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Date: Thu, 11 Jun 2009 09:48:53 -0400 (EDT)
From: Christoph Lameter <cl@...ux-foundation.org>
To: Mel Gorman <mel@....ul.ie>
cc: Andrew Morton <akpm@...ux-foundation.org>,
KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
Rik van Riel <riel@...hat.com>,
Wu Fengguang <fengguang.wu@...el.com>, linuxram@...ibm.com,
linux-mm <linux-mm@...ck.org>,
LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/3] Do not unconditionally treat zones that fail
zone_reclaim() as full
It needs to be mentioned that this fixes a bug introduced in 2.6.19.
Possibly a portion of this code needs to be backported to stable.
On Thu, 11 Jun 2009, Mel Gorman wrote:
> 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. The problem is that zone_reclaim() failing at all means the zone
> gets marked full.
>
> This can cause situations where a zone is usable, but is being skipped
> because it has been considered full. Take a situation where a large tmpfs
> mount is occuping a large percentage of memory overall. The pages do not
> get cleaned or reclaimed by zone_reclaim(), but the zone gets marked full
> and the zonelist cache considers them not worth trying in the future.
>
> This patch makes zone_reclaim() return more fine-grained information about
> what occured when zone_reclaim() failued. The zone only gets marked full if
> it really is unreclaimable. If it's a case that the scan did not occur or
> if enough pages were not reclaimed with the limited reclaim_mode, then the
> zone is simply skipped.
>
> There is a side-effect to this patch. Currently, if zone_reclaim()
> successfully reclaimed SWAP_CLUSTER_MAX, an allocation attempt would
> go ahead. With this patch applied, zone watermarks are rechecked after
> zone_reclaim() does some work.
>
> Signed-off-by: Mel Gorman <mel@....ul.ie>
> Reviewed-by: Wu Fengguang <fengguang.wu@...el.com>
> Reviewed-by: Rik van Riel <riel@...hat.com>
> Reviewed-by: KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
> ---
> mm/internal.h | 4 ++++
> mm/page_alloc.c | 26 ++++++++++++++++++++++----
> mm/vmscan.c | 11 ++++++-----
> 3 files changed, 32 insertions(+), 9 deletions(-)
>
> diff --git a/mm/internal.h b/mm/internal.h
> index f02c750..f290c4d 100644
> --- a/mm/internal.h
> +++ b/mm/internal.h
> @@ -259,4 +259,8 @@ int __get_user_pages(struct task_struct *tsk, struct mm_struct *mm,
> unsigned long start, int len, int flags,
> struct page **pages, struct vm_area_struct **vmas);
>
> +#define ZONE_RECLAIM_NOSCAN -2
> +#define ZONE_RECLAIM_FULL -1
> +#define ZONE_RECLAIM_SOME 0
> +#define ZONE_RECLAIM_SUCCESS 1
> #endif
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index d35e753..667ffbb 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -1477,15 +1477,33 @@ zonelist_scan:
> BUILD_BUG_ON(ALLOC_NO_WATERMARKS < NR_WMARK);
> if (!(alloc_flags & ALLOC_NO_WATERMARKS)) {
> unsigned long mark;
> + int ret;
> +
> mark = zone->watermark[alloc_flags & ALLOC_WMARK_MASK];
> - if (!zone_watermark_ok(zone, order, mark,
> - classzone_idx, alloc_flags)) {
> - if (!zone_reclaim_mode ||
> - !zone_reclaim(zone, gfp_mask, order))
> + if (zone_watermark_ok(zone, order, mark,
> + classzone_idx, alloc_flags))
> + goto try_this_zone;
> +
> + if (zone_reclaim_mode == 0)
> + goto this_zone_full;
> +
> + ret = zone_reclaim(zone, gfp_mask, order);
> + switch (ret) {
> + case ZONE_RECLAIM_NOSCAN:
> + /* did not scan */
> + goto try_next_zone;
> + case ZONE_RECLAIM_FULL:
> + /* scanned but unreclaimable */
> + goto this_zone_full;
> + default:
> + /* did we reclaim enough */
> + if (!zone_watermark_ok(zone, order, mark,
> + classzone_idx, alloc_flags))
> goto this_zone_full;
> }
> }
>
> +try_this_zone:
> page = buffered_rmqueue(preferred_zone, zone, order,
> gfp_mask, migratetype);
> if (page)
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index d832ba8..7b8eb3f 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -2465,16 +2465,16 @@ int zone_reclaim(struct zone *zone, gfp_t gfp_mask, unsigned int order)
> */
> if (zone_pagecache_reclaimable(zone) <= zone->min_unmapped_pages &&
> zone_page_state(zone, NR_SLAB_RECLAIMABLE) <= zone->min_slab_pages)
> - return 0;
> + return ZONE_RECLAIM_FULL;
>
> if (zone_is_all_unreclaimable(zone))
> - return 0;
> + return ZONE_RECLAIM_FULL;
>
> /*
> * Do not scan if the allocation should not be delayed.
> */
> if (!(gfp_mask & __GFP_WAIT) || (current->flags & PF_MEMALLOC))
> - return 0;
> + return ZONE_RECLAIM_NOSCAN;
>
> /*
> * Only run zone reclaim on the local zone or on zones that do not
> @@ -2484,10 +2484,11 @@ int zone_reclaim(struct zone *zone, gfp_t gfp_mask, unsigned int order)
> */
> node_id = zone_to_nid(zone);
> if (node_state(node_id, N_CPU) && node_id != numa_node_id())
> - return 0;
> + return ZONE_RECLAIM_NOSCAN;
>
> if (zone_test_and_set_flag(zone, ZONE_RECLAIM_LOCKED))
> - return 0;
> + return ZONE_RECLAIM_NOSCAN;
> +
> ret = __zone_reclaim(zone, gfp_mask, order);
> zone_clear_flag(zone, ZONE_RECLAIM_LOCKED);
>
>
--
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