On Mon, May 30, 2016 at 7:15 PM, Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx> wrote: > On Thu, May 26, 2016 at 02:21:42PM -0700, Andrew Morton wrote: >> On Thu, 5 May 2016 17:57:13 +1000 "Oliver O'Halloran" <oohall@xxxxxxxxx> wrote: >> >> > As a part of memory initialisation the architecture passes an array to >> > free_area_init_nodes() which specifies the max PFN of each memory zone. >> > This array is not necessarily monotonic (due to unused zones) so this >> > array is parsed to build monotonic lists of the min and max PFN for >> > each zone. ZONE_MOVABLE is special cased here as its limits are managed by >> > the mm subsystem rather than the architecture. Unfortunately, this special >> > casing is broken when ZONE_MOVABLE is the not the last zone in the zone >> > list. The core of the issue is: >> > >> > if (i == ZONE_MOVABLE) >> > continue; >> > arch_zone_lowest_possible_pfn[i] = >> > arch_zone_highest_possible_pfn[i-1]; >> > >> > As ZONE_MOVABLE is skipped the lowest_possible_pfn of the next zone >> > will be set to zero. This patch fixes this bug by adding explicitly >> > tracking where the next zone should start rather than relying on the >> > contents arch_zone_highest_possible_pfn[]. >> >> hm, this is all ten year old Mel code. >> > > ZONE_MOVABLE at the time always existed at the end of a node during > initialisation time. It was allowed because the memory was always "stolen" > from the end of the node where it could have the same limitations as > ZONE_HIGHMEM if necessary. It was also safe to assume that zones never > overlapped as zones were about addressing limitations. If ZONE_CMA or > ZONE_DEVICE can overlap with other zones during initialisation time then > there may be a few gremlins hiding in there. Unfortunately I have not > done an audit searching for problems with overlapping zones. I think it's still reasonable to assume there is no overlap in early init. The interface to free_area_init_nodes() ensures that zones are disjoint and as far as I can tell the only way to get an overlapping zone at that point is to hit the bug this patch fixes. ZONE_CMA is only populated when core_initcall()s are processed and ZONE_DEVICE is hotplugged by drivers so it should appear even later. -- 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>