* Re: [PATCH v2] DAX: warn when kmem regions are truncated for memory block alignment.
2025-04-02 1:59 [PATCH v2] DAX: warn when kmem regions are truncated for memory block alignment Gregory Price
@ 2025-04-02 7:58 ` David Hildenbrand
2025-04-04 13:45 ` Jonathan Cameron
` (2 subsequent siblings)
3 siblings, 0 replies; 6+ messages in thread
From: David Hildenbrand @ 2025-04-02 7:58 UTC (permalink / raw)
To: Gregory Price, linux-cxl
Cc: nvdimm, linux-kernel, kernel-team, dan.j.williams, vishal.l.verma,
dave.jiang
On 02.04.25 03:59, Gregory Price wrote:
> Device capacity intended for use as system ram should be aligned to the
> archite-defined memory block size or that capacity will be silently
> truncated and capacity stranded.
>
> As hotplug dax memory becomes more prevelant, the memory block size
> alignment becomes more important for platform and device vendors to
> pay attention to - so this truncation should not be silent.
>
> This issue is particularly relevant for CXL Dynamic Capacity devices,
> whose capacity may arrive in spec-aligned but block-misaligned chunks.
>
> Suggested-by: David Hildenbrand <david@redhat.com>
> Suggested-by: Dan Williams <dan.j.williams@intel.com>
> Signed-off-by: Gregory Price <gourry@gourry.net>
> ---
> drivers/dax/kmem.c | 10 +++++++++-
> 1 file changed, 9 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/dax/kmem.c b/drivers/dax/kmem.c
> index e97d47f42ee2..32fe3215e11e 100644
> --- a/drivers/dax/kmem.c
> +++ b/drivers/dax/kmem.c
> @@ -13,6 +13,7 @@
> #include <linux/mman.h>
> #include <linux/memory-tiers.h>
> #include <linux/memory_hotplug.h>
> +#include <linux/string_helpers.h>
> #include "dax-private.h"
> #include "bus.h"
>
> @@ -68,7 +69,7 @@ static void kmem_put_memory_types(void)
> static int dev_dax_kmem_probe(struct dev_dax *dev_dax)
> {
> struct device *dev = &dev_dax->dev;
> - unsigned long total_len = 0;
> + unsigned long total_len = 0, orig_len = 0;
> struct dax_kmem_data *data;
> struct memory_dev_type *mtype;
> int i, rc, mapped = 0;
> @@ -97,6 +98,7 @@ static int dev_dax_kmem_probe(struct dev_dax *dev_dax)
> for (i = 0; i < dev_dax->nr_range; i++) {
> struct range range;
>
> + orig_len += range_len(&dev_dax->ranges[i].range);
> rc = dax_kmem_range(dev_dax, i, &range);
> if (rc) {
> dev_info(dev, "mapping%d: %#llx-%#llx too small after alignment\n",
> @@ -109,6 +111,12 @@ static int dev_dax_kmem_probe(struct dev_dax *dev_dax)
> if (!total_len) {
> dev_warn(dev, "rejecting DAX region without any memory after alignment\n");
> return -EINVAL;
> + } else if (total_len != orig_len) {
> + char buf[16];
> +
> + string_get_size((orig_len - total_len), 1, STRING_UNITS_2,
> + buf, sizeof(buf));
> + dev_warn(dev, "DAX region truncated by %s due to alignment\n", buf);
Acked-by: David Hildenbrand <david@redhat.com>
--
Cheers,
David / dhildenb
^ permalink raw reply [flat|nested] 6+ messages in thread* Re: [PATCH v2] DAX: warn when kmem regions are truncated for memory block alignment.
