On 1/18/19 6:51 PM, Mel Gorman wrote: > The migration scanner is a linear scan of a zone with a potentiall large > search space. Furthermore, many pageblocks are unusable such as those > filled with reserved pages or partially filled with pages that cannot > migrate. These still get scanned in the common case of allocating a THP > and the cost accumulates. > > The patch uses a partial search of the free lists to locate a migration > source candidate that is marked as MOVABLE when allocating a THP. It > prefers picking a block with a larger number of free pages already on > the basis that there are fewer pages to migrate to free the entire block. > The lowest PFN found during searches is tracked as the basis of the start > for the linear search after the first search of the free list fails. > After the search, the free list is shuffled so that the next search will > not encounter the same page. If the search fails then the subsequent > searches will be shorter and the linear scanner is used. > > If this search fails, or if the request is for a small or > unmovable/reclaimable allocation then the linear scanner is still used. It > is somewhat pointless to use the list search in those cases. Small free > pages must be used for the search and there is no guarantee that movable > pages are located within that block that are contiguous. > > 5.0.0-rc1 5.0.0-rc1 > noboost-v3r10 findmig-v3r15 > Amean fault-both-3 3771.41 ( 0.00%) 3390.40 ( 10.10%) > Amean fault-both-5 5409.05 ( 0.00%) 5082.28 ( 6.04%) > Amean fault-both-7 7040.74 ( 0.00%) 7012.51 ( 0.40%) > Amean fault-both-12 11887.35 ( 0.00%) 11346.63 ( 4.55%) > Amean fault-both-18 16718.19 ( 0.00%) 15324.19 ( 8.34%) > Amean fault-both-24 21157.19 ( 0.00%) 16088.50 * 23.96%* > Amean fault-both-30 21175.92 ( 0.00%) 18723.42 * 11.58%* > Amean fault-both-32 21339.03 ( 0.00%) 18612.01 * 12.78%* > > 5.0.0-rc1 5.0.0-rc1 > noboost-v3r10 findmig-v3r15 > Percentage huge-3 86.50 ( 0.00%) 89.83 ( 3.85%) > Percentage huge-5 92.52 ( 0.00%) 91.96 ( -0.61%) > Percentage huge-7 92.44 ( 0.00%) 92.85 ( 0.44%) > Percentage huge-12 92.98 ( 0.00%) 92.74 ( -0.25%) > Percentage huge-18 91.70 ( 0.00%) 91.71 ( 0.02%) > Percentage huge-24 91.59 ( 0.00%) 92.13 ( 0.60%) > Percentage huge-30 90.14 ( 0.00%) 93.79 ( 4.04%) > Percentage huge-32 90.03 ( 0.00%) 91.27 ( 1.37%) > > This shows an improvement in allocation latencies with similar allocation > success rates. While not presented, there was a 31% reduction in migration > scanning and a 8% reduction on system CPU usage. A 2-socket machine showed > similar benefits. > > [[email protected]: Migrate block that was found-fast, some optimisations] > Signed-off-by: Mel Gorman <[email protected]>
With the followup fix, Acked-by: Vlastimil Babka <[email protected]>
