Messages in this thread | | | Date | Tue, 9 Jun 2009 10:25:49 +0800 | From | Wu Fengguang <> | Subject | Re: [PATCH 2/3] Properly account for the number of page cache pages zone_reclaim() can reclaim |
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On Mon, Jun 08, 2009 at 09:01:29PM +0800, Mel Gorman wrote: > 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.
No, tmpfs pages are not accounted in NR_FILE_DIRTY because of the BDI_CAP_NO_ACCT_AND_WRITEBACK bits.
> 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.
I'd rather prefer it be accounted separately than to muck up NR_FILE_MAPPED :)
> + 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 > + */
So can you remove the note on NR_FILE_MAPPED?
> + 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);
So the "if" can be removed because NR_FILE_MAPPED is not related to swapping?
Thanks, Fengguang
> /* > * 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; > -- > 1.5.6.5
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