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Subject[PATCH RFC v4 13/13] virtio-mem: Drop slab objects when unplug continues to fail
Date
Start dropping slab objects after 30 minutes and repeat every 30 minutes
in case we can't unplug more memory using alloc_contig_range().
Log messages and make it configurable. Enable dropping slab objects as
default (especially, reclaimable slab objects that are not movable).

In the future, we might want to implement+use drop_slab_range(), which
will also come in handy for other users (e.g., offlining, gigantic huge
pages).

Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: "Michael S. Tsirkin" <mst@redhat.com>
Cc: Jason Wang <jasowang@redhat.com>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: Igor Mammedov <imammedo@redhat.com>
Cc: Dave Young <dyoung@redhat.com>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: Pavel Tatashin <pasha.tatashin@soleen.com>
Cc: Stefan Hajnoczi <stefanha@redhat.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: linux-fsdevel@vger.kernel.org
Signed-off-by: David Hildenbrand <david@redhat.com>
---
drivers/virtio/virtio_mem.c | 30 ++++++++++++++++++++++++++++++
1 file changed, 30 insertions(+)

diff --git a/drivers/virtio/virtio_mem.c b/drivers/virtio/virtio_mem.c
index 3a57434f92ed..8f25f7453a08 100644
--- a/drivers/virtio/virtio_mem.c
+++ b/drivers/virtio/virtio_mem.c
@@ -25,6 +25,11 @@ static bool unplug_online = true;
module_param(unplug_online, bool, 0644);
MODULE_PARM_DESC(unplug_online, "Try to unplug online memory");

+static bool drop_slab_objects = true;
+module_param(drop_slab_objects, bool, 0644);
+MODULE_PARM_DESC(drop_slab_objects,
+ "Drop slab objects when unplug continues to fail");
+
enum virtio_mem_mb_state {
/* Unplugged, not added to Linux. Can be reused later. */
VIRTIO_MEM_MB_STATE_UNUSED = 0,
@@ -1384,6 +1389,7 @@ static int virtio_mem_mb_unplug_any_sb_online(struct virtio_mem *vm,
static int virtio_mem_unplug_request(struct virtio_mem *vm, uint64_t diff)
{
uint64_t nb_sb = diff / vm->subblock_size;
+ bool retried = false;
unsigned long mb_id;
int rc;

@@ -1421,6 +1427,7 @@ static int virtio_mem_unplug_request(struct virtio_mem *vm, uint64_t diff)
return 0;
}

+retry_locked:
/* Try to unplug subblocks of partially plugged online blocks. */
virtio_mem_for_each_mb_state(vm, mb_id,
VIRTIO_MEM_MB_STATE_ONLINE_PARTIAL) {
@@ -1445,6 +1452,29 @@ static int virtio_mem_unplug_request(struct virtio_mem *vm, uint64_t diff)
}

mutex_unlock(&vm->hotplug_mutex);
+
+ /*
+ * If we can't unplug the requested amount of memory for a long time,
+ * start freeing up memory in caches. This might harm performance,
+ * is configurable, and we log a message. Retry imemdiately a second
+ * time - then wait another VIRTIO_MEM_RETRY_TIMER_MAX_MS.
+ */
+ if (nb_sb && !retried && drop_slab_objects &&
+ vm->retry_timer_ms == VIRTIO_MEM_RETRY_TIMER_MAX_MS) {
+ if (vm->nid == NUMA_NO_NODE) {
+ dev_info(&vm->vdev->dev, "dropping all slab objects\n");
+ drop_slab();
+ } else {
+ dev_info(&vm->vdev->dev,
+ "dropping all slab objects on node=%d\n",
+ vm->nid);
+ drop_slab_node(vm->nid);
+ }
+ retried = true;
+ mutex_lock(&vm->hotplug_mutex);
+ goto retry_locked;
+ }
+
return nb_sb ? -EBUSY : 0;
out_unlock:
mutex_unlock(&vm->hotplug_mutex);
--
2.23.0
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