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SubjectRe: [PATCH 1/3] Properly account for the number of page cache pages zone_reclaim() can reclaim
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> On NUMA machines, the administrator can configure zone_reclaim_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. The lack of proper detection can
> manfiest as high CPU usage as the LRU list is scanned uselessly.
>
> Historically, once enabled it was depending on NR_FILE_PAGES which may
> include swapcache pages that the reclaim_mode cannot deal with. Patch
> vmscan-change-the-number-of-the-unmapped-files-in-zone-reclaim.patch by
> Kosaki Motohiro noted that zone_page_state(zone, NR_FILE_PAGES) included
> pages that were not file-backed such as swapcache and made a calculation
> based on the inactive, active and mapped files. This is far superior
> when zone_reclaim==1 but if RECLAIM_SWAP is set, then NR_FILE_PAGES is a
> reasonable starting figure.
>
> This patch alters how zone_reclaim() works out how many pages it might be
> able to reclaim given the current reclaim_mode. If RECLAIM_SWAP is set
> in the reclaim_mode it will either consider NR_FILE_PAGES as potential
> candidates or else use NR_{IN}ACTIVE}_PAGES-NR_FILE_MAPPED to discount
> swapcache and other non-file-backed pages. If RECLAIM_WRITE is not set,
> then NR_FILE_DIRTY number of pages are not candidates. If RECLAIM_SWAP is
> not set, then NR_FILE_MAPPED are not.
>
> [mmotm note: This patch should be merged with or replace
> vmscan-change-the-number-of-the-unmapped-files-in-zone-reclaim. Kosaki?]
>
> [kosaki.motohiro@jp.fujitsu.com: Estimate unmapped pages minus tmpfs pages]
> [fengguang.wu@intel.com: Fix underflow problem in Kosaki's estimate]
> Signed-off-by: Mel Gorman <mel@csn.ul.ie>
> Reviewed-by: Rik van Riel <riel@redhat.com>
> Acked-by: Christoph Lameter <cl@linux-foundation.org>
> ---
> mm/vmscan.c | 55 +++++++++++++++++++++++++++++++++++++++++--------------
> 1 files changed, 41 insertions(+), 14 deletions(-)
>
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index 2ddcfc8..d832ba8 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -2333,6 +2333,44 @@ int sysctl_min_unmapped_ratio = 1;
> */
> int sysctl_min_slab_ratio = 5;
>
> +static inline unsigned long zone_unmapped_file_pages(struct zone *zone)
> +{
> + unsigned long file_mapped = zone_page_state(zone, NR_FILE_MAPPED);
> + unsigned long file_lru = zone_page_state(zone, NR_INACTIVE_FILE) +
> + zone_page_state(zone, NR_ACTIVE_FILE);
> +
> + /*
> + * It's possible for there to be more file mapped pages than
> + * accounted for by the pages on the file LRU lists because
> + * tmpfs pages accounted for as ANON can also be FILE_MAPPED
> + */
> + return (file_lru > file_mapped) ? (file_lru - file_mapped) : 0;
> +}
> +
> +/* Work out how many page cache pages we can reclaim in this reclaim_mode */
> +static long zone_pagecache_reclaimable(struct zone *zone)
> +{
> + long nr_pagecache_reclaimable;
> + long delta = 0;
> +
> + /*
> + * If RECLAIM_SWAP is set, then all file pages are considered
> + * potentially reclaimable. Otherwise, we have to worry about
> + * pages like swapcache and zone_unmapped_file_pages() provides
> + * a better estimate
> + */
> + if (zone_reclaim_mode & RECLAIM_SWAP)
> + nr_pagecache_reclaimable = zone_page_state(zone, NR_FILE_PAGES);
> + else
> + nr_pagecache_reclaimable = zone_unmapped_file_pages(zone);
> +
> + /* If we can't clean pages, remove dirty pages from consideration */
> + if (!(zone_reclaim_mode & RECLAIM_WRITE))
> + delta += zone_page_state(zone, NR_FILE_DIRTY);

no use delta?

> +
> + return nr_pagecache_reclaimable;
> +}
> +
> /*
> * Try to free up some pages from this zone through reclaim.
> */
> @@ -2355,7 +2393,6 @@ static int __zone_reclaim(struct zone *zone, gfp_t gfp_mask, unsigned int order)
> .isolate_pages = isolate_pages_global,
> };
> unsigned long slab_reclaimable;
> - long nr_unmapped_file_pages;
>
> disable_swap_token();
> cond_resched();
> @@ -2368,11 +2405,7 @@ static int __zone_reclaim(struct zone *zone, gfp_t gfp_mask, unsigned int order)
> reclaim_state.reclaimed_slab = 0;
> p->reclaim_state = &reclaim_state;
>
> - 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);
> -
> - if (nr_unmapped_file_pages > zone->min_unmapped_pages) {
> + if (zone_pagecache_reclaimable(zone) > zone->min_unmapped_pages) {

Documentation/sysctl/vm.txt says
=============================================================
min_unmapped_ratio:

This is available only on NUMA kernels.

A percentage of the total pages in each zone. Zone reclaim will only
occur if more than this percentage of pages are file backed and unmapped.
This is to insure that a minimal amount of local pages is still available for
file I/O even if the node is overallocated.

The default is 1 percent.

==============================================================
but your code condider more addional thing. Can you please change document too?


> /*
> * Free memory by calling shrink zone with increasing
> * priorities until we have enough memory freed.
> @@ -2419,8 +2452,6 @@ int zone_reclaim(struct zone *zone, gfp_t gfp_mask, unsigned int order)
> {
> int node_id;
> int ret;
> - long nr_unmapped_file_pages;
> - long nr_slab_reclaimable;
>
> /*
> * Zone reclaim reclaims unmapped file backed pages and
> @@ -2432,12 +2463,8 @@ 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.
> */
> - 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);
> - nr_slab_reclaimable = zone_page_state(zone, NR_SLAB_RECLAIMABLE);
> - if (nr_unmapped_file_pages <= zone->min_unmapped_pages &&
> - nr_slab_reclaimable <= zone->min_slab_pages)
> + if (zone_pagecache_reclaimable(zone) <= zone->min_unmapped_pages &&
> + zone_page_state(zone, NR_SLAB_RECLAIMABLE) <= zone->min_slab_pages)
> return 0;
>
> if (zone_is_all_unreclaimable(zone))
> --
> 1.5.6.5
>





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