Re: [PATCH 2/2] memcg: dirty pages instrumentation

[Andrea Righi]

On Mon, Feb 22, 2010 at 07:20:09PM +0100, Peter Zijlstra wrote:
> On Sun, 2010-02-21 at 16:18 +0100, Andrea Righi wrote:
> > @@ -137,10 +137,11 @@ static struct prop_descriptor vm_dirties;
> >   */
> >  static int calc_period_shift(void)
> >  {
> > -       unsigned long dirty_total;
> > +       unsigned long dirty_total, dirty_bytes;
> >  
> > -       if (vm_dirty_bytes)
> > -               dirty_total = vm_dirty_bytes / PAGE_SIZE;
> > +       dirty_bytes = mem_cgroup_dirty_bytes();
> > +       if (dirty_bytes)
> > +               dirty_total = dirty_bytes / PAGE_SIZE;
> >         else
> >                 dirty_total = (vm_dirty_ratio * determine_dirtyable_memory()) /
> >                                 100;
> > @@ -406,14 +407,20 @@ static unsigned long highmem_dirtyable_memory(unsigned long total)
> >   */
> >  unsigned long determine_dirtyable_memory(void)
> >  {
> > -       unsigned long x;
> > -
> > -       x = global_page_state(NR_FREE_PAGES) + global_reclaimable_pages();
> > -
> > +       unsigned long memcg_memory, memory;
> > +
> > +       memory = global_page_state(NR_FREE_PAGES) + global_reclaimable_pages();
> > +       memcg_memory = mem_cgroup_page_state(MEMCG_NR_FREE_PAGES);
> > +       if (memcg_memory > 0) {
> > +               memcg_memory +=
> > +                       mem_cgroup_page_state(MEMCG_NR_RECLAIMABLE_PAGES);
> > +               if (memcg_memory < memory)
> > +                       return memcg_memory;
> > +       }
> >         if (!vm_highmem_is_dirtyable)
> > -               x -= highmem_dirtyable_memory(x);
> > +               memory -= highmem_dirtyable_memory(memory);
> >  
> > -       return x + 1;   /* Ensure that we never return 0 */
> > +       return memory + 1;      /* Ensure that we never return 0 */
> >  }
> >  
> >  void
> > @@ -421,12 +428,13 @@ get_dirty_limits(unsigned long *pbackground, unsigned long *pdirty,
> >                  unsigned long *pbdi_dirty, struct backing_dev_info *bdi)
> >  {
> >         unsigned long background;
> > -       unsigned long dirty;
> > +       unsigned long dirty, dirty_bytes;
> >         unsigned long available_memory = determine_dirtyable_memory();
> >         struct task_struct *tsk;
> >  
> > -       if (vm_dirty_bytes)
> > -               dirty = DIV_ROUND_UP(vm_dirty_bytes, PAGE_SIZE);
> > +       dirty_bytes = mem_cgroup_dirty_bytes();
> > +       if (dirty_bytes)
> > +               dirty = DIV_ROUND_UP(dirty_bytes, PAGE_SIZE);
> >         else {
> >                 int dirty_ratio;
> >  
> > @@ -505,9 +513,17 @@ static void balance_dirty_pages(struct address_space *mapping,
> >                 get_dirty_limits(&background_thresh, &dirty_thresh,
> >                                 &bdi_thresh, bdi);
> >  
> > -               nr_reclaimable = global_page_state(NR_FILE_DIRTY) +
> > +               nr_reclaimable = mem_cgroup_page_state(MEMCG_NR_FILE_DIRTY);
> > +               if (nr_reclaimable == 0) {
> > +                       nr_reclaimable = global_page_state(NR_FILE_DIRTY) +
> >                                         global_page_state(NR_UNSTABLE_NFS);
> > -               nr_writeback = global_page_state(NR_WRITEBACK);
> > +                       nr_writeback = global_page_state(NR_WRITEBACK);
> > +               } else {
> > +                       nr_reclaimable +=
> > +                               mem_cgroup_page_state(MEMCG_NR_UNSTABLE_NFS);
> > +                       nr_writeback =
> > +                               mem_cgroup_page_state(MEMCG_NR_WRITEBACK);
> > +               }
> >  
> >                 bdi_nr_reclaimable = bdi_stat(bdi, BDI_RECLAIMABLE);
> >                 bdi_nr_writeback = bdi_stat(bdi, BDI_WRITEBACK);
> > @@ -660,6 +676,8 @@ void throttle_vm_writeout(gfp_t gfp_mask)
> >         unsigned long dirty_thresh;
> >  
> >          for ( ; ; ) {
> > +               unsigned long dirty;
> > +
> >                 get_dirty_limits(&background_thresh, &dirty_thresh, NULL, NULL);
> >  
> >                  /*
> > @@ -668,10 +686,15 @@ void throttle_vm_writeout(gfp_t gfp_mask)
> >                   */
> >                  dirty_thresh += dirty_thresh / 10;      /* wheeee... */
> >  
> > -                if (global_page_state(NR_UNSTABLE_NFS) +
> > -                       global_page_state(NR_WRITEBACK) <= dirty_thresh)
> > -                               break;
> > -                congestion_wait(BLK_RW_ASYNC, HZ/10);
> > +               dirty = mem_cgroup_page_state(MEMCG_NR_WRITEBACK);
> > +               if (dirty < 0)
> > +                       dirty = global_page_state(NR_UNSTABLE_NFS) +
> > +                               global_page_state(NR_WRITEBACK);
> > +               else
> > +                       dirty += mem_cgroup_page_state(MEMCG_NR_UNSTABLE_NFS);
> > +               if (dirty <= dirty_thresh)
> > +                       break;
> > +               congestion_wait(BLK_RW_ASYNC, HZ/10);
> >  
> >                 /*
> >                  * The caller might hold locks which can prevent IO completion 
> 
> 
> This stuff looks really rather horrible, 
> 
> Relying on these cgroup functions returning 0 seems fragile, some of
> them can really be 0. Also sprinkling all that if cgroup foo all over
> the place leads to these ugly indentation problems you have.
> 
> How about pulling all these things into separate functions, and using a
> proper mem_cgroup_has_dirty() function to select on?

Agreed. Will do in the next version of the patch.

Thanks,
-Andrea
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