| Message ID | 20190420153148.21548-3-pasha.tatashin@soleen.com (mailing list archive) |
|---|---|
| State | Superseded |
| Headers | show |
| Series | "Hotremove" persistent memory | expand |
On Sat, Apr 20, 2019 at 8:36 AM Pavel Tatashin <pasha.tatashin@soleen.com> wrote: > > It is now allowed to use persistent memory like a regular RAM, but > currently there is no way to remove this memory until machine is > rebooted. > > This work expands the functionality to also allow hot removing > previously hotplugged persistent memory, and recover the device for use > for other purposes. > > To hotremove persistent memory, the management software must unbind it > from device-dax/kmem driver: > > echo dax0.0 > /sys/bus/dax/drivers/kmem/unbind > > Signed-off-by: Pavel Tatashin <pasha.tatashin@soleen.com> > --- > drivers/dax/dax-private.h | 2 + > drivers/dax/kmem.c | 77 +++++++++++++++++++++++++++++++++++++-- > 2 files changed, 75 insertions(+), 4 deletions(-) > > diff --git a/drivers/dax/dax-private.h b/drivers/dax/dax-private.h > index a45612148ca0..999aaf3a29b3 100644 > --- a/drivers/dax/dax-private.h > +++ b/drivers/dax/dax-private.h > @@ -53,6 +53,7 @@ struct dax_region { > * @pgmap - pgmap for memmap setup / lifetime (driver owned) > * @ref: pgmap reference count (driver owned) > * @cmp: @ref final put completion (driver owned) > + * @dax_mem_res: physical address range of hotadded DAX memory > */ > struct dev_dax { > struct dax_region *region; > @@ -62,6 +63,7 @@ struct dev_dax { > struct dev_pagemap pgmap; > struct percpu_ref ref; > struct completion cmp; > + struct resource *dax_kmem_res; > }; > > static inline struct dev_dax *to_dev_dax(struct device *dev) > diff --git a/drivers/dax/kmem.c b/drivers/dax/kmem.c > index 4c0131857133..026c34f93df5 100644 > --- a/drivers/dax/kmem.c > +++ b/drivers/dax/kmem.c > @@ -71,21 +71,90 @@ int dev_dax_kmem_probe(struct device *dev) > kfree(new_res); > return rc; > } > + dev_dax->dax_kmem_res = new_res; > > return 0; > } > > +#ifdef CONFIG_MEMORY_HOTREMOVE > +/* > + * Offline device-dax's memory_blocks. If a memory_block cannot be offlined > + * a warning is printed and an error is returned. dax hotremove can succeed > + * only when every memory_block is offline. > + */ > +static int > +offline_memblock_cb(struct memory_block *mem, void *arg) > +{ > + struct device *dev = (struct device *)arg; > + int rc = device_offline(&mem->dev); > + > + if (rc < 0) { > + unsigned long spfn = section_nr_to_pfn(mem->start_section_nr); > + unsigned long epfn = section_nr_to_pfn(mem->end_section_nr); > + phys_addr_t spa = spfn << PAGE_SHIFT; > + phys_addr_t epa = epfn << PAGE_SHIFT; > + > + dev_warn(dev, "could not offline memory block [%pa-%pa]\n", > + &spa, &epa); > + > + return rc; > + } > + > + return 0; > +} > + > +static int dev_dax_kmem_remove(struct device *dev) > +{ > + struct dev_dax *dev_dax = to_dev_dax(dev); > + struct resource *res = dev_dax->dax_kmem_res; > + resource_size_t kmem_start; > + resource_size_t kmem_size; > + unsigned long start_pfn; > + unsigned long end_pfn; > + int rc; > + > + /* > + * dax kmem resource does not exist, means memory was never hotplugged. > + * So, nothing to do here. > + */ > + if (!res) > + return 0; > + > + kmem_start = res->start; > + kmem_size = resource_size(res); > + start_pfn = kmem_start >> PAGE_SHIFT; > + end_pfn = start_pfn + (kmem_size >> PAGE_SHIFT) - 1; > + > + /* Walk and offline every singe memory_block of the dax region. */ > + lock_device_hotplug(); > + rc = walk_memory_range(start_pfn, end_pfn, dev, offline_memblock_cb); > + unlock_device_hotplug(); > + if (rc) > + return rc; This potential early return is the reason why memory hotremove is not reliable vs the driver-core. If this walk fails to offline the memory it will still be online, but the driver-core has no consideration for device-unbind failing. The ubind will proceed while the memory stays pinned.
