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Message-Id: <20200311171422.10484-4-david@redhat.com>
Date: Wed, 11 Mar 2020 18:14:15 +0100
From: David Hildenbrand <david@...hat.com>
To: linux-kernel@...r.kernel.org
Cc: linux-mm@...ck.org, virtio-dev@...ts.oasis-open.org,
virtualization@...ts.linux-foundation.org, kvm@...r.kernel.org,
Michal Hocko <mhocko@...nel.org>,
Andrew Morton <akpm@...ux-foundation.org>,
"Michael S . Tsirkin" <mst@...hat.com>,
David Hildenbrand <david@...hat.com>,
Jason Wang <jasowang@...hat.com>,
Oscar Salvador <osalvador@...e.de>,
Igor Mammedov <imammedo@...hat.com>,
Dave Young <dyoung@...hat.com>,
Dan Williams <dan.j.williams@...el.com>,
Pavel Tatashin <pasha.tatashin@...een.com>,
Stefan Hajnoczi <stefanha@...hat.com>,
Vlastimil Babka <vbabka@...e.cz>
Subject: [PATCH v2 03/10] virtio-mem: Paravirtualized memory hotunplug part 1
Unplugging subblocks of memory blocks that are offline is easy. All we
have to do is watch out for concurrent onlining activity.
Cc: "Michael S. Tsirkin" <mst@...hat.com>
Cc: Jason Wang <jasowang@...hat.com>
Cc: Oscar Salvador <osalvador@...e.de>
Cc: Michal Hocko <mhocko@...nel.org>
Cc: Igor Mammedov <imammedo@...hat.com>
Cc: Dave Young <dyoung@...hat.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>
Cc: Dan Williams <dan.j.williams@...el.com>
Cc: Pavel Tatashin <pasha.tatashin@...een.com>
Cc: Stefan Hajnoczi <stefanha@...hat.com>
Cc: Vlastimil Babka <vbabka@...e.cz>
Signed-off-by: David Hildenbrand <david@...hat.com>
---
drivers/virtio/virtio_mem.c | 116 +++++++++++++++++++++++++++++++++++-
1 file changed, 114 insertions(+), 2 deletions(-)
diff --git a/drivers/virtio/virtio_mem.c b/drivers/virtio/virtio_mem.c
index d8da656c9145..c1fc7f9c4acf 100644
--- a/drivers/virtio/virtio_mem.c
+++ b/drivers/virtio/virtio_mem.c
@@ -120,7 +120,7 @@ struct virtio_mem {
*
* When this lock is held the pointers can't change, ONLINE and
* OFFLINE blocks can't change the state and no subblocks will get
- * plugged.
+ * plugged/unplugged.
*/
struct mutex hotplug_mutex;
bool hotplug_active;
@@ -277,6 +277,12 @@ static int virtio_mem_mb_state_prepare_next_mb(struct virtio_mem *vm)
_mb_id++) \
if (virtio_mem_mb_get_state(_vm, _mb_id) == _state)
+#define virtio_mem_for_each_mb_state_rev(_vm, _mb_id, _state) \
+ for (_mb_id = _vm->next_mb_id - 1; \
+ _mb_id >= _vm->first_mb_id && _vm->nb_mb_state[_state]; \
+ _mb_id--) \
+ if (virtio_mem_mb_get_state(_vm, _mb_id) == _state)
+
/*
* Mark all selected subblocks plugged.
*
@@ -322,6 +328,19 @@ static bool virtio_mem_mb_test_sb_plugged(struct virtio_mem *vm,
bit + count;
}
+/*
+ * Test if all selected subblocks are unplugged.
+ */
+static bool virtio_mem_mb_test_sb_unplugged(struct virtio_mem *vm,
+ unsigned long mb_id, int sb_id,
+ int count)
+{
+ const int bit = (mb_id - vm->first_mb_id) * vm->nb_sb_per_mb + sb_id;
+
+ /* TODO: Helper similar to bitmap_set() */
+ return find_next_bit(vm->sb_bitmap, bit + count, bit) >= bit + count;
+}
+
/*
* Find the first plugged subblock. Returns vm->nb_sb_per_mb in case there is
* none.
