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Tsirkin" , David Hildenbrand , Pankaj Gupta , Jason Wang , Oscar Salvador , Igor Mammedov , Dave Young , Dan Williams , Pavel Tatashin , Stefan Hajnoczi , Vlastimil Babka Subject: [PATCH v4 04/15] virtio-mem: Paravirtualized memory hotunplug part 1 Date: Thu, 7 May 2020 16:01:28 +0200 Message-Id: <20200507140139.17083-5-david@redhat.com> In-Reply-To: <20200507140139.17083-1-david@redhat.com> References: <20200507140139.17083-1-david@redhat.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.79 on 10.5.11.12 Content-Transfer-Encoding: quoted-printable X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: Unplugging subblocks of memory blocks that are offline is easy. All we have to do is watch out for concurrent onlining activity. Tested-by: Pankaj Gupta Cc: "Michael S. Tsirkin" Cc: Jason Wang Cc: Oscar Salvador Cc: Michal Hocko Cc: Igor Mammedov Cc: Dave Young Cc: Andrew Morton Cc: Dan Williams Cc: Pavel Tatashin Cc: Stefan Hajnoczi Cc: Vlastimil Babka Signed-off-by: David Hildenbrand --- 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 270ddeaec059..a3ec795be8be 100644 --- a/drivers/virtio/virtio_mem.c +++ b/drivers/virtio/virtio_mem.c @@ -123,7 +123,7 @@ 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; @@ -280,6 +280,12 @@ static int virtio_mem_mb_state_prepare_next_mb(struc= t virtio_mem *vm) _mb_id++) \ if (virtio_mem_mb_get_state(_vm, _mb_id) =3D=3D _state) =20 +#define virtio_mem_for_each_mb_state_rev(_vm, _mb_id, _state) \ + for (_mb_id =3D _vm->next_mb_id - 1; \ + _mb_id >=3D _vm->first_mb_id && _vm->nb_mb_state[_state]; \ + _mb_id--) \ + if (virtio_mem_mb_get_state(_vm, _mb_id) =3D=3D _state) + /* * Mark all selected subblocks plugged. * @@ -325,6 +331,19 @@ static bool virtio_mem_mb_test_sb_plugged(struct vir= tio_mem *vm, bit + count; } =20 +/* + * 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 =3D (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) >=3D bit + count; +} + /* * Find the first plugged subblock. Returns vm->nb_sb_per_mb in case the= re is * none. @@ -513,6 +532,9 @@ static void virtio_mem_notify_offline(struct virtio_m= em *vm, BUG(); break; } + + /* trigger the workqueue, maybe we can now unplug memory. */ + virtio_mem_retry(vm); } =20 static void virtio_mem_notify_online(struct virtio_mem *vm, unsigned lon= g mb_id, @@ -1122,6 +1144,94 @@ static int virtio_mem_plug_request(struct virtio_m= em *vm, uint64_t diff) return rc; } =20 +/* + * Unplug the desired number of plugged subblocks of an offline memory b= lock. + * Will fail if any subblock cannot get unplugged (instead of skipping i= t). + * + * 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 =3D 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 =3D 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 dif= f) +{ + uint64_t nb_sb =3D 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 =3D 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 =3D 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 examp= le, * because the hypervisor was busy. @@ -1204,8 +1314,10 @@ static void virtio_mem_run_wq(struct work_struct *= work) if (vm->requested_size > vm->plugged_size) { diff =3D vm->requested_size - vm->plugged_size; rc =3D virtio_mem_plug_request(vm, diff); + } else { + diff =3D vm->plugged_size - vm->requested_size; + rc =3D virtio_mem_unplug_request(vm, diff); } - /* TODO: try to unplug memory */ } =20 switch (rc) { --=20 2.25.3