On Tue, Jan 26, 2016 at 6:15 PM, Joonsoo Kim <iamjoonsoo....@lge.com> wrote: > On Tue, Jan 26, 2016 at 05:37:38PM -0800, Dan Williams wrote: >> On Tue, Jan 26, 2016 at 5:18 PM, Joonsoo Kim <iamjoonsoo....@lge.com> wrote: [..] >> > Please refer my previous attempt to add a new zone, ZONE_CMA. >> > >> > https://lkml.org/lkml/2015/2/12/84 >> > >> > It salvages a bit from SECTION_WIDTH by increasing section size. >> > Similarly, I guess we can reduce NODE_WIDTH if needed although >> > it could cause to reduce maximum node size. >> >> Dave pointed out to me that LAST__PID_SHIFT might be a better >> candidate to reduce to 7 bits. That field is for storing pids which >> are already bigger than 8 bits. If it is relying on the fact that >> pids don't rollover very often then likely the impact of 7-bits >> instead of 8 will be minimal. > > Hmm... I'm not sure it's possible or not, but, it looks not a general > solution. It will solve your problem because you are using 64 bit arch > but other 32 bit archs can't get the benefit.
This is where the ZONE_CMA and ZONE_DEVICE efforts diverge. ZONE_DEVICE is meant to enable DMA access to hundreds of gigagbytes of persistent memory. A 64-bit-only limitation for ZONE_DEVICE is reasonable.
