Messages in this thread | | | Subject | Re: [PATCH v2] mm: exclude ZONE_DEVICE from GFP_ZONE_TABLE | From | Vlastimil Babka <> | Date | Fri, 4 Mar 2016 15:11:50 +0100 |
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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.
> Link: https://bugzilla.kernel.org/show_bug.cgi?id=110931 > Fixes: 033fbae988fc ("mm: ZONE_DEVICE for "device memory"") > Cc: Mel Gorman <mgorman@suse.de> > Cc: Rik van Riel <riel@redhat.com> > Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com> > Cc: Dave Hansen <dave.hansen@linux.intel.com> > Cc: Sudip Mukherjee <sudipm.mukherjee@gmail.com> > Reported-by: Mark <markk@clara.co.uk> > Reported-by: Vlastimil Babka <vbabka@suse.cz> > Signed-off-by: Dan Williams <dan.j.williams@intel.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
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