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From: Johannes Weiner on 21 Jul 2010 10:50
On Wed, Jul 21, 2010 at 03:31:19PM +0100, Mel Gorman wrote:
> On Wed, Jul 21, 2010 at 04:28:44PM +0200, Johannes Weiner wrote:
> > On Wed, Jul 21, 2010 at 02:38:57PM +0100, Mel Gorman wrote:
> > > @@ -858,7 +872,7 @@ keep:
> > >
> > > free_page_list(&free_pages);
> > >
> > > - list_splice(&ret_pages, page_list);
> >
> > This will lose all retry pages forever, I think.
> >
>
> Above this is
>
> while (!list_empty(page_list)) {
> ...
> }
>
> page_list should be empty and keep_locked is putting the pages on ret_pages
> already so I think it's ok.

But ret_pages is function-local. Putting them back on the then-empty
page_list is to give them back to the caller, otherwise they are lost
in a dead stack slot.
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From: KAMEZAWA Hiroyuki on 21 Jul 2010 20:10
On Wed, 21 Jul 2010 15:27:10 +0100
Mel Gorman <mel(a)csn.ul.ie> wrote:

> On Wed, Jul 21, 2010 at 09:01:11PM +0900, KAMEZAWA Hiroyuki wrote:

> > But, hmm, memcg will have to select to enter this rounine based on
> > the result of 1st memory reclaim.
> >
>
> It has the option of igoring pages being dirtied but I worry that the
> container could be filled with dirty pages waiting for flushers to do
> something.

I'll prepare dirty_ratio for memcg. It's not easy but requested by I/O cgroup
guys, too...


>
> > >
> > > - /*
> > > - * The attempt at page out may have made some
> > > - * of the pages active, mark them inactive again.
> > > - */
> > > - nr_active = clear_active_flags(&page_list, NULL);
> > > - count_vm_events(PGDEACTIVATE, nr_active);
> > > + while (nr_reclaimed < nr_taken && nr_dirty && dirty_retry--) {
> > > + wakeup_flusher_threads(laptop_mode ? 0 : nr_dirty);
> > > + congestion_wait(BLK_RW_ASYNC, HZ/10);
> > >
> >
> > Congestion wait is required ?? Where the congestion happens ?
> > I'm sorry you already have some other trick in other patch.
> >
>
> It's to wait for the IO to occur.
>
1 tick penalty seems too large. I hope we can have some waitqueue in future.



> > > - nr_reclaimed += shrink_page_list(&page_list, sc, PAGEOUT_IO_SYNC);
> > > + /*
> > > + * The attempt at page out may have made some
> > > + * of the pages active, mark them inactive again.
> > > + */
> > > + nr_active = clear_active_flags(&page_list, NULL);
> > > + count_vm_events(PGDEACTIVATE, nr_active);
> > > +
> > > + nr_reclaimed += shrink_page_list(&page_list, sc,
> > > + PAGEOUT_IO_SYNC, &nr_dirty);
> > > + }
> >
> > Just a question. This PAGEOUT_IO_SYNC has some meanings ?
> >
>
> Yes, in pageout it will wait on pages currently being written back to be
> cleaned before trying to reclaim them.
>
Hmm. IIUC, this routine is called only when !current_is_kswapd() and
pageout is done only whne current_is_kswapd(). So, this seems ....
Wrong ?

Thanks,
-Kame




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From: KAMEZAWA Hiroyuki on 22 Jul 2010 05:30
On Thu, 22 Jul 2010 10:19:30 +0100
Mel Gorman <mel(a)csn.ul.ie> wrote:

> On Thu, Jul 22, 2010 at 08:57:34AM +0900, KAMEZAWA Hiroyuki wrote:
> > On Wed, 21 Jul 2010 15:27:10 +0100
> > Mel Gorman <mel(a)csn.ul.ie> wrote:

> > 1 tick penalty seems too large. I hope we can have some waitqueue in future.
> >
>
> congestion_wait() if congestion occurs goes onto a waitqueue that is
> woken if congestion clears. I didn't measure it this time around but I
> doubt it waits for HZ/10 much of the time.
>
Okay.

> > > > > - nr_reclaimed += shrink_page_list(&page_list, sc, PAGEOUT_IO_SYNC);
> > > > > + /*
> > > > > + * The attempt at page out may have made some
> > > > > + * of the pages active, mark them inactive again.
> > > > > + */
> > > > > + nr_active = clear_active_flags(&page_list, NULL);
> > > > > + count_vm_events(PGDEACTIVATE, nr_active);
> > > > > +
> > > > > + nr_reclaimed += shrink_page_list(&page_list, sc,
> > > > > + PAGEOUT_IO_SYNC, &nr_dirty);
> > > > > + }
> > > >
> > > > Just a question. This PAGEOUT_IO_SYNC has some meanings ?
> > > >
> > >
> > > Yes, in pageout it will wait on pages currently being written back to be
> > > cleaned before trying to reclaim them.
> > >
> > Hmm. IIUC, this routine is called only when !current_is_kswapd() and
> > pageout is done only whne current_is_kswapd(). So, this seems ....
> > Wrong ?
> >
>
> Both direct reclaim and kswapd can reach shrink_inactive_list
>
> Direct reclaim
> do_try_to_free_pages
> -> shrink_zones
> -> shrink_zone
> -> shrink_list
> -> shrink_inactive list <--- the routine in question
>
> Kswapd
> balance_pgdat
> -> shrink_zone
> -> shrink_list
> -> shrink_inactive_list
>
> pageout() is still called by direct reclaim if the page is anon so it
> will synchronously wait on those if PAGEOUT_IO_SYNC is set.

Ah, ok. I missed that. Thank you for kindly clarification.

Thanks,
-Kame

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