Re: [PATCH 4/8] vmscan: Do not writeback filesystem pages in direct reclaim

KAMEZAWA Hiroyuki
2010-07-22T00:02:26Z

On Wed, 21 Jul 2010 15:27:10 +0100
Mel Gorman <mel@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