> > + > > + /* Walk and offline every singe memory_block of the dax region. */ > > + lock_device_hotplug(); > > + rc = walk_memory_range(start_pfn, end_pfn, dev, offline_memblock_cb); > > + unlock_device_hotplug(); > > + if (rc) > > + return rc; > > This potential early return is the reason why memory hotremove is not > reliable vs the driver-core. If this walk fails to offline the memory > it will still be online, but the driver-core has no consideration for > device-unbind failing. The ubind will proceed while the memory stays > pinned. Hi Dan, Thank you for looking at this. Are you saying, that if drv.remove() returns a failure it is simply ignored, and unbind proceeds? Pasha
On Sat, Apr 20, 2019 at 9:30 AM Pavel Tatashin <pasha.tatashin@soleen.com> wrote: > > > > + > > > + /* Walk and offline every singe memory_block of the dax region. */ > > > + lock_device_hotplug(); > > > + rc = walk_memory_range(start_pfn, end_pfn, dev, offline_memblock_cb); > > > + unlock_device_hotplug(); > > > + if (rc) > > > + return rc; > > > > This potential early return is the reason why memory hotremove is not > > reliable vs the driver-core. If this walk fails to offline the memory > > it will still be online, but the driver-core has no consideration for > > device-unbind failing. The ubind will proceed while the memory stays > > pinned. > > Hi Dan, > > Thank you for looking at this. Are you saying, that if drv.remove() > returns a failure it is simply ignored, and unbind proceeds? Yeah, that's the problem. I've looked at making unbind able to fail, but that can lead to general bad behavior in device-drivers. I.e. why spend time unwinding allocated resources when the driver can simply fail unbind? About the best a driver can do is make unbind wait on some event, but any return results in device-unbind.
> > Thank you for looking at this. Are you saying, that if drv.remove() > > returns a failure it is simply ignored, and unbind proceeds? > > Yeah, that's the problem. I've looked at making unbind able to fail, > but that can lead to general bad behavior in device-drivers. I.e. why > spend time unwinding allocated resources when the driver can simply > fail unbind? About the best a driver can do is make unbind wait on > some event, but any return results in device-unbind. Hm, just tested, and it is indeed so. I see the following options: 1. Move hot remove code to some other interface, that can fail. Not sure what that would be, but outside of unbind/remove_id. Any suggestion? 2. Option two is don't attept to offline memory in unbind. Do hot-remove memory in unbind if every section is already offlined. Basically, do a walk through memblocks, and if every section is offlined, also do the cleanup. Pasha
On Sat, Apr 20, 2019 at 10:02 AM Pavel Tatashin <pasha.tatashin@soleen.com> wrote: > > > > Thank you for looking at this. Are you saying, that if drv.remove() > > > returns a failure it is simply ignored, and unbind proceeds? > > > > Yeah, that's the problem. I've looked at making unbind able to fail, > > but that can lead to general bad behavior in device-drivers. I.e. why > > spend time unwinding allocated resources when the driver can simply > > fail unbind? About the best a driver can do is make unbind wait on > > some event, but any return results in device-unbind. > > Hm, just tested, and it is indeed so. > > I see the following options: > > 1. Move hot remove code to some other interface, that can fail. Not > sure what that would be, but outside of unbind/remove_id. Any > suggestion? > 2. Option two is don't attept to offline memory in unbind. Do > hot-remove memory in unbind if every section is already offlined. > Basically, do a walk through memblocks, and if every section is > offlined, also do the cleanup. I think something like option-2 could work just as long as the user is ok with failure and prepared to handle it. It's already the case that the request_region() in kmem permanently prevents the memory range from being reused by any other driver. So if the hot-unplug fails it could skip the corresponding release_region() and effectively it's the same as what we have now in terms of reuse protection. In your flow if the memory remove failed then the conversion attempt from devdax to raw mode would also fail and presumably you could fall back to doing a full reboot / rebuild of the application state?
