Quoting Chris Wilson (2018-10-31 09:41:55) > Quoting Kuo-Hsin Yang (2018-10-31 08:19:45) > > The i915 driver uses shmemfs to allocate backing storage for gem > > objects. These shmemfs pages can be pinned (increased ref count) by > > shmem_read_mapping_page_gfp(). When a lot of pages are pinned, vmscan > > wastes a lot of time scanning these pinned pages. In some extreme case, > > all pages in the inactive anon lru are pinned, and only the inactive > > anon lru is scanned due to inactive_ratio, the system cannot swap and > > invokes the oom-killer. Mark these pinned pages as unevictable to speed > > up vmscan. > > > > Add check_move_lru_page() to move page to appropriate lru list. > > > > This patch was inspired by Chris Wilson's change [1]. > > > > [1]: https://patchwork.kernel.org/patch/9768741/ > > > > Cc: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx> > > Cc: Michal Hocko <mhocko@xxxxxxxx> > > Cc: Joonas Lahtinen <joonas.lahtinen@xxxxxxxxxxxxxxx> > > Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx> > > Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> > > Cc: Dave Hansen <dave.hansen@xxxxxxxxx> > > Signed-off-by: Kuo-Hsin Yang <vovoy@xxxxxxxxxxxx> > > --- > > The previous mapping_set_unevictable patch is worse on gem_syslatency > > because it defers to vmscan to move these pages to the unevictable list > > and the test measures latency to allocate 2MiB pages. This performance > > impact can be solved by explicit moving pages to the unevictable list in > > the i915 function. > > > > Chris, can you help to run the "igt/benchmarks/gem_syslatency -t 120 -b -m" > > test with this patch on your testing machine? I tried to run the test on > > a Celeron N4000, 4GB Ram machine. The mean value with this patch is > > similar to that with the mlock patch. > > Will do. As you are confident, I'll try a few different machines. :) I had one anomalous result with Ivybridge, but 3/4 different machines confirm this is effective. I normalized the latency results from each such that 0 is the baseline median latency (no i915 activity) and 1 is the median latency with i915 running drm-tip. N Min Max Median Avg Stddev ivb 120 0.701641 2.79209 1.24469 1.3333911 0.40871825 byt 120 -0.108194 0.0777012 0.0485302 0.01343581 0.061524734 bxt 120 -0.262057 6.27002 0.0801667 0.15963388 0.63528121 kbl 120 -0.0891262 1.22326 -0.0245336 0.041492506 0.14929689 Just need to go back and check on ivb, perhaps running on a few older chipsets as well. But the evidence so far indicates that this eliminates the impact of i915 activity on the performance of shrink_page_list, reducing the amount of crippling stalls under mempressure and often preventing them. -Chris
