Re: [PATCH v2 00/10] Copy Offload in NVMe Fabrics with P2P PCI Memory

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

 





On 28/02/18 08:56 PM, Benjamin Herrenschmidt wrote:
On Thu, 2018-03-01 at 14:54 +1100, Benjamin Herrenschmidt wrote:
The problem is that acccording to him (I didn't double check the latest
patches) you effectively hotplug the PCIe memory into the system when
creating struct pages.

This cannot possibly work for us. First we cannot map PCIe memory as
cachable. (Note that doing so is a bad idea if you are behind a PLX
switch anyway since you'd ahve to manage cache coherency in SW).

Note: I think the above means it won't work behind a switch on x86
either, will it ?

This works perfectly fine on x86 behind a switch and we've tested it on multiple machines. We've never had an issue of running out of virtual space despite our PCI bars typically being located with an offset of 56TB or more. The arch code on x86 also somehow figures out not to map the memory as cachable so that's not an issue (though, at this point, the CPU never accesses the memory so even if it were, it wouldn't affect anything).

We also had this working on ARM64 a while back but it required some out of tree ZONE_DEVICE patches and some truly horrid hacks to it's arch code to ioremap the memory into the page map.

You didn't mention what architecture you were trying this on.

It may make sense at this point to make this feature dependent on x86 until more work is done to make it properly portable. Something like arch functions that allow adding IO memory pages to with a specific cache setting. Though, if an arch has such restrictive limits on the map size it would probably need to address that too somehow.

Thanks,

Logan



[Index of Archives]     [Linux RAID]     [Linux SCSI]     [Linux ATA RAID]     [IDE]     [Linux Wireless]     [Linux Kernel]     [ATH6KL]     [Linux Bluetooth]     [Linux Netdev]     [Kernel Newbies]     [Security]     [Git]     [Netfilter]     [Bugtraq]     [Yosemite News]     [MIPS Linux]     [ARM Linux]     [Linux Security]     [Device Mapper]

  Powered by Linux