2025-04-02 1:59 [PATCH v2] DAX: warn when kmem regions are truncated for memory block alignment Gregory Price
2025-04-02 7:58 ` David Hildenbrand
@ 2025-04-04 13:45 ` Jonathan Cameron
2025-04-09 22:21 ` Alison Schofield
2025-04-09 23:43 ` Dan Williams
3 siblings, 0 replies; 6+ messages in thread
From: Jonathan Cameron @ 2025-04-04 13:45 UTC (permalink / raw)
To: Gregory Price
Cc: linux-cxl, nvdimm, linux-kernel, kernel-team, dan.j.williams,
vishal.l.verma, dave.jiang, David Hildenbrand
On Tue, 1 Apr 2025 21:59:20 -0400
Gregory Price <gourry@gourry.net> wrote:
> Device capacity intended for use as system ram should be aligned to the
> archite-defined memory block size or that capacity will be silently
archite?
> truncated and capacity stranded.
>
> As hotplug dax memory becomes more prevelant, the memory block size
> alignment becomes more important for platform and device vendors to
> pay attention to - so this truncation should not be silent.
>
> This issue is particularly relevant for CXL Dynamic Capacity devices,
> whose capacity may arrive in spec-aligned but block-misaligned chunks.
>
> Suggested-by: David Hildenbrand <david@redhat.com>
> Suggested-by: Dan Williams <dan.j.williams@intel.com>
> Signed-off-by: Gregory Price <gourry@gourry.net>
One trivial comment inline otherwise seems reasonable to me.
Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
> ---
> drivers/dax/kmem.c | 10 +++++++++-
> 1 file changed, 9 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/dax/kmem.c b/drivers/dax/kmem.c
> index e97d47f42ee2..32fe3215e11e 100644
> --- a/drivers/dax/kmem.c
> +++ b/drivers/dax/kmem.c
> @@ -13,6 +13,7 @@
> #include <linux/mman.h>
> #include <linux/memory-tiers.h>
> #include <linux/memory_hotplug.h>
> +#include <linux/string_helpers.h>
> #include "dax-private.h"
> #include "bus.h"
>
> @@ -68,7 +69,7 @@ static void kmem_put_memory_types(void)
> static int dev_dax_kmem_probe(struct dev_dax *dev_dax)
> {
> struct device *dev = &dev_dax->dev;
> - unsigned long total_len = 0;
> + unsigned long total_len = 0, orig_len = 0;
> struct dax_kmem_data *data;
> struct memory_dev_type *mtype;
> int i, rc, mapped = 0;
> @@ -97,6 +98,7 @@ static int dev_dax_kmem_probe(struct dev_dax *dev_dax)
> for (i = 0; i < dev_dax->nr_range; i++) {
> struct range range;
>
> + orig_len += range_len(&dev_dax->ranges[i].range);
> rc = dax_kmem_range(dev_dax, i, &range);
> if (rc) {
> dev_info(dev, "mapping%d: %#llx-%#llx too small after alignment\n",
> @@ -109,6 +111,12 @@ static int dev_dax_kmem_probe(struct dev_dax *dev_dax)
> if (!total_len) {
> dev_warn(dev, "rejecting DAX region without any memory after alignment\n");
> return -EINVAL;
> + } else if (total_len != orig_len) {
> + char buf[16];
> +
> + string_get_size((orig_len - total_len), 1, STRING_UNITS_2,
Trivial but do those inner brackets really add anything?
> + buf, sizeof(buf));
> + dev_warn(dev, "DAX region truncated by %s due to alignment\n", buf);
> }
>
> init_node_memory_type(numa_node, mtype);
^ permalink raw reply [flat|nested] 6+ messages in thread* Re: [PATCH v2] DAX: warn when kmem regions are truncated for memory block alignment.
