On Tue, Jan 26, 2016 at 08:26:24PM -0800, Dan Williams wrote: > On Tue, Jan 26, 2016 at 7:52 PM, Joonsoo Kim <iamjoonsoo.kim@xxxxxxx> wrote: > > 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.kim@xxxxxxx> 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.kim@xxxxxxx> 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. > > I agree in principle that finding a 32-bit compatible solution is > desirable, but it simply may not be feasible. Okay. > > For now, I'll help with auditing the existing bits so we can enumerate > the tradeoffs. Thanks! :) > Hmm, one tradeoff that comes to mind for 32-bit is sacrificing > ZONE_HIGHMEM, for ZONE_CMA. Are there configurations that need both > enabled? If a platform needs highmem it really should be using a > 64-bit kernel (if possible), desire for ZONE_CMA might be a nice > encouragement to lessen the prevalence of highmem. I guess that it's not possible. There are many systems that need both. I don't think deeply, but, there is another option for ZONE_CMA. It can share ZONE_MOVABLE because their chracteristic is roughly same in view of MM. I will think more. Thanks. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>