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When doing compaction, I found the lru_add_drain() is an obvious hotspot
when migrating pages. The distribution of this hotspot is as follows:
- 18.75% compact_zone
- 17.39% migrate_pages
- 13.79% migrate_pages_batch
- 11.66% migrate_folio_move
- 7.02% lru_add_drain
+ 7.02% lru_add_drain_cpu
+ 3.00% move_to_new_folio
1.23% rmap_walk
+ 1.92% migrate_folio_unmap
+ 3.20% migrate_pages_sync
+ 0.90% isolate_migratepages
The lru_add_drain() was added by commit c3096e6782 ("mm/migrate:
__unmap_and_move() push good newpage to LRU") to drain the newpage to LRU
immediately, to help to build up the correct newpage->mlock_count in
remove_migration_ptes() for mlocked pages. However, if there are no
mlocked pages are migrating, then we can avoid this lru drain operation,
especailly for the heavy concurrent scenarios.
So we can record the source pages' mlocked status in
migrate_folio_unmap(), and only drain the lru list when the mlocked status
is set in migrate_folio_move().
In addition, the page was already isolated from lru when migrating, so
checking the mlocked status is stable by folio_test_mlocked() in
migrate_folio_unmap().
After this patch, I can see the hotpot of the lru_add_drain() is gone:
- 9.41% migrate_pages_batch
- 6.15% migrate_folio_move
- 3.64% move_to_new_folio
+ 1.80% migrate_folio_extra
+ 1.70% buffer_migrate_folio
+ 1.41% rmap_walk
+ 0.62% folio_add_lru
+ 3.07% migrate_folio_unmap
Meanwhile, the compaction latency shows some improvements when running
thpscale:
base patched
Amean fault-both-1 1131.22 ( 0.00%) 1112.55 * 1.65%*
Amean fault-both-3 2489.75 ( 0.00%) 2324.15 * 6.65%*
Amean fault-both-5 3257.37 ( 0.00%) 3183.18 * 2.28%*
Amean fault-both-7 4257.99 ( 0.00%) 4079.04 * 4.20%*
Amean fault-both-12 6614.02 ( 0.00%) 6075.60 * 8.14%*
Amean fault-both-18 10607.78 ( 0.00%) 8978.86 * 15.36%*
Amean fault-both-24 14911.65 ( 0.00%) 11619.55 * 22.08%*
Amean fault-both-30 14954.67 ( 0.00%) 14925.66 * 0.19%*
Amean fault-both-32 16654.87 ( 0.00%) 15580.31 * 6.45%*
Link: https://lkml.kernel.org/r/06e9153a7a4850352ec36602df3a3a844de45698.1697859741.git.baolin.wang@linux.alibaba.com
Signed-off-by: Baolin Wang <baolin.wang@linux.alibaba.com>
Reviewed-by: "Huang, Ying" <ying.huang@intel.com>
Reviewed-by: Zi Yan <ziy@nvidia.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Mel Gorman <mgorman@techsingularity.net>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Yin Fengwei <fengwei.yin@intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.