Gregory Price wrote: > On Mon, Feb 06, 2023 at 02:15:56PM -0800, Dan Williams wrote: > > Gregory Price wrote: > > > On Sun, Feb 05, 2023 at 05:04:05PM -0800, Dan Williams wrote: > > [..] > > > > > > Stupid question: when defaulting to online, do these devices get placed > > > into Zone Normal? Is there a way for us, at a minimum, to online this > > > as Zone Moveable in an effort to assist the "hope the kernel has not > > > pinned a page" problem (and to try to keep kernel resources out of this > > > zone in general). > > > > > > If this is covered by a different patch or already set up this way, > > > ignore me :] > > > > Have a look in Documentation/admin-guide/mm/memory-hotplug.rst, the > > 'daxctl recconfigure-device' man page and the the policy options of how > > hot-added memory is brought online. > > > > The routing can be anything from fully offline device-dax, to fully > > online ZONE_NORMAL, or even a mix of device-dax subdivision, > > ZONE_NORMAL, and ZONE_MOVABLE memblocks all within one CXL ram region. > > Hm. > > I'm just thinking, for early expander devices the assumption that the > default behavior should be auto-online is good. Just kinda working > through this in my head for multi-headed devices and early pools, and I > suppose the kernel paremeter covers that. Most of those will be used in > specialty, vertically integrated systems, so we're good to go. > > In the future when we get fully featured DCD's, I imagine we will have a > memory region of size X, with N memory blocks, but only some of those > blocks are online. I suppose it could also be done such that DCD capacity > add events drive the creation of new blocks under the region, as opposed > to having the region pre-create the blocks. In the case of DCD the proposal is "sparse" dax regions. So there will be nothing to online by default until extents start arriving. I do expect DCD systems will opt for memhp_default_state=offline so that userspace policy can be applied. > Either way I think the kernel parameter probably covers this case as > well, I'm just wondering if at some point the default will yet again > wish to be false, but i think that's a "CXL has become so successful all > memory is now CXL DCDs and computers look radically different" scenario. It's a distro policy. Fedora and RHEL, for example, pick different defaults.
