct page_cgroup *pc; > > + > > + if (mem_cgroup_disabled()) > > + return; > > + WARN_ON_ONCE(!irqs_disabled()); > > + WARN_ON_ONCE(mapping && !spin_is_locked(&mapping->tree_lock)); > > + > I think this is a wrong place to insert assertion. > The problem about page cgroup lock is that it can be interrupted in current implementation. > So, > > a) it must not be aquired under another lock which can be aquired in interrupt context, > such as mapping->tree_lock, to avoid: > > context1 context2 > lock_page_cgroup(pcA) > spin_lock_irq(&tree_lock) > lock_page_cgroup(pcA) <interrupted> > =>fail spin_lock_irqsave(&tree_lock) > =>fail > > b) it must not be aquired in interrupt context to avoid: > > lock_page_cgroup(pcA) > <interrupted> > lock_page_cgroup(pcA) > =>fail > > I think something like this would be better: > > @@ -83,8 +83,14 @@ static inline enum zone_type page_cgroup_zid(struct page_cgroup *pc) > return page_zonenum(pc->page); > } > > +#include <linux/irqflags.h> > +#include <linux/hardirq.h> > static inline void lock_page_cgroup(struct page_cgroup *pc) > { > +#ifdef CONFIG_DEBUG_VM > + WARN_ON_ONCE(irqs_disabled()); > + WARN_ON_ONCE(in_interrupt()); > +#endif > bit_spin_lock(PCG_LOCK, &pc->flags); > } > > > + pc = lookup_page_cgroup(page); > > + if (unlikely(!pc) || !PageCgroupUsed(pc)) > > + return; > > + mem_cgroup_update_page_stat(pc, idx, charge); > > +} > > +EXPORT_SYMBOL_GPL(mem_cgroup_update_page_stat_locked); > > + > > +/* > > + * mem_cgroup_update_page_stat_unlocked() - update memcg file cache's accounting > > + * @page: the page involved in a file cache operation. > > + * @idx: the particular file cache statistic. > > + * @charge: true to increment, false to decrement the statistic specified > > + * by @idx. > > + * > > + * Update memory cgroup file cache's accounting from an unlocked context. > > + */ > > +void mem_cgroup_update_page_stat_unlocked(struct page *page, > > + enum mem_cgroup_write_page_stat_item idx, bool charge) > > +{ > > + struct page_cgroup *pc; > > + > > + if (mem_cgroup_disabled()) > > + return; > > + pc = lookup_page_cgroup(page); > > + if (unlikely(!pc) || !PageCgroupUsed(pc)) > > + return; > > + lock_page_cgroup(pc); > > + mem_cgroup_update_page_stat(pc, idx, charge); > > unlock_page_cgroup(pc); > > } > > +EXPORT_SYMBOL_GPL(mem_cgroup_update_page_stat_unlocked); > > > IIUC, test_clear_page_writeback(at least) can be called under interrupt context. > This means lock_page_cgroup() is called under interrupt context, that is, > the case b) above can happen. > hmm... I don't have any good idea for now except disabling irq around page cgroup lock > to avoid all of these mess things. >
Hmm...simply IRQ-off for all updates ? But IIRC, clear_writeback is done under treelock.... No ?
Thanks, -Kame
> > Thanks, > Daisuke Nishimura. >
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