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Message-ID: <20201019075406.GE54484@L-31X9LVDL-1304.local>
Date: Mon, 19 Oct 2020 15:54:06 +0800
From: Wei Yang <richard.weiyang@...ux.alibaba.com>
To: David Hildenbrand <david@...hat.com>
Cc: linux-kernel@...r.kernel.org, linux-mm@...ck.org,
virtualization@...ts.linux-foundation.org,
Andrew Morton <akpm@...ux-foundation.org>,
"Michael S . Tsirkin" <mst@...hat.com>,
Jason Wang <jasowang@...hat.com>,
Pankaj Gupta <pankaj.gupta.linux@...il.com>,
Michal Hocko <mhocko@...nel.org>,
Oscar Salvador <osalvador@...e.de>,
Wei Yang <richard.weiyang@...ux.alibaba.com>
Subject: Re: [PATCH v1 29/29] virtio-mem: Big Block Mode (BBM) - safe memory
hotunplug
On Mon, Oct 12, 2020 at 02:53:23PM +0200, David Hildenbrand wrote:
>Let's add a safe mechanism to unplug memory, avoiding long/endless loops
>when trying to offline memory - similar to in SBM.
>
>Fake-offline all memory (via alloc_contig_range()) before trying to
>offline+remove it. Use this mode as default, but allow to enable the other
>mode explicitly (which could give better memory hotunplug guarantees in
I don't get the point how unsafe mode would have a better guarantees?
>some environments).
>
>The "unsafe" mode can be enabled e.g., via virtio_mem.bbm_safe_unplug=0
>on the cmdline.
>
>Cc: "Michael S. Tsirkin" <mst@...hat.com>
>Cc: Jason Wang <jasowang@...hat.com>
>Cc: Pankaj Gupta <pankaj.gupta.linux@...il.com>
>Cc: Michal Hocko <mhocko@...nel.org>
>Cc: Oscar Salvador <osalvador@...e.de>
>Cc: Wei Yang <richard.weiyang@...ux.alibaba.com>
>Cc: Andrew Morton <akpm@...ux-foundation.org>
>Signed-off-by: David Hildenbrand <david@...hat.com>
>---
> drivers/virtio/virtio_mem.c | 97 ++++++++++++++++++++++++++++++++++++-
> 1 file changed, 95 insertions(+), 2 deletions(-)
>
>diff --git a/drivers/virtio/virtio_mem.c b/drivers/virtio/virtio_mem.c
>index 6bcd0acbff32..09f11489be6f 100644
>--- a/drivers/virtio/virtio_mem.c
>+++ b/drivers/virtio/virtio_mem.c
>@@ -37,6 +37,11 @@ module_param(bbm_block_size, ulong, 0444);
> MODULE_PARM_DESC(bbm_block_size,
> "Big Block size in bytes. Default is 0 (auto-detection).");
>
>+static bool bbm_safe_unplug = true;
>+module_param(bbm_safe_unplug, bool, 0444);
>+MODULE_PARM_DESC(bbm_safe_unplug,
>+ "Use a safe unplug mechanism in BBM, avoiding long/endless loops");
>+
> /*
> * virtio-mem currently supports the following modes of operation:
> *
>@@ -87,6 +92,8 @@ enum virtio_mem_bbm_bb_state {
> VIRTIO_MEM_BBM_BB_PLUGGED,
> /* Plugged and added to Linux. */
> VIRTIO_MEM_BBM_BB_ADDED,
>+ /* All online parts are fake-offline, ready to remove. */
>+ VIRTIO_MEM_BBM_BB_FAKE_OFFLINE,
> VIRTIO_MEM_BBM_BB_COUNT
> };
>
>@@ -889,6 +896,32 @@ static void virtio_mem_sbm_notify_cancel_offline(struct virtio_mem *vm,
> }
> }
>
>+static void virtio_mem_bbm_notify_going_offline(struct virtio_mem *vm,
>+ unsigned long bb_id,
>+ unsigned long pfn,
>+ unsigned long nr_pages)
>+{
>+ /*
>+ * When marked as "fake-offline", all online memory of this device block
>+ * is allocated by us. Otherwise, we don't have any memory allocated.
