On Wed, Dec 19, 2012 at 03:59:01PM -0800, Andrew Morton wrote:

On Mon, 17 Dec 2012 13:12:32 -0500
Johannes Weiner [off-list ref] wrote:

quoted

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.

In the current clamp() implementation max overrides min, so...

BUILD_BUG_ON()?  Probably unnecessary, it seems like a rather
arbitrary range to begin with.

From: Andrew Morton <akpm@linux-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@cmpxchg.org>
Cc: Rik van Riel <redacted>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Michal Hocko <redacted>
Cc: Hugh Dickins <hughd@google.com>
Cc: Satoru Moriya <redacted>
Cc: Simon Jeons <redacted>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

Acked-by: Johannes Weiner <hannes@cmpxchg.org>

From: Andrew Morton <akpm@linux-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@cmpxchg.org>
Cc: Rik van Riel <redacted>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Michal Hocko <redacted>
Cc: Hugh Dickins <hughd@google.com>
Cc: Satoru Moriya <redacted>
Cc: Simon Jeons <redacted>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

Acked-by: Johannes Weiner <hannes@cmpxchg.org>

From: Andrew Morton <akpm@linux-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@cmpxchg.org>
Cc: Rik van Riel <redacted>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Michal Hocko <redacted>
Cc: Hugh Dickins <hughd@google.com>
Cc: Satoru Moriya <redacted>
Cc: Simon Jeons <redacted>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

Acked-by: Johannes Weiner <hannes@cmpxchg.org>

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