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SubjectRe: [PATCH v3] mm, drm/i915: mark pinned shmemfs pages as unevictable
On Thu, Nov 1, 2018 at 12:42 AM Michal Hocko <mhocko@kernel.org> wrote:
> On Wed 31-10-18 07:40:14, Dave Hansen wrote:
> > Didn't we create the unevictable lists in the first place because
> > scanning alone was observed to be so expensive in some scenarios?
>
> Yes, that is the case. I might just misunderstood the code I thought
> those pages were already on the LRU when unevictable flag was set and
> we would only move these pages to the unevictable list lazy during the
> reclaim. If the flag is set at the time when the page is added to the
> LRU then it should get to the proper LRU list right away. But then I do
> not understand the test results from previous run at all.

"gem_syslatency -t 120 -b -m" allocates a lot of anon pages, it consists of
these looping threads:
* ncpu threads to alloc i915 shmem buffers, these buffers are freed by i915
shrinker.
* ncpu threads to mmap, write, munmap an 2 MiB mapping.
* 1 thread to cat all files to /dev/null

Without the unevictable patch, after rebooting and running
"gem_syslatency -t 120 -b -m", I got these custom vmstat:
pgsteal_kswapd_anon 29261
pgsteal_kswapd_file 1153696
pgsteal_direct_anon 255
pgsteal_direct_file 13050
pgscan_kswapd_anon 14524536
pgscan_kswapd_file 1488683
pgscan_direct_anon 1702448
pgscan_direct_file 25849

And meminfo shows large anon lru size during test.
# cat /proc/meminfo | grep -i "active("
Active(anon): 377760 kB
Inactive(anon): 3195392 kB
Active(file): 19216 kB
Inactive(file): 16044 kB

With this patch, the custom vmstat after test:
pgsteal_kswapd_anon 74962
pgsteal_kswapd_file 903588
pgsteal_direct_anon 4434
pgsteal_direct_file 14969
pgscan_kswapd_anon 2814791
pgscan_kswapd_file 1113676
pgscan_direct_anon 526766
pgscan_direct_file 32432

The anon pgscan count is reduced.

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