On Tue, Jan 26, 2016 at 07:23:59PM -0800, Dan Williams wrote: > 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.
Yes, but, my point is that if someone need another zone like as ZONE_CMA, they couldn't get the benefit from this change. They need to re-investigate what bits they can reduce and need to re-do all things. If it is implemented more generally at this time, it can relieve their burden and less churn the code. It would be helpful for maintainability. Thanks.
