lkml.org 
[lkml]   [2009]   [Jun]   [8]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH 2/3] Properly account for the number of page cache pages zone_reclaim() can reclaim
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


\
 
 \ /
  Last update: 2009-06-09 04:29    [W:0.173 / U:1.020 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site