On Sat, Apr 20, 2019 at 5:02 PM Dan Williams <dan.j.williams@intel.com> wrote: > > On Sat, Apr 20, 2019 at 10:02 AM Pavel Tatashin > <pasha.tatashin@soleen.com> wrote: > > > > > > Thank you for looking at this. Are you saying, that if drv.remove() > > > > returns a failure it is simply ignored, and unbind proceeds? > > > > > > Yeah, that's the problem. I've looked at making unbind able to fail, > > > but that can lead to general bad behavior in device-drivers. I.e. why > > > spend time unwinding allocated resources when the driver can simply > > > fail unbind? About the best a driver can do is make unbind wait on > > > some event, but any return results in device-unbind. > > > > Hm, just tested, and it is indeed so. > > > > I see the following options: > > > > 1. Move hot remove code to some other interface, that can fail. Not > > sure what that would be, but outside of unbind/remove_id. Any > > suggestion? > > 2. Option two is don't attept to offline memory in unbind. Do > > hot-remove memory in unbind if every section is already offlined. > > Basically, do a walk through memblocks, and if every section is > > offlined, also do the cleanup. > > I think something like option-2 could work just as long as the user is > ok with failure and prepared to handle it. It's already the case that > the request_region() in kmem permanently prevents the memory range > from being reused by any other driver. So if the hot-unplug fails it > could skip the corresponding release_region() and effectively it's the > same as what we have now in terms of reuse protection. In your flow if > the memory remove failed then the conversion attempt from devdax to > raw mode would also fail and presumably you could fall back to doing a > full reboot / rebuild of the application state? With option two, where we will simply check that every memory_block is offlined, we will have deterministic behavior: 1. If user did not offline every dax memory section beforehand via echo offline > /sys/devices/system/memory/memoryN/state echo dax0.0 > /sys/bus/dax/drivers/kmem/unbind Will be the same as now, will simply return, and user won't be able to use dax afterwords or hotremove it. 2. If user did offline ever dax memory section beforehand echo dax0.0 > /sys/bus/dax/drivers/kmem/unbind Will be guaranteed to succeed to hotremove the memory, as there is nothing that can fail. So, if user wants to hotremove dax memory, he/she must ensure that every section is offlined before unbinding. Pasha
On Sat, Apr 20, 2019 at 3:04 PM Pavel Tatashin <pasha.tatashin@soleen.com> wrote: > > On Sat, Apr 20, 2019 at 5:02 PM Dan Williams <dan.j.williams@intel.com> wrote: > > > > On Sat, Apr 20, 2019 at 10:02 AM Pavel Tatashin > > <pasha.tatashin@soleen.com> wrote: > > > > > > > > Thank you for looking at this. Are you saying, that if drv.remove() > > > > > returns a failure it is simply ignored, and unbind proceeds? > > > > > > > > Yeah, that's the problem. I've looked at making unbind able to fail, > > > > but that can lead to general bad behavior in device-drivers. I.e. why > > > > spend time unwinding allocated resources when the driver can simply > > > > fail unbind? About the best a driver can do is make unbind wait on > > > > some event, but any return results in device-unbind. > > > > > > Hm, just tested, and it is indeed so. > > > > > > I see the following options: > > > > > > 1. Move hot remove code to some other interface, that can fail. Not > > > sure what that would be, but outside of unbind/remove_id. Any > > > suggestion? > > > 2. Option two is don't attept to offline memory in unbind. Do > > > hot-remove memory in unbind if every section is already offlined. > > > Basically, do a walk through memblocks, and if every section is > > > offlined, also do the cleanup. > > > > I think something like option-2 could work just as long as the user is > > ok with failure and prepared to handle it. It's already the case that > > the request_region() in kmem permanently prevents the memory range > > from being reused by any other driver. So if the hot-unplug fails it > > could skip the corresponding release_region() and effectively it's the > > same as what we have now in terms of reuse protection. In your flow if > > the memory remove failed then the conversion attempt from devdax to > > raw mode would also fail and presumably you could fall back to doing a > > full reboot / rebuild of the application state? > > With option two, where we will simply check that every memory_block is > offlined, we will have deterministic behavior: > > 1. If user did not offline every dax memory section beforehand via > echo offline > /sys/devices/system/memory/memoryN/state > > echo dax0.0 > /sys/bus/dax/drivers/kmem/unbind > Will be the same as now, will simply return, and user won't be able to > use dax afterwords or hotremove it. > > 2. If user did offline ever dax memory section beforehand > echo dax0.0 > /sys/bus/dax/drivers/kmem/unbind > Will be guaranteed to succeed to hotremove the memory, as there is > nothing that can fail. > > So, if user wants to hotremove dax memory, he/she must ensure that > every section is offlined before unbinding. Sounds reasonable to me.
