Re: [PATCH 5/5] dax: "Hotplug" persistent memory for use like normal RAM

[Brice Goglin <Brice.Goglin@inria.fr>]

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Le 25/01/2019 à 00:14, Dave Hansen a écrit :
> From: Dave Hansen <dave.hansen@linux.intel.com>
>
> This is intended for use with NVDIMMs that are physically persistent
> (physically like flash) so that they can be used as a cost-effective
> RAM replacement.  Intel Optane DC persistent memory is one
> implementation of this kind of NVDIMM.
>
> Currently, a persistent memory region is "owned" by a device driver,
> either the "Direct DAX" or "Filesystem DAX" drivers.  These drivers
> allow applications to explicitly use persistent memory, generally
> by being modified to use special, new libraries. (DIMM-based
> persistent memory hardware/software is described in great detail
> here: Documentation/nvdimm/nvdimm.txt).
>
> However, this limits persistent memory use to applications which
> *have* been modified.  To make it more broadly usable, this driver
> "hotplugs" memory into the kernel, to be managed and used just like
> normal RAM would be.
>
> To make this work, management software must remove the device from
> being controlled by the "Device DAX" infrastructure:
>
> 	echo -n dax0.0 > /sys/bus/dax/drivers/device_dax/remove_id
> 	echo -n dax0.0 > /sys/bus/dax/drivers/device_dax/unbind


Hello Dave

I am trying to use these patches (on top on Dan's nvdimm-pending branch
with Keith's HMAT patches). Writing to remove_id just hangs. echo never
returns, it uses 100% CPU and I can't kill it.

[ 5468.744898] bash            R  running task        0 21419  21416 0x00000080
[ 5468.744899] Call Trace:
[ 5468.744902]  ? vsnprintf+0x372/0x4e0
[ 5468.744904]  ? klist_next+0x79/0xe0
[ 5468.744905]  ? sprintf+0x56/0x80
[ 5468.744907]  ? bus_for_each_dev+0x8a/0xc0
[ 5468.744911]  ? do_id_store+0xe8/0x1e0
[ 5468.744914]  ? _cond_resched+0x15/0x30
[ 5468.744915]  ? __kmalloc+0x17f/0x200
[ 5468.744918]  ? kernfs_fop_write+0x83/0x190
[ 5468.744918]  ? __vfs_write+0x36/0x1b0
[ 5468.744919]  ? selinux_file_permission+0xe1/0x130
[ 5468.744921]  ? security_file_permission+0x36/0x100
[ 5468.744922]  ? vfs_write+0xad/0x1b0
[ 5468.744922]  ? ksys_write+0x52/0xc0
[ 5468.744924]  ? do_syscall_64+0x5b/0x180
[ 5468.744927]  ? entry_SYSCALL_64_after_hwframe+0x44/0xa9

CONFIG_NVDIMM_DAX=y
CONFIG_DAX_DRIVER=y
CONFIG_DAX=y
CONFIG_DEV_DAX=m
CONFIG_DEV_DAX_PMEM=m
CONFIG_DEV_DAX_KMEM=m
CONFIG_DEV_DAX_PMEM_COMPAT=m
CONFIG_FS_DAX=y
CONFIG_FS_DAX_PMD=y

  {
    "dev":"namespace0.0",
    "mode":"devdax",
    "map":"dev",
    "size":1598128390144,
    "uuid":"7046a749-477f-4690-9b3c-a640a1aa44f1",
    "chardev":"dax0.0"
  }


I've used your patches on fake hardware (memmap=xx!yy) with an older
nvdimm-pending branch (without Keith's patches). It worked fine. This
time I am running on real Intel hardware. Any idea where to look ?

Thanks

Brice



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