2025-04-02 1:59 [PATCH v2] DAX: warn when kmem regions are truncated for memory block alignment Gregory Price
2025-04-02 7:58 ` David Hildenbrand
2025-04-04 13:45 ` Jonathan Cameron
@ 2025-04-09 22:21 ` Alison Schofield
2025-04-09 22:48 ` Gregory Price
2025-04-09 23:43 ` Dan Williams
3 siblings, 1 reply; 6+ messages in thread
From: Alison Schofield @ 2025-04-09 22:21 UTC (permalink / raw)
To: Gregory Price
Cc: linux-cxl, nvdimm, linux-kernel, kernel-team, dan.j.williams,
vishal.l.verma, dave.jiang, David Hildenbrand
On Tue, Apr 01, 2025 at 09:59:20PM -0400, Gregory Price wrote:
> Device capacity intended for use as system ram should be aligned to the
> archite-defined memory block size or that capacity will be silently
> truncated and capacity stranded.
>
> As hotplug dax memory becomes more prevelant, the memory block size
> alignment becomes more important for platform and device vendors to
> pay attention to - so this truncation should not be silent.
>
> This issue is particularly relevant for CXL Dynamic Capacity devices,
> whose capacity may arrive in spec-aligned but block-misaligned chunks.
>
> Suggested-by: David Hildenbrand <david@redhat.com>
> Suggested-by: Dan Williams <dan.j.williams@intel.com>
> Signed-off-by: Gregory Price <gourry@gourry.net>
Existing unit test 'daxctl-devices.sh' hits this case:
[ 52.547521] kmem dax3.0: DAX region truncated by 62.0 MiB due to alignment
Tested-by: Alison Schofield <alison.schofield@intel.com>
snip
>
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [PATCH v2] DAX: warn when kmem regions are truncated for memory block alignment.
2025-04-09 22:21 ` Alison Schofield
@ 2025-04-09 22:48 ` Gregory Price
0 siblings, 0 replies; 6+ messages in thread
From: Gregory Price @ 2025-04-09 22:48 UTC (permalink / raw)
To: Alison Schofield
Cc: linux-cxl, nvdimm, linux-kernel, kernel-team, dan.j.williams,
vishal.l.verma, dave.jiang, David Hildenbrand
On Wed, Apr 09, 2025 at 03:21:53PM -0700, Alison Schofield wrote:
> Existing unit test 'daxctl-devices.sh' hits this case:
> [ 52.547521] kmem dax3.0: DAX region truncated by 62.0 MiB due to alignment
>
> Tested-by: Alison Schofield <alison.schofield@intel.com>
>
Thanks for testing, good to know there's an existing test for this
will respin w/ Jonathan's recommendations and tags.
~Gregory
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [PATCH v2] DAX: warn when kmem regions are truncated for memory block alignment.
2025-04-02 1:59 [PATCH v2] DAX: warn when kmem regions are truncated for memory block alignment Gregory Price
` (2 preceding siblings ...)
2025-04-09 22:21 ` Alison Schofield
@ 2025-04-09 23:43 ` Dan Williams
3 siblings, 0 replies; 6+ messages in thread
From: Dan Williams @ 2025-04-09 23:43 UTC (permalink / raw)
To: Gregory Price, linux-cxl
Cc: nvdimm, linux-kernel, kernel-team, dan.j.williams, vishal.l.verma,
dave.jiang, David Hildenbrand
Gregory Price wrote:
> Device capacity intended for use as system ram should be aligned to the
> archite-defined memory block size or that capacity will be silently
> truncated and capacity stranded.
>
> As hotplug dax memory becomes more prevelant, the memory block size
> alignment becomes more important for platform and device vendors to
> pay attention to - so this truncation should not be silent.
>
> This issue is particularly relevant for CXL Dynamic Capacity devices,
> whose capacity may arrive in spec-aligned but block-misaligned chunks.
>
> Suggested-by: David Hildenbrand <david@redhat.com>
> Suggested-by: Dan Williams <dan.j.williams@intel.com>
> Signed-off-by: Gregory Price <gourry@gourry.net>
The typo in the changelog was already noted, and this addresses all my
feedback so feel free to add:
Reviewed-by: Dan Williams <dan.j.williams@intel.com>
^ permalink raw reply [flat|nested] 6+ messages in thread