Messages in this thread | | | Date | Tue, 9 Jun 2009 09:47:46 +0100 | From | Mel Gorman <> | Subject | Re: [PATCH 2/3] Properly account for the number of page cache pages zone_reclaim() can reclaim |
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On Tue, Jun 09, 2009 at 05:19:41PM +0900, KOSAKI Motohiro wrote: > Hi > > > On NUMA machines, the administrator can configure zone_relcaim_mode that > > is a more targetted form of direct reclaim. On machines with large NUMA > > distances for example, a zone_reclaim_mode defaults to 1 meaning that clean > > unmapped pages will be reclaimed if the zone watermarks are not being met. > > > > There is a heuristic that determines if the scan is worthwhile but the > > problem is that the heuristic is not being properly applied and is basically > > assuming zone_reclaim_mode is 1 if it is enabled. > > > > This patch makes zone_reclaim() makes a better attempt at working out how > > many pages it might be able to reclaim given the current reclaim_mode. If it > > cannot clean pages, then NR_FILE_DIRTY number of pages are not candidates. If > > it cannot swap, then NR_FILE_MAPPED are not. This indirectly addresses tmpfs > > as those pages tend to be dirty as they are not cleaned by pdflush or sync. > > > > The ideal would be that the number of tmpfs pages would also be known > > and account for like NR_FILE_MAPPED as swap is required to discard them. > > A means of working this out quickly was not obvious but a comment is added > > noting the problem. > > > > Signed-off-by: Mel Gorman <mel@csn.ul.ie> > > --- > > mm/vmscan.c | 18 ++++++++++++++++-- > > 1 files changed, 16 insertions(+), 2 deletions(-) > > > > diff --git a/mm/vmscan.c b/mm/vmscan.c > > index ba211c1..ffe2f32 100644 > > --- a/mm/vmscan.c > > +++ b/mm/vmscan.c > > @@ -2380,6 +2380,21 @@ int zone_reclaim(struct zone *zone, gfp_t gfp_mask, unsigned int order) > > { > > int node_id; > > int ret; > > + int pagecache_reclaimable; > > + > > + /* > > + * Work out how many page cache pages we can reclaim in this mode. > > + * > > + * NOTE: Ideally, tmpfs pages would be accounted as if they were > > + * NR_FILE_MAPPED as swap is required to discard those > > + * pages even when they are clean. However, there is no > > + * way of quickly identifying the number of tmpfs pages > > + */ > > I think I and you tackle the same issue. > Please see vmscan-change-the-number-of-the-unmapped-files-in-zone-reclaim.patch in -mm. >
Awesome. This is why I posted the patches a bit earlier than I would normally. Stuff like this is found :D
> My intension mean, tmpfs page and swapcache increased NR_FILE_PAGES. > but they can't be reclaimed by zone_reclaim_mode==1. >
Sounds familiar!
> Then, I decide to use following calculation. > > + nr_unmapped_file_pages = zone_page_state(zone, NR_INACTIVE_FILE) + > + zone_page_state(zone, NR_ACTIVE_FILE) - > + zone_page_state(zone, NR_FILE_MAPPED); >
That should now be in a helper. If I use that calculation, it'll appear in three different places. I'll do the shuffling.
> > > + pagecache_reclaimable = zone_page_state(zone, NR_FILE_PAGES); > > + if (!(zone_reclaim_mode & RECLAIM_WRITE)) > > + pagecache_reclaimable -= zone_page_state(zone, NR_FILE_DIRTY); > > + if (!(zone_reclaim_mode & RECLAIM_SWAP)) > > + pagecache_reclaimable -= zone_page_state(zone, NR_FILE_MAPPED); > > if you hope to solve tmpfs issue, RECLAIM_WRITE/RECLAIM_SWAP are unrelated, I think.
For reclaim_zone() to do anything useful, the pages have to be cleaned and swapped and that needs RECLAIM_WRITE and RECLAIM_SWAP. So, how are they unrelated?
> Plus, Could you please see vmscan-zone_reclaim-use-may_swap.patch in -mm? > it improve RECLAIM_SWAP by another way. >
Looking now, I'm going to rebase this patchset on top of -mm where I can take advantage of that patch.
Thanks a lot
> > > > > > /* > > * Zone reclaim reclaims unmapped file backed pages and > > @@ -2391,8 +2406,7 @@ int zone_reclaim(struct zone *zone, gfp_t gfp_mask, unsigned int order) > > * if less than a specified percentage of the zone is used by > > * unmapped file backed pages. > > */ > > - if (zone_page_state(zone, NR_FILE_PAGES) - > > - zone_page_state(zone, NR_FILE_MAPPED) <= zone->min_unmapped_pages > > + if (pagecache_reclaimable <= zone->min_unmapped_pages > > && zone_page_state(zone, NR_SLAB_RECLAIMABLE) > > <= zone->min_slab_pages) > > return 0;
-- Mel Gorman Part-time Phd Student Linux Technology Center University of Limerick IBM Dublin Software Lab
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