On Tue, Nov 30, 2010 at 12:20:41PM +0100, Johannes Weiner wrote:
> On Tue, Nov 30, 2010 at 07:41:30AM +0900, Minchan Kim wrote:
>
> > diff --git a/mm/swap.c b/mm/swap.c
> > index 19e0812..1f1f435 100644
> > --- a/mm/swap.c
> > +++ b/mm/swap.c
> > @@ -275,28 +275,51 @@ void add_page_to_unevictable_list(struct page *page)
> > * into inative list's head. Because the VM expects the page would
> > * be writeout by flusher. The flusher's writeout is much effective
> > * than reclaimer's random writeout.
> > + *
> > + * If the page isn't page_mapped and dirty/writeback, the page
> > + * could reclaim asap using PG_reclaim.
> > + *
> > + * 1. active, mapped page -> none
> > + * 2. active, dirty/writeback page -> inactive, head, PG_reclaim
> > + * 3. inactive, mapped page -> none
> > + * 4. inactive, dirty/writeback page -> inactive, head, PG_reclaim
> > + * 5. Others -> none
> > + *
> > + * In 4, why it moves inactive's head, the VM expects the page would
> > + * be writeout by flusher. The flusher's writeout is much effective than
> > + * reclaimer's random writeout.
> > */
> > static void __lru_deactivate(struct page *page, struct zone *zone)
> > {
> > int lru, file;
> > - unsigned long vm_flags;
> > + int active = 0;
>
> vm_flags is never used in this series.
It's garbage in my old version which is used page_referenced.
>
> > - if (!PageLRU(page) || !PageActive(page))
> > + if (!PageLRU(page))
> > return;
> > -
> > /* Some processes are using the page */
> > if (page_mapped(page))
> > return;
> > -
> > - file = page_is_file_cache(page);
> > - lru = page_lru_base_type(page);
> > - del_page_from_lru_list(zone, page, lru + LRU_ACTIVE);
> > - ClearPageActive(page);
> > - ClearPageReferenced(page);
> > - add_page_to_lru_list(zone, page, lru);
> > - __count_vm_event(PGDEACTIVATE);
> > -
> > - update_page_reclaim_stat(zone, page, file, 0);
> > + if (PageActive(page))
> > + active = 1;
>
> active = PageActive(page)
Will fix.
>
> > + if (PageWriteback(page) || PageDirty(page)) {
> > + /*
> > + * PG_reclaim could be raced with end_page_writeback
> > + * It can make readahead confusing. But race window
> > + * is _really_ small and it's non-critical problem.
> > + */
> > + SetPageReclaim(page);
> > +
> > + file = page_is_file_cache(page);
> > + lru = page_lru_base_type(page);
> > + del_page_from_lru_list(zone, page, lru + active);
> > + ClearPageActive(page);
> > + ClearPageReferenced(page);
> > + add_page_to_lru_list(zone, page, lru);
> > + if (active)
> > + __count_vm_event(PGDEACTIVATE);
> > + update_page_reclaim_stat(zone, page, file, 0);
> > + }
>
> If we lose the race with writeback, the completion handler won't see
> PG_reclaim, won't move the page, and we have an unwanted clean cache
> page on the active list. Given the pagevec caching of those pages it
> could be rather likely that IO completes before the above executes.
>
> Shouldn't this be
>
> if (PageWriteback() || PageDirty()) {
> SetPageReclaim()
> move_to_inactive_head()
> } else {
> move_to_inactive_tail()
> }
>
> instead?
Fair enough.
Thanks, Hannes.
>
> Hannes
--
Kind regards,
Minchan Kim
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