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authorMichal Hocko <mhocko@suse.com>2017-09-07 02:20:13 +0300
committerLinus Torvalds <torvalds@linux-foundation.org>2017-09-07 03:27:25 +0300
commitc9bff3eebc09be23fbc868f5e6731666d23cbea3 (patch)
tree3a98933875f125df12e7fa44279bea2e7067f802 /Documentation/vm
parent5a47074f0279421778f97b1b1e75686696a5f42a (diff)
downloadlinux-c9bff3eebc09be23fbc868f5e6731666d23cbea3.tar.xz
mm, page_alloc: rip out ZONELIST_ORDER_ZONE
Patch series "cleanup zonelists initialization", v1. This is aimed at cleaning up the zonelists initialization code we have but the primary motivation was bug report [2] which got resolved but the usage of stop_machine is just too ugly to live. Most patches are straightforward but 3 of them need a special consideration. Patch 1 removes zone ordered zonelists completely. I am CCing linux-api because this is a user visible change. As I argue in the patch description I do not think we have a strong usecase for it these days. I have kept sysctl in place and warn into the log if somebody tries to configure zone lists ordering. If somebody has a real usecase for it we can revert this patch but I do not expect anybody will actually notice runtime differences. This patch is not strictly needed for the rest but it made patch 6 easier to implement. Patch 7 removes stop_machine from build_all_zonelists without adding any special synchronization between iterators and updater which I _believe_ is acceptable as explained in the changelog. I hope I am not missing anything. Patch 8 then removes zonelists_mutex which is kind of ugly as well and not really needed AFAICS but a care should be taken when double checking my thinking. This patch (of 9): Supporting zone ordered zonelists costs us just a lot of code while the usefulness is arguable if existent at all. Mel has already made node ordering default on 64b systems. 32b systems are still using ZONELIST_ORDER_ZONE because it is considered better to fallback to a different NUMA node rather than consume precious lowmem zones. This argument is, however, weaken by the fact that the memory reclaim has been reworked to be node rather than zone oriented. This means that lowmem requests have to skip over all highmem pages on LRUs already and so zone ordering doesn't save the reclaim time much. So the only advantage of the zone ordering is under a light memory pressure when highmem requests do not ever hit into lowmem zones and the lowmem pressure doesn't need to reclaim. Considering that 32b NUMA systems are rather suboptimal already and it is generally advisable to use 64b kernel on such a HW I believe we should rather care about the code maintainability and just get rid of ZONELIST_ORDER_ZONE altogether. Keep systcl in place and warn if somebody tries to set zone ordering either from kernel command line or the sysctl. [mhocko@suse.com: reading vm.numa_zonelist_order will never terminate] Link: http://lkml.kernel.org/r/20170721143915.14161-2-mhocko@kernel.org Signed-off-by: Michal Hocko <mhocko@suse.com> Acked-by: Mel Gorman <mgorman@suse.de> Acked-by: Vlastimil Babka <vbabka@suse.cz> Cc: Johannes Weiner <hannes@cmpxchg.org> Cc: Joonsoo Kim <js1304@gmail.com> Cc: Shaohua Li <shaohua.li@intel.com> Cc: Toshi Kani <toshi.kani@hpe.com> Cc: Abdul Haleem <abdhalee@linux.vnet.ibm.com> Cc: <linux-api@vger.kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'Documentation/vm')
-rw-r--r--Documentation/vm/numa7
1 files changed, 2 insertions, 5 deletions
diff --git a/Documentation/vm/numa b/Documentation/vm/numa
index a08f71647714..a31b85b9bb88 100644
--- a/Documentation/vm/numa
+++ b/Documentation/vm/numa
@@ -79,11 +79,8 @@ memory, Linux must decide whether to order the zonelists such that allocations
fall back to the same zone type on a different node, or to a different zone
type on the same node. This is an important consideration because some zones,
such as DMA or DMA32, represent relatively scarce resources. Linux chooses
-a default zonelist order based on the sizes of the various zone types relative
-to the total memory of the node and the total memory of the system. The
-default zonelist order may be overridden using the numa_zonelist_order kernel
-boot parameter or sysctl. [see Documentation/admin-guide/kernel-parameters.rst and
-Documentation/sysctl/vm.txt]
+a default Node ordered zonelist. This means it tries to fallback to other zones
+from the same node before using remote nodes which are ordered by NUMA distance.
By default, Linux will attempt to satisfy memory allocation requests from the
node to which the CPU that executes the request is assigned. Specifically,