On Wed, 27 Jan 2016 22:19:14 -0800 Dan Williams <dan.j.williams@xxxxxxxxx> wrote: > ZONE_DEVICE (merged in 4.3) and ZONE_CMA (proposed) are examples of new > mm zones that are bumping up against the current maximum limit of 4 > zones, i.e. 2 bits in page->flags. When adding a zone this equation > still needs to be satisified: > > SECTIONS_WIDTH + ZONES_WIDTH + NODES_SHIFT + LAST_CPUPID_SHIFT > <= BITS_PER_LONG - NR_PAGEFLAGS > > ZONE_DEVICE currently tries to satisfy this equation by requiring that > ZONE_DMA be disabled, but this is untenable given generic kernels want > to support ZONE_DEVICE and ZONE_DMA simultaneously. ZONE_CMA would like > to increase the amount of memory covered per section, but that limits > the minimum granularity at which consecutive memory ranges can be added > via devm_memremap_pages(). > > The trade-off of what is acceptable to sacrifice depends heavily on the > platform. For example, ZONE_CMA is targeted for 32-bit platforms where > page->flags is constrained, but those platforms likely do not care about > the minimum granularity of memory hotplug. A big iron machine with 1024 > numa nodes can likely sacrifice ZONE_DMA where a general purpose > distribution kernel can not. > > CONFIG_NR_ZONES_EXTENDED is a configuration symbol that gets selected > when the number of configured zones exceeds 4. It documents the > configuration symbols and definitions that get modified when ZONES_WIDTH > is greater than 2. > > For now, it steals a bit from NODES_SHIFT. Later on it can be used to > document the definitions that get modified when a 32-bit configuration > wants more zone bits. So if you want ZONE_DMA, you're limited to 512 NUMA nodes? That seems reasonable. > --- a/arch/x86/Kconfig > +++ b/arch/x86/Kconfig > @@ -1409,8 +1409,10 @@ config NUMA_EMU > > config NODES_SHIFT > int "Maximum NUMA Nodes (as a power of 2)" if !MAXSMP > - range 1 10 > - default "10" if MAXSMP > + range 1 10 if !NR_ZONES_EXTENDED > + range 1 9 if NR_ZONES_EXTENDED > + default "10" if MAXSMP && !NR_ZONES_EXTENDED > + default "9" if MAXSMP && NR_ZONES_EXTENDED > default "6" if X86_64 > default "3" > depends on NEED_MULTIPLE_NODES > diff --git a/include/linux/gfp.h b/include/linux/gfp.h > index 28ad5f6494b0..5979c2c80140 100644 > --- a/include/linux/gfp.h > +++ b/include/linux/gfp.h > @@ -329,22 +329,29 @@ static inline bool gfpflags_allow_blocking(const gfp_t gfp_flags) > * 0xe => BAD (MOVABLE+DMA32+HIGHMEM) > * 0xf => BAD (MOVABLE+DMA32+HIGHMEM+DMA) > * > - * ZONES_SHIFT must be <= 2 on 32 bit platforms. > + * GFP_ZONES_SHIFT must be <= 2 on 32 bit platforms. > */ > > -#if 16 * ZONES_SHIFT > BITS_PER_LONG > -#error ZONES_SHIFT too large to create GFP_ZONE_TABLE integer > +#if defined(CONFIG_ZONE_DEVICE) && (MAX_NR_ZONES-1) <= 4 > +/* ZONE_DEVICE is not a valid GFP zone specifier */ > +#define GFP_ZONES_SHIFT 2 > +#else > +#define GFP_ZONES_SHIFT ZONES_SHIFT > +#endif > + > +#if 16 * GFP_ZONES_SHIFT > BITS_PER_LONG > +#error GFP_ZONES_SHIFT too large to create GFP_ZONE_TABLE integer > #endif > > #define GFP_ZONE_TABLE ( \ > - (ZONE_NORMAL << 0 * ZONES_SHIFT) \ > - | (OPT_ZONE_DMA << ___GFP_DMA * ZONES_SHIFT) \ > - | (OPT_ZONE_HIGHMEM << ___GFP_HIGHMEM * ZONES_SHIFT) \ > - | (OPT_ZONE_DMA32 << ___GFP_DMA32 * ZONES_SHIFT) \ > - | (ZONE_NORMAL << ___GFP_MOVABLE * ZONES_SHIFT) \ > - | (OPT_ZONE_DMA << (___GFP_MOVABLE | ___GFP_DMA) * ZONES_SHIFT) \ > - | (ZONE_MOVABLE << (___GFP_MOVABLE | ___GFP_HIGHMEM) * ZONES_SHIFT) \ > - | (OPT_ZONE_DMA32 << (___GFP_MOVABLE | ___GFP_DMA32) * ZONES_SHIFT) \ > + (ZONE_NORMAL << 0 * GFP_ZONES_SHIFT) \ > + | (OPT_ZONE_DMA << ___GFP_DMA * GFP_ZONES_SHIFT) \ > + | (OPT_ZONE_HIGHMEM << ___GFP_HIGHMEM * GFP_ZONES_SHIFT) \ > + | (OPT_ZONE_DMA32 << ___GFP_DMA32 * GFP_ZONES_SHIFT) \ > + | (ZONE_NORMAL << ___GFP_MOVABLE * GFP_ZONES_SHIFT) \ > + | (OPT_ZONE_DMA << (___GFP_MOVABLE | ___GFP_DMA) * GFP_ZONES_SHIFT) \ > + | (ZONE_MOVABLE << (___GFP_MOVABLE | ___GFP_HIGHMEM) * GFP_ZONES_SHIFT) \ > + | (OPT_ZONE_DMA32 << (___GFP_MOVABLE | ___GFP_DMA32) * GFP_ZONES_SHIFT) \ > ) Geeze. Congrats on decrypting this stuff. I hope. Do you think it's possible to comprehensibly document it all for the next poor soul who ventures into it? -- 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>