>+ */
>+ if (virtio_mem_bbm_get_bb_state(vm, bb_id) !=
>+ VIRTIO_MEM_BBM_BB_FAKE_OFFLINE)
>+ return;
>+ virtio_mem_fake_offline_going_offline(pfn, nr_pages);
>+}
>+
>+static void virtio_mem_bbm_notify_cancel_offline(struct virtio_mem *vm,
>+ unsigned long bb_id,
>+ unsigned long pfn,
>+ unsigned long nr_pages)
>+{
>+ if (virtio_mem_bbm_get_bb_state(vm, bb_id) !=
>+ VIRTIO_MEM_BBM_BB_FAKE_OFFLINE)
>+ return;
>+ virtio_mem_fake_offline_cancel_offline(pfn, nr_pages);
>+}
>+
> /*
> * This callback will either be called synchronously from add_memory() or
> * asynchronously (e.g., triggered via user space). We have to be careful
>@@ -949,6 +982,10 @@ static int virtio_mem_memory_notifier_cb(struct notifier_block *nb,
> vm->hotplug_active = true;
> if (vm->in_sbm)
> virtio_mem_sbm_notify_going_offline(vm, id);
>+ else
>+ virtio_mem_bbm_notify_going_offline(vm, id,
>+ mhp->start_pfn,
>+ mhp->nr_pages);
> break;
> case MEM_GOING_ONLINE:
> mutex_lock(&vm->hotplug_mutex);
>@@ -999,6 +1036,10 @@ static int virtio_mem_memory_notifier_cb(struct notifier_block *nb,
> break;
> if (vm->in_sbm)
> virtio_mem_sbm_notify_cancel_offline(vm, id);
>+ else
>+ virtio_mem_bbm_notify_cancel_offline(vm, id,
>+ mhp->start_pfn,
>+ mhp->nr_pages);
> vm->hotplug_active = false;
> mutex_unlock(&vm->hotplug_mutex);
> break;
>@@ -1189,7 +1230,13 @@ static void virtio_mem_online_page_cb(struct page *page, unsigned int order)
> do_online = virtio_mem_sbm_test_sb_plugged(vm, id,
> sb_id, 1);
> } else {
>- do_online = true;
>+ /*
>+ * If the whole block is marked fake offline, keep
>+ * everything that way.
>+ */
>+ id = virtio_mem_phys_to_bb_id(vm, addr);
>+ do_online = virtio_mem_bbm_get_bb_state(vm, id) !=
>+ VIRTIO_MEM_BBM_BB_FAKE_OFFLINE;
> }
> if (do_online)
> generic_online_page(page, order);
>@@ -1969,15 +2016,50 @@ static int virtio_mem_sbm_unplug_request(struct virtio_mem *vm, uint64_t diff)
> static int virtio_mem_bbm_offline_remove_and_unplug_bb(struct virtio_mem *vm,
> unsigned long bb_id)
> {
>+ const unsigned long start_pfn = PFN_DOWN(virtio_mem_bb_id_to_phys(vm, bb_id));
>+ const unsigned long nr_pages = PFN_DOWN(vm->bbm.bb_size);
>+ unsigned long end_pfn = start_pfn + nr_pages;
>+ unsigned long pfn;
>+ struct page *page;
> int rc;
>
> if (WARN_ON_ONCE(virtio_mem_bbm_get_bb_state(vm, bb_id) !=
> VIRTIO_MEM_BBM_BB_ADDED))
> return -EINVAL;
>
>+ if (bbm_safe_unplug) {
>+ /*
>+ * Start by fake-offlining all memory. Once we marked the device
>+ * block as fake-offline, all newly onlined memory will
>+ * automatically be kept fake-offline. Protect from concurrent
>+ * onlining/offlining until we have a consistent state.
>+ */
>+ mutex_lock(&vm->hotplug_mutex);
>+ virtio_mem_bbm_set_bb_state(vm, bb_id,
>+ VIRTIO_MEM_BBM_BB_FAKE_OFFLINE);
>+
State is set here.
>+ for (pfn = start_pfn; pfn < end_pfn; pfn += PAGES_PER_SECTION) {
>+ page = pfn_to_online_page(pfn);
>+ if (!page)
>+ continue;
>+
>+ rc = virtio_mem_fake_offline(pfn, PAGES_PER_SECTION);
>+ if (rc) {
>+ end_pfn = pfn;
>+ goto rollback_safe_unplug;
>+ }
>+ }
>+ mutex_unlock(&vm->hotplug_mutex);
>+ }
>+
> rc = virtio_mem_bbm_offline_and_remove_bb(vm, bb_id);
>- if (rc)
>+ if (rc) {
>+ if (bbm_safe_unplug) {
>+ mutex_lock(&vm->hotplug_mutex);
>+ goto rollback_safe_unplug;
>+ }
> return rc;
>+ }
>
> rc = virtio_mem_bbm_unplug_bb(vm, bb_id);
> if (rc)
And changed to PLUGGED or UNUSED based on rc.
>@@ -1987,6 +2069,17 @@ static int virtio_mem_bbm_offline_remove_and_unplug_bb(struct virtio_mem *vm,
> virtio_mem_bbm_set_bb_state(vm, bb_id,
> VIRTIO_MEM_BBM_BB_UNUSED);
> return rc;
>+
>+rollback_safe_unplug:
>+ for (pfn = start_pfn; pfn < end_pfn; pfn += PAGES_PER_SECTION) {
>+ page = pfn_to_online_page(pfn);
>+ if (!page)
>+ continue;
>+ virtio_mem_fake_online(pfn, PAGES_PER_SECTION);
>+ }
>+ virtio_mem_bbm_set_bb_state(vm, bb_id, VIRTIO_MEM_BBM_BB_ADDED);
And changed to ADDED if failed.
>+ mutex_unlock(&vm->hotplug_mutex);
>+ return rc;
> }
So in which case, the bbm state is FAKE_OFFLINE during
virtio_mem_bbm_notify_going_offline() and
virtio_mem_bbm_notify_cancel_offline() ?
>
> /*
>--
>2.26.2
--
Wei Yang
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