linux-kernel - Re: [PATCH v3] mm, drm/i915: mark pinned shmemfs pages as unevictable

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Date:   Wed, 31 Oct 2018 09:41:55 +0000
From:   Chris Wilson <chris@...is-wilson.co.uk>
To:     Kuo-Hsin Yang <vovoy@...omium.org>,
        intel-gfx@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org
Cc:     Kuo-Hsin Yang <vovoy@...omium.org>, Michal Hocko <mhocko@...e.com>,
        Joonas Lahtinen <joonas.lahtinen@...ux.intel.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Dave Hansen <dave.hansen@...el.com>
Subject: Re: [PATCH v3] mm, drm/i915: mark pinned shmemfs pages as unevictable

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@...is-wilson.co.uk>
> Cc: Michal Hocko <mhocko@...e.com>
> Cc: Joonas Lahtinen <joonas.lahtinen@...ux.intel.com>
> Cc: Peter Zijlstra <peterz@...radead.org>
> Cc: Andrew Morton <akpm@...ux-foundation.org>
> Cc: Dave Hansen <dave.hansen@...el.com>
> Signed-off-by: Kuo-Hsin Yang <vovoy@...omium.org>
> ---
> 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. :)
-Chris