lkml.org 
[lkml]   [2019]   [Feb]   [8]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
SubjectRe: [PATCH 09/22] mm, compaction: Use free lists to quickly locate a migration source
From
Date
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.
>
> [vbabka@suse.cz: Migrate block that was found-fast, some optimisations]
> Signed-off-by: Mel Gorman <mgorman@techsingularity.net>

With the followup fix,

Acked-by: Vlastimil Babka <Vbabka@suse.cz>

\
 
 \ /
  Last update: 2019-02-08 18:11    [W:0.162 / U:5.476 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site