@@ -511,6 +530,9 @@ static void virtio_mem_notify_offline(struct virtio_mem *vm,
BUG();
break;
}
+
+ /* trigger the workqueue, maybe we can now unplug memory. */
+ virtio_mem_retry(vm);
}
static void virtio_mem_notify_online(struct virtio_mem *vm, unsigned long mb_id,
@@ -1120,6 +1142,94 @@ static int virtio_mem_plug_request(struct virtio_mem *vm, uint64_t diff)
return rc;
}
+/*
+ * Unplug the desired number of plugged subblocks of an offline memory block.
+ * Will fail if any subblock cannot get unplugged (instead of skipping it).
+ *
+ * Will modify the state of the memory block. Might temporarily drop the
+ * hotplug_mutex.
+ *
+ * Note: Can fail after some subblocks were successfully unplugged.
+ */
+static int virtio_mem_mb_unplug_any_sb_offline(struct virtio_mem *vm,
+ unsigned long mb_id,
+ uint64_t *nb_sb)
+{
+ int rc;
+
+ rc = virtio_mem_mb_unplug_any_sb(vm, mb_id, nb_sb);
+
+ /* some subblocks might have been unplugged even on failure */
+ if (!virtio_mem_mb_test_sb_plugged(vm, mb_id, 0, vm->nb_sb_per_mb))
+ virtio_mem_mb_set_state(vm, mb_id,
+ VIRTIO_MEM_MB_STATE_OFFLINE_PARTIAL);
+ if (rc)
+ return rc;
+
+ if (virtio_mem_mb_test_sb_unplugged(vm, mb_id, 0, vm->nb_sb_per_mb)) {
+ /*
+ * Remove the block from Linux - this should never fail.
+ * Hinder the block from getting onlined by marking it
+ * unplugged. Temporarily drop the mutex, so
+ * any pending GOING_ONLINE requests can be serviced/rejected.
+ */
+ virtio_mem_mb_set_state(vm, mb_id,
+ VIRTIO_MEM_MB_STATE_UNUSED);
+
+ mutex_unlock(&vm->hotplug_mutex);
+ rc = virtio_mem_mb_remove(vm, mb_id);
+ BUG_ON(rc);
+ mutex_lock(&vm->hotplug_mutex);
+ }
+ return 0;
+}
+
+/*
+ * Try to unplug the requested amount of memory.
+ */
+static int virtio_mem_unplug_request(struct virtio_mem *vm, uint64_t diff)
+{
+ uint64_t nb_sb = diff / vm->subblock_size;
+ unsigned long mb_id;
+ int rc;
+
+ if (!nb_sb)
+ return 0;
+
+ /*
+ * We'll drop the mutex a couple of times when it is safe to do so.
+ * This might result in some blocks switching the state (online/offline)
+ * and we could miss them in this run - we will retry again later.
+ */
+ mutex_lock(&vm->hotplug_mutex);
+
+ /* Try to unplug subblocks of partially plugged offline blocks. */
+ virtio_mem_for_each_mb_state_rev(vm, mb_id,
+ VIRTIO_MEM_MB_STATE_OFFLINE_PARTIAL) {
+ rc = virtio_mem_mb_unplug_any_sb_offline(vm, mb_id,
+ &nb_sb);
+ if (rc || !nb_sb)
+ goto out_unlock;
+ cond_resched();
+ }
+
+ /* Try to unplug subblocks of plugged offline blocks. */
+ virtio_mem_for_each_mb_state_rev(vm, mb_id,
+ VIRTIO_MEM_MB_STATE_OFFLINE) {
+ rc = virtio_mem_mb_unplug_any_sb_offline(vm, mb_id,
+ &nb_sb);
+ if (rc || !nb_sb)
+ goto out_unlock;
+ cond_resched();
+ }
+
+ mutex_unlock(&vm->hotplug_mutex);
+ return 0;
+out_unlock:
+ mutex_unlock(&vm->hotplug_mutex);
+ return rc;
+}
+
/*
* Try to unplug all blocks that couldn't be unplugged before, for example,
* because the hypervisor was busy.
@@ -1202,8 +1312,10 @@ static void virtio_mem_run_wq(struct work_struct *work)
if (vm->requested_size > vm->plugged_size) {
diff = vm->requested_size - vm->plugged_size;
rc = virtio_mem_plug_request(vm, diff);
+ } else {
+ diff = vm->plugged_size - vm->requested_size;
+ rc = virtio_mem_unplug_request(vm, diff);
}
- /* TODO: try to unplug memory */
}
switch (rc) {
--
2.24.1
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