[PATCH 1/2] nvme: allow user toggling hmb usage

Keith Busch
2021-07-27T16:41:21Z

The NVMe host memory buffer may consume a non-negligable amount of
memory. Controllers are required to function without the host memory
buffer enabled, but with possibly degraded performance. Export a sysfs
property to toggle this feature on a per-device granularity so users may
choose to reclaim memory at the expense of storage performance.

Signed-off-by: Keith Busch <kbusch@kernel.org>
---
drivers/nvme/host/pci.c | 45 ++++++++++++++++++++++++++++++++++++++++-
1 file changed, 44 insertions(+), 1 deletion(-)

diff --git a/drivers/nvme/host/pci.c b/drivers/nvme/host/pci.c
index ac72386b1f2c..e8f3b32131d2 100644
--- a/drivers/nvme/host/pci.c
+++ b/drivers/nvme/host/pci.c
@@ -137,6 +137,7 @@ struct nvme_dev {
u32 cmbloc;
struct nvme_ctrl ctrl;
u32 last_ps;
+ bool hmb;

mempool_t *iod_mempool;

@@ -1896,7 +1897,9 @@ static int nvme_set_host_mem(struct nvme_dev *dev, u32 bits)
dev_warn(dev->ctrl.device,
"failed to set host mem (err %d, flags %#x).\n",
ret, bits);
- }
+ } else
+ dev->hmb = bits & NVME_HOST_MEM_ENABLE;
+
return ret;
}

@@ -2081,6 +2084,42 @@ static ssize_t cmbsz_show(struct device *dev, struct device_attribute *attr,
}
static DEVICE_ATTR_RO(cmbsz);

+static ssize_t hmb_show(struct device *dev, struct device_attribute *attr,
+ char *buf)
+{
+ struct nvme_dev *ndev = to_nvme_dev(dev_get_drvdata(dev));
+
+ return sysfs_emit(buf, "%d\n", ndev->hmb);
+}
+
+static ssize_t hmb_store(struct device *dev, struct device_attribute *attr,
+ const char *buf, size_t count)
+{
+ struct nvme_dev *ndev = to_nvme_dev(dev_get_drvdata(dev));
+ bool new;
+ int ret;
+
+ if (strtobool(buf, &new) < 0)
+ return -EINVAL;
+
+ if (new == ndev->hmb)
+ return count;
+
+ if (new) {
+ ret = nvme_setup_host_mem(ndev);
+ } else {
+ ret = nvme_set_host_mem(ndev, 0);
+ if (!ret)
+ nvme_free_host_mem(ndev);
+ }
+
+ if (ret < 0)
+ return ret;
+
+ return count;
+}
+static DEVICE_ATTR_RW(hmb);
+
static umode_t nvme_pci_attrs_are_visible(struct kobject *kobj,
struct attribute *a, int n)
{
@@ -2094,6 +2133,9 @@ static umode_t nvme_pci_attrs_are_visible(struct kobject *kobj,
if (!dev->cmbsz)
return 0;
}
+ if (a == &dev_attr_hmb.attr && !ctrl->hmpre)
+ return 0;
+
return a->mode;
}

@@ -2101,6 +2143,7 @@ static struct attribute *nvme_pci_attrs[] = {
&dev_attr_cmb.attr,
&dev_attr_cmbloc.attr,
&dev_attr_cmbsz.attr,
+ &dev_attr_hmb.attr,
NULL,
};

--
2.25.4