On Fri, Mar 4, 2016 at 6:11 AM, Vlastimil Babka <vbabka@xxxxxxx> wrote: > On 03/02/2016 01:32 AM, Dan Williams 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 for the GFP_ZONE_TABLE. >> >> The GFP_ZONE_TABLE poses an interesting constraint since >> include/linux/gfp.h gets included by the 32-bit portion of a 64-bit >> build. We need to be careful to only build the table for zones that >> have a corresponding gfp_t flag. GFP_ZONES_SHIFT is introduced for this >> purpose. This patch does not attempt to solve the problem of adding a >> new zone that also has a corresponding GFP_ flag. >> >> Vlastimil points out that ZONE_DEVICE, by depending on x86_64 and >> SPARSEMEM_VMEMMAP implies that SECTIONS_WIDTH is zero. In other words > > ^ by default > > Because CONFIG_SPARSEMEM_VMEMMAP can still be disabled by the user. > >> even though ZONE_DEVICE does not fit in GFP_ZONE_TABLE it is free to >> consume another bit in page->flags (expand ZONES_WIDTH) with room to >> spare. > > So it's still possible to configure the x86_64 kernel such that you get > "#warning Unfortunate NUMA and NUMA Balancing config". But it requires > some effort to override the defaults, and it's not breaking build or > runtime. BTW I was able to get that warning even with your previous > patch that limited NODES_WIDTH, so that wasn't a solution for this > anyway. This patch is simpler and better. All this suggests that ZONE_DEVICE depend on SPARSEMEM_VMEMMAP. I'll fix that up. >> Link: https://bugzilla.kernel.org/show_bug.cgi?id=110931 >> Fixes: 033fbae988fc ("mm: ZONE_DEVICE for "device memory"") >> Cc: Mel Gorman <mgorman@xxxxxxx> >> Cc: Rik van Riel <riel@xxxxxxxxxx> >> Cc: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx> >> Cc: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx> >> Cc: Sudip Mukherjee <sudipm.mukherjee@xxxxxxxxx> >> Reported-by: Mark <markk@xxxxxxxxxxx> >> Reported-by: Vlastimil Babka <vbabka@xxxxxxx> >> Signed-off-by: Dan Williams <dan.j.williams@xxxxxxxxx> > > Acked-by: Vlastimil Babka <vbabka@xxxxxxx> 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>