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

Mel Gorman
2010-07-21T14:27:29Z

On Wed, Jul 21, 2010 at 09:01:11PM +0900, KAMEZAWA Hiroyuki wrote:
> > <SNIP>
> >
> > /*
> > - * If we are direct reclaiming for contiguous pages and we do
> > + * If specific pages are needed such as with direct reclaiming
> > + * for contiguous pages or for memory containers and we do
> > * not reclaim everything in the list, try again and wait
> > - * for IO to complete. This will stall high-order allocations
> > - * but that should be acceptable to the caller
> > + * for IO to complete. This will stall callers that require
> > + * specific pages but it should be acceptable to the caller
> > */
> > - if (nr_reclaimed < nr_taken && !current_is_kswapd() &&
> > - sc->lumpy_reclaim_mode) {
> > - congestion_wait(BLK_RW_ASYNC, HZ/10);
> > + if (sc->may_writepage && !current_is_kswapd() &&
> > + (sc->lumpy_reclaim_mode || sc->mem_cgroup)) {
> > + int dirty_retry = MAX_SWAP_CLEAN_WAIT;
>
> Hmm, ok. I see what will happen to memcg.

Thanks

> 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.

> >
> > - /*
> > - * 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.

> > - 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.

--
Mel Gorman
Part-time Phd Student Linux Technology Center
University of Limerick IBM Dublin Software Lab