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Message-Id: <20121219155901.c488bac2.akpm@linux-foundation.org>
Date: Wed, 19 Dec 2012 15:59:01 -0800
From: Andrew Morton <akpm@...ux-foundation.org>
To: Johannes Weiner <hannes@...xchg.org>
Cc: Rik van Riel <riel@...hat.com>, Michal Hocko <mhocko@...e.cz>,
Mel Gorman <mgorman@...e.de>, Hugh Dickins <hughd@...gle.com>,
Satoru Moriya <satoru.moriya@....com>, linux-mm@...ck.org,
linux-kernel@...r.kernel.org
Subject: Re: [patch 2/7] mm: vmscan: save work scanning (almost) empty LRU
lists
On Mon, 17 Dec 2012 13:12:32 -0500
Johannes Weiner <hannes@...xchg.org> wrote:
> In certain cases (kswapd reclaim, memcg target reclaim), a fixed
> minimum amount of pages is scanned from the LRU lists on each
> iteration, to make progress.
>
> Do not make this minimum bigger than the respective LRU list size,
> however, and save some busy work trying to isolate and reclaim pages
> that are not there.
>
> Empty LRU lists are quite common with memory cgroups in NUMA
> environments because there exists a set of LRU lists for each zone for
> each memory cgroup, while the memory of a single cgroup is expected to
> stay on just one node. The number of expected empty LRU lists is thus
>
> memcgs * (nodes - 1) * lru types
>
> Each attempt to reclaim from an empty LRU list does expensive size
> comparisons between lists, acquires the zone's lru lock etc. Avoid
> that.
>
> ...
>
> -#define SWAP_CLUSTER_MAX 32
> +#define SWAP_CLUSTER_MAX 32UL
You made me review the effects of this change. It looks OK. A few
cleanups are possible, please review.
I wonder what happens in __setup_per_zone_wmarks() if we set
SWAP_CLUSTER_MAX greater than 128.
From: Andrew Morton <akpm@...ux-foundation.org>
Subject: mm/page_alloc.c:__setup_per_zone_wmarks: make min_pages unsigned long
`int' is an inappropriate type for a number-of-pages counter.
While we're there, use the clamp() macro.
Cc: Johannes Weiner <hannes@...xchg.org>
Cc: Rik van Riel <riel@...hat.com>
Cc: Mel Gorman <mgorman@...e.de>
Cc: Michal Hocko <mhocko@...e.cz>
Cc: Hugh Dickins <hughd@...gle.com>
Cc: Satoru Moriya <satoru.moriya@....com>
Cc: Simon Jeons <simon.jeons@...il.com>
Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
---
mm/page_alloc.c | 7 ++-----
1 file changed, 2 insertions(+), 5 deletions(-)
diff -puN mm/page_alloc.c~a mm/page_alloc.c
--- a/mm/page_alloc.c~a
+++ a/mm/page_alloc.c
@@ -5258,13 +5258,10 @@ static void __setup_per_zone_wmarks(void
* deltas controls asynch page reclaim, and so should
* not be capped for highmem.
*/
- int min_pages;
+ unsigned long min_pages;
min_pages = zone->present_pages / 1024;
- if (min_pages < SWAP_CLUSTER_MAX)
- min_pages = SWAP_CLUSTER_MAX;
- if (min_pages > 128)
- min_pages = 128;
+ min_pages = clamp(min_pages, SWAP_CLUSTER_MAX, 128UL);
zone->watermark[WMARK_MIN] = min_pages;
} else {
/*
_
From: Andrew Morton <akpm@...ux-foundation.org>
Subject: mm/vmscan.c:shrink_lruvec(): switch to min()
"mm: vmscan: save work scanning (almost) empty LRU lists" made
SWAP_CLUSTER_MAX an unsigned long.
Cc: Johannes Weiner <hannes@...xchg.org>
Cc: Rik van Riel <riel@...hat.com>
Cc: Mel Gorman <mgorman@...e.de>
Cc: Michal Hocko <mhocko@...e.cz>
Cc: Hugh Dickins <hughd@...gle.com>
Cc: Satoru Moriya <satoru.moriya@....com>
Cc: Simon Jeons <simon.jeons@...il.com>
Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
---
mm/vmscan.c | 3 +--
1 file changed, 1 insertion(+), 2 deletions(-)
diff -puN mm/vmscan.c~a mm/vmscan.c
--- a/mm/vmscan.c~a
+++ a/mm/vmscan.c
@@ -1873,8 +1873,7 @@ restart:
nr[LRU_INACTIVE_FILE]) {
for_each_evictable_lru(lru) {
if (nr[lru]) {
- nr_to_scan = min_t(unsigned long,
- nr[lru], SWAP_CLUSTER_MAX);
+ nr_to_scan = min(nr[lru], SWAP_CLUSTER_MAX);
nr[lru] -= nr_to_scan;
nr_reclaimed += shrink_list(lru, nr_to_scan,
_
From: Andrew Morton <akpm@...ux-foundation.org>
Subject: mm/vmscan.c:__zone_reclaim(): replace max_t() with max()
"mm: vmscan: save work scanning (almost) empty LRU lists" made
SWAP_CLUSTER_MAX an unsigned long.
Cc: Johannes Weiner <hannes@...xchg.org>
Cc: Rik van Riel <riel@...hat.com>
Cc: Mel Gorman <mgorman@...e.de>
Cc: Michal Hocko <mhocko@...e.cz>
Cc: Hugh Dickins <hughd@...gle.com>
Cc: Satoru Moriya <satoru.moriya@....com>
Cc: Simon Jeons <simon.jeons@...il.com>
Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
---
mm/vmscan.c | 3 +--
1 file changed, 1 insertion(+), 2 deletions(-)
diff -puN mm/vmscan.c~mm-vmscanc-__zone_reclaim-replace-max_t-with-max mm/vmscan.c
--- a/mm/vmscan.c~mm-vmscanc-__zone_reclaim-replace-max_t-with-max
+++ a/mm/vmscan.c
@@ -3347,8 +3347,7 @@ static int __zone_reclaim(struct zone *z
.may_writepage = !!(zone_reclaim_mode & RECLAIM_WRITE),
.may_unmap = !!(zone_reclaim_mode & RECLAIM_SWAP),
.may_swap = 1,
- .nr_to_reclaim = max_t(unsigned long, nr_pages,
- SWAP_CLUSTER_MAX),
+ .nr_to_reclaim = max(nr_pages, SWAP_CLUSTER_MAX),
.gfp_mask = gfp_mask,
.order = order,
.priority = ZONE_RECLAIM_PRIORITY,
_
--
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