diff --git a/drivers/dax/dax-private.h b/drivers/dax/dax-private.h index a45612148ca0..999aaf3a29b3 100644 --- a/drivers/dax/dax-private.h +++ b/drivers/dax/dax-private.h @@ -53,6 +53,7 @@ struct dax_region { * @pgmap - pgmap for memmap setup / lifetime (driver owned) * @ref: pgmap reference count (driver owned) * @cmp: @ref final put completion (driver owned) + * @dax_mem_res: physical address range of hotadded DAX memory */ struct dev_dax { struct dax_region *region; @@ -62,6 +63,7 @@ struct dev_dax { struct dev_pagemap pgmap; struct percpu_ref ref; struct completion cmp; + struct resource *dax_kmem_res; }; static inline struct dev_dax *to_dev_dax(struct device *dev) diff --git a/drivers/dax/kmem.c b/drivers/dax/kmem.c index 4c0131857133..026c34f93df5 100644 --- a/drivers/dax/kmem.c +++ b/drivers/dax/kmem.c @@ -71,21 +71,90 @@ int dev_dax_kmem_probe(struct device *dev) kfree(new_res); return rc; } + dev_dax->dax_kmem_res = new_res; return 0; } +#ifdef CONFIG_MEMORY_HOTREMOVE +/* + * Offline device-dax's memory_blocks. If a memory_block cannot be offlined + * a warning is printed and an error is returned. dax hotremove can succeed + * only when every memory_block is offline. + */ +static int +offline_memblock_cb(struct memory_block *mem, void *arg) +{ + struct device *dev = (struct device *)arg; + int rc = device_offline(&mem->dev); + + if (rc < 0) { + unsigned long spfn = section_nr_to_pfn(mem->start_section_nr); + unsigned long epfn = section_nr_to_pfn(mem->end_section_nr); + phys_addr_t spa = spfn << PAGE_SHIFT; + phys_addr_t epa = epfn << PAGE_SHIFT; + + dev_warn(dev, "could not offline memory block [%pa-%pa]\n", + &spa, &epa); + + return rc; + } + + return 0; +} + +static int dev_dax_kmem_remove(struct device *dev) +{ + struct dev_dax *dev_dax = to_dev_dax(dev); + struct resource *res = dev_dax->dax_kmem_res; + resource_size_t kmem_start; + resource_size_t kmem_size; + unsigned long start_pfn; + unsigned long end_pfn; + int rc; + + /* + * dax kmem resource does not exist, means memory was never hotplugged. + * So, nothing to do here. + */ + if (!res) + return 0; + + kmem_start = res->start; + kmem_size = resource_size(res); + start_pfn = kmem_start >> PAGE_SHIFT; + end_pfn = start_pfn + (kmem_size >> PAGE_SHIFT) - 1; + + /* Walk and offline every singe memory_block of the dax region. */ + lock_device_hotplug(); + rc = walk_memory_range(start_pfn, end_pfn, dev, offline_memblock_cb); + unlock_device_hotplug(); + if (rc) + return rc; + + /* Hotremove memory, cannot fail because memory is already offlined */ + remove_memory(dev_dax->target_node, kmem_start, kmem_size); + + /* Release and free dax resources */ + release_resource(res); + kfree(res); + dev_dax->dax_kmem_res = NULL; + + return 0; +} +#else static int dev_dax_kmem_remove(struct device *dev) { /* - * Purposely leak the request_mem_region() for the device-dax - * range and return '0' to ->remove() attempts. The removal of - * the device from the driver always succeeds, but the region - * is permanently pinned as reserved by the unreleased + * Without hotremove purposely leak the request_mem_region() for the + * device-dax range and return '0' to ->remove() attempts. The removal + * of the device from the driver always succeeds, but the region is + * permanently pinned as reserved by the unreleased * request_mem_region(). */ return 0; } +#endif /* CONFIG_MEMORY_HOTREMOVE */ static struct dax_device_driver device_dax_kmem_driver = { .drv = {
It is now allowed to use persistent memory like a regular RAM, but currently there is no way to remove this memory until machine is rebooted. This work expands the functionality to also allow hot removing previously hotplugged persistent memory, and recover the device for use for other purposes. To hotremove persistent memory, the management software must unbind it from device-dax/kmem driver: echo dax0.0 > /sys/bus/dax/drivers/kmem/unbind Signed-off-by: Pavel Tatashin <pasha.tatashin@soleen.com> --- drivers/dax/dax-private.h | 2 + drivers/dax/kmem.c | 77 +++++++++++++++++++++++++++++++++++++-- 2 files changed, 75 insertions(+), 4 deletions(-)