[RHEL7,COMMIT] ms/mm: workingset: eviction buckets for bigmem/lowbit machines

Submitted by Konstantin Khorenko on March 4, 2019, 2:52 p.m.


Message ID 201903041452.x24EqKH6002501@finist-ce7.sw.ru
State New
Series "Series without cover letter"
Headers show

Commit Message

Konstantin Khorenko March 4, 2019, 2:52 p.m.
The commit is pushed to "branch-rh7-3.10.0-957.5.1.vz7.84.x-ovz" and will appear at https://src.openvz.org/scm/ovz/vzkernel.git
after rh7-3.10.0-957.5.1.vz7.84.2
commit f079798583109f241048451e08f2ecdd28b0377e
Author: Johannes Weiner <hannes@cmpxchg.org>
Date:   Mon Mar 4 17:52:20 2019 +0300

    ms/mm: workingset: eviction buckets for bigmem/lowbit machines
    For per-cgroup thrash detection, we need to store the memcg ID inside
    the radix tree cookie as well.  However, on 32 bit that doesn't leave
    enough bits for the eviction timestamp to cover the necessary range of
    recently evicted pages.  The radix tree entry would look like this:
    12 bits means 4096 pages, means 16M worth of recently evicted pages.
    But refaults are actionable up to distances covering half of memory.  To
    not miss refaults, we have to stretch out the range at the cost of how
    precisely we can tell when a page was evicted.  This way we can shave
    off lower bits from the eviction timestamp until the necessary range is
    covered.  E.g.  grouping evictions into 1M buckets (256 pages) will
    stretch the longest representable refault distance to 4G.
    This patch implements eviction buckets that are automatically sized
    according to the available bits and the necessary refault range, in
    preparation for per-cgroup thrash detection.
    The maximum actionable distance is currently half of memory, but to
    support memory hotplug of up to 200% of boot-time memory, we size the
    buckets to cover double the distance.  Beyond that, thrashing won't be
    detectable anymore.
    During boot, the kernel will print out the exact parameters, like so:
      [    0.113929] workingset: timestamp_bits=12 max_order=18 bucket_order=6
    In this example, there are 12 radix entry bits available for the
    eviction timestamp, to cover a maximum distance of 2^18 pages (this is a
    1G machine).  Consequently, evictions must be grouped into buckets of
    2^6 pages, or 256K.
    Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
    Reviewed-by: Vladimir Davydov <vdavydov@virtuozzo.com>
    Cc: Michal Hocko <mhocko@suse.cz>
    Cc: David Rientjes <rientjes@google.com>
    Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
    Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
    (cherry picked from commit 612e44939c3c77245ac80843c0c7876c8cf97282)
    Signed-off-by: Andrey Ryabinin <aryabinin@virtuozzo.com>
 mm/workingset.c | 30 +++++++++++++++++++++++++++++-
 1 file changed, 29 insertions(+), 1 deletion(-)

Patch hide | download patch | download mbox

diff --git a/mm/workingset.c b/mm/workingset.c
index 22b66359d92d..45b98d9eaf78 100644
--- a/mm/workingset.c
+++ b/mm/workingset.c
@@ -156,8 +156,19 @@ 
+ * Eviction timestamps need to be able to cover the full range of
+ * actionable refaults. However, bits are tight in the radix tree
+ * entry, and after storing the identifier for the lruvec there might
+ * not be enough left to represent every single actionable refault. In
+ * that case, we have to sacrifice granularity for distance, and group
+ * evictions into coarser buckets by shaving off lower timestamp bits.
+ */
+static unsigned int bucket_order __read_mostly;
 static void *pack_shadow(unsigned long eviction, struct zone *zone)
+	eviction >>= bucket_order;
 	eviction = (eviction << NODES_SHIFT) | zone_to_nid(zone);
 	eviction = (eviction << ZONES_SHIFT) | zone_idx(zone);
 	eviction = (eviction << RADIX_TREE_EXCEPTIONAL_SHIFT);
@@ -178,7 +189,7 @@  static void unpack_shadow(void *shadow, struct zone **zonep,
 	entry >>= NODES_SHIFT;
 	*zonep = NODE_DATA(nid)->node_zones + zid;
-	*evictionp = entry;
+	*evictionp = entry << bucket_order;
@@ -412,8 +423,25 @@  static struct lock_class_key shadow_nodes_key;
 static int __init workingset_init(void)
+	unsigned int timestamp_bits;
+	unsigned int max_order;
 	int ret;
+	/*
+	 * Calculate the eviction bucket size to cover the longest
+	 * actionable refault distance, which is currently half of
+	 * memory (totalram_pages/2). However, memory hotplug may add
+	 * some more pages at runtime, so keep working with up to
+	 * double the initial memory by using totalram_pages as-is.
+	 */
+	timestamp_bits = BITS_PER_LONG - EVICTION_SHIFT;
+	max_order = fls_long(totalram_pages - 1);
+	if (max_order > timestamp_bits)
+		bucket_order = max_order - timestamp_bits;
+	printk("workingset: timestamp_bits=%d max_order=%d bucket_order=%u\n",
+	       timestamp_bits, max_order, bucket_order);
 	ret = list_lru_init_key(&workingset_shadow_nodes, &shadow_nodes_key);
 	if (ret)
 		goto err;