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

KAMEZAWA Hiroyuki
2010-07-22T09:26:59Z

On Thu, 22 Jul 2010 10:19:30 +0100
Mel Gorman <mel@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@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