Re: [RFC][PATCH] drivers: base: dynamic memory block creation

[Seth Jennings <sjenning@linux.vnet.ibm.com>]

On Thu, Aug 15, 2013 at 02:01:09AM +0200, Rafael J. Wysocki wrote:
> On Wednesday, August 14, 2013 02:31:45 PM Seth Jennings wrote:
> > Large memory systems (~1TB or more) experience boot delays on the order
> > of minutes due to the initializing the memory configuration part of
> > sysfs at /sys/devices/system/memory/.
> > 
> > ppc64 has a normal memory block size of 256M (however sometimes as low
> > as 16M depending on the system LMB size), and (I think) x86 is 128M.  With
> > 1TB of RAM and a 256M block size, that's 4k memory blocks with 20 sysfs
> > entries per block that's around 80k items that need be created at boot
> > time in sysfs.  Some systems go up to 16TB where the issue is even more
> > severe.
> > 
> > This patch provides a means by which users can prevent the creation of
> > the memory block attributes at boot time, yet still dynamically create
> > them if they are needed.
> > 
> > This patch creates a new boot parameter, "largememory" that will prevent
> > memory_dev_init() from creating all of the memory block sysfs attributes
> > at boot time.  Instead, a new root attribute "show" will allow
> > the dynamic creation of the memory block devices.
> > Another new root attribute "present" shows the memory blocks present in
> > the system; the valid inputs for the "show" attribute.
> 
> I wonder how this is going to work with the ACPI device object binding to
> memory blocks that's in 3.11-rc.

Thanks for pointing this out.  Yes the walking of the memory blocks in
this code will present a problem for the dynamic creation of memory
blocks :/  Sounds like there are some other challenges (backward
compatibility, no boot paramater) that I'll have to look at as well.

Seth

> 
> That stuff will only work if the memory blocks are already there when
> acpi_memory_enable_device() runs and that is called from the ACPI namespace
> scanning code executed (1) during boot and (2) during hotplug.  So I don't
> think you can just create them on the fly at run time as a result of a
> sysfs write.
> 
> Thanks,
> Rafael
> 

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