On Fri, Jul 10, 2026 at 05:44:58PM -0700, Dan Williams (nvidia) wrote:
> Gregory Price wrote:
> > On Thu, Jul 09, 2026 at 06:08:45PM -0400, Gregory Price wrote:
> > > On Thu, Jul 09, 2026 at 02:46:39PM -0700, Dan Williams (nvidia) wrote:
> > >
> > > This was more a matter of having the DEFAULT set consistently across
> > > the dax driver variant probe() functions to make the behavior explicit.
> > > I didn't want an un-set value bug to creep in here somehow.
> > >
> > > Happy to drop them if you think that's unneeded.
> > >
> >
> > Ah
> >
> > Not setting the value in each of those places is equivalent to setting
> > MMOP_OFFLINE (0), so better to just set DEFAULT regardless.
> >
> > So unless you have strong feelings i will keep them as-is.
>
> Right, the mild feelings are only coming from the changelog mismatch
> which says "Oh no, device-dax drivers can not specify their online type
> besides the default" and all this series does is keep the status quo.
>
> That can be had by just having unconditional:
>
> online_type = mhp_get_default_online_type();
>
> ...in dev_dax_kmem_probe() and get rid of dev_dax->online_type until the
> first user arrives. If you are respinning the series and that patch
> drops, yay. If not, oh well.
if you prefer, i can add the CXL build option to this series instead of
the follow up (attached). The code is fully contained in DAX anyway,
and I have it sitting off in another branch anyway.
I suppose with this, we can terminate the entire series and the first
user that grows an opinion can add the following:
cxl/cxl.h:
struct cxl_dax_region *cxlr_dax {
+ int online_type
};
dax/cxl.c:
data.online_type = (cxlr_dax.online_type == DAX_ONLINE_DEFAULT) ?
cxl_dax_online_type() : cxlr_dax.online_type;
~Gregory
>From b2cb5c4f5f03dd698df97ae3db2c0207db4acd83 Mon Sep 17 00:00:00 2001
From: Gregory Price <[email protected]>
Date: Thu, 9 Jul 2026 19:31:28 -0700
Subject: [PATCH] dax/cxl: add build-time CXL RAM region auto-online policy
CXL devices using kmem follow the single global auto-online policy.
On systems with multiple drivers using memory hotplug, this makes
management more complex - a single special kmem device forces all
kmem devices to be managed manually in userland.
Add a build-time option to select CXL device online policy.
- System default -> DAX_ONLINE_DEFAULT (default)
- Online -> MMOP_ONLINE
- Online (movable) -> MMOP_ONLINE_MOVABLE
- Online (kernel) -> MMOP_ONLINE_KERNEL
- Unplugged -> DAX_KMEM_UNPLUGGED
Default to system default to retain userland backward compatibility.
Signed-off-by: Gregory Price <[email protected]>
---
drivers/cxl/Kconfig | 41 +++++++++++++++++++++++++++++++++++++++++
drivers/dax/cxl.c | 15 ++++++++++++++-
2 files changed, 55 insertions(+), 1 deletion(-)
diff --git a/drivers/cxl/Kconfig b/drivers/cxl/Kconfig
index 80aeb0d556bd7..52450225dbb11 100644
--- a/drivers/cxl/Kconfig
+++ b/drivers/cxl/Kconfig
@@ -212,6 +212,47 @@ config CXL_REGION
If unsure say 'y'
+choice
+ prompt "CXL Memory Hotplug Policy"
+ depends on CXL_REGION
+ default CXL_MEMHP_POLICY_SYSTEM_DEFAULT
+ help
+ Select the online policy the CXL driver requests when a region is
+ hotplugged as System RAM.
+
+ If unsure, select "System default".
+
+config CXL_MEMHP_POLICY_SYSTEM_DEFAULT
+ bool "System default"
+ help
+ Follow the system-wide memory hotplug policy.
+
+config CXL_MEMHP_POLICY_ONLINE
+ bool "Online"
+ help
+ Automatically online memory and let the kernel choose the zone.
+
+config CXL_MEMHP_POLICY_ONLINE_MOVABLE
+ bool "Online (movable)"
+ help
+ Automatically online the memory into ZONE_MOVABLE. Choose this for
+ memory that may need to be hotremoved later, or if you do not want
+ unmovable, kernel allocations to land on this memory.
+
+config CXL_MEMHP_POLICY_ONLINE_KERNEL
+ bool "Online (kernel)"
+ help
+ Automatically online the memory into ZONE_NORMAL. The kernel may
+ place unmovable allocations on this memory.
+
+config CXL_MEMHP_POLICY_UNPLUGGED
+ bool "Unplugged"
+ help
+ Create the dax/kmem device but add no memory at bind time.
+ Choose this if a userland orchestrator will manage the device.
+
+endchoice
+
config CXL_REGION_INVALIDATION_TEST
bool "CXL: Region Cache Management Bypass (TEST)"
depends on CXL_REGION
diff --git a/drivers/dax/cxl.c b/drivers/dax/cxl.c
index 1a7ec62122134..15f70d578c22b 100644
--- a/drivers/dax/cxl.c
+++ b/drivers/dax/cxl.c
@@ -6,6 +6,19 @@
#include "../cxl/cxl.h"
#include "bus.h"
+static int cxl_dax_online_type(void)
+{
+ if (IS_ENABLED(CONFIG_CXL_MEMHP_POLICY_UNPLUGGED))
+ return DAX_KMEM_UNPLUGGED;
+ if (IS_ENABLED(CONFIG_CXL_MEMHP_POLICY_ONLINE))
+ return MMOP_ONLINE;
+ if (IS_ENABLED(CONFIG_CXL_MEMHP_POLICY_ONLINE_MOVABLE))
+ return MMOP_ONLINE_MOVABLE;
+ if (IS_ENABLED(CONFIG_CXL_MEMHP_POLICY_ONLINE_KERNEL))
+ return MMOP_ONLINE_KERNEL;
+ return DAX_ONLINE_DEFAULT;
+}
+
static int cxl_dax_region_probe(struct device *dev)
{
struct cxl_dax_region *cxlr_dax = to_cxl_dax_region(dev);
@@ -27,7 +40,7 @@ static int cxl_dax_region_probe(struct device *dev)
.id = -1,
.size = range_len(&cxlr_dax->hpa_range),
.memmap_on_memory = true,
- .online_type = DAX_ONLINE_DEFAULT,
+ .online_type = cxl_dax_online_type(),
};
return PTR_ERR_OR_ZERO(devm_create_dev_dax(&data));
--
2.53.0-Meta
