On 04/08/2014 06:34 AM, Mel Gorman wrote: > zone_reclaim_mode causes processes to prefer reclaiming memory from local > node instead of spilling over to other nodes. This made sense initially when > NUMA machines were almost exclusively HPC and the workload was partitioned > into nodes. The NUMA penalties were sufficiently high to justify reclaiming > the memory. On current machines and workloads it is often the case that > zone_reclaim_mode destroys performance but not all users know how to detect > this. Favour the common case and disable it by default. Users that are > sophisticated enough to know they need zone_reclaim_mode will detect it. > > Signed-off-by: Mel Gorman <mgor...@suse.de>
Reviewed-by: Zhang Yanfei <zhangyan...@cn.fujitsu.com> > --- > Documentation/sysctl/vm.txt | 17 +++++++++-------- > mm/page_alloc.c | 2 -- > 2 files changed, 9 insertions(+), 10 deletions(-) > > diff --git a/Documentation/sysctl/vm.txt b/Documentation/sysctl/vm.txt > index d614a9b..ff5da70 100644 > --- a/Documentation/sysctl/vm.txt > +++ b/Documentation/sysctl/vm.txt > @@ -751,16 +751,17 @@ This is value ORed together of > 2 = Zone reclaim writes dirty pages out > 4 = Zone reclaim swaps pages > > -zone_reclaim_mode is set during bootup to 1 if it is determined that pages > -from remote zones will cause a measurable performance reduction. The > -page allocator will then reclaim easily reusable pages (those page > -cache pages that are currently not used) before allocating off node pages. > - > -It may be beneficial to switch off zone reclaim if the system is > -used for a file server and all of memory should be used for caching files > -from disk. In that case the caching effect is more important than > +zone_reclaim_mode is disabled by default. For file servers or workloads > +that benefit from having their data cached, zone_reclaim_mode should be > +left disabled as the caching effect is likely to be more important than > data locality. > > +zone_reclaim may be enabled if it's known that the workload is partitioned > +such that each partition fits within a NUMA node and that accessing remote > +memory would cause a measurable performance reduction. The page allocator > +will then reclaim easily reusable pages (those page cache pages that are > +currently not used) before allocating off node pages. > + > Allowing zone reclaim to write out pages stops processes that are > writing large amounts of data from dirtying pages on other nodes. Zone > reclaim will write out dirty pages if a zone fills up and so effectively > diff --git a/mm/page_alloc.c b/mm/page_alloc.c > index 3bac76a..a256f85 100644 > --- a/mm/page_alloc.c > +++ b/mm/page_alloc.c > @@ -1873,8 +1873,6 @@ static void __paginginit init_zone_allows_reclaim(int > nid) > for_each_online_node(i) > if (node_distance(nid, i) <= RECLAIM_DISTANCE) > node_set(i, NODE_DATA(nid)->reclaim_nodes); > - else > - zone_reclaim_mode = 1; > } > > #else /* CONFIG_NUMA */ > -- Thanks. Zhang Yanfei -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
