Do you plan to merge this patch? I would like to post my
__GFP_RETRY_MAYFAIL series sometime soon and would like to cover this
one as well.
On Mon 05-06-17 11:35:12, Chris Wilson wrote:
> I tried __GFP_NORETRY in the belief that __GFP_RECLAIM was effective. It
> struggles with handling reclaim via kswapd (through inconsistency within
> throttle_direct_reclaim() and even then the race between multiple
> allocators makes the two step of reclaim then allocate fragile), and as
> our buffers are always dirty (with very few exceptions), we required
> kswapd to perform pageout on them. The only effective means of waiting
> on kswapd is to retry the allocations (i.e. not set __GFP_NORETRY). That
> leaves us with the dilemma of invoking the oomkiller instead of
> propagating the allocation failure back to userspace where it can be
> handled more gracefully (one hopes). In the future we may have
> __GFP_MAYFAIL to allow repeats up until we genuinely run out of memory
> and the oomkiller would have been invoked. Until then, let the oomkiller
> wreck havoc.
>
> v2: Stop playing with side-effects of gfp flags and await __GFP_MAYFAIL
>
> Fixes: 24f8e00a8a2e ("drm/i915: Prefer to report ENOMEM rather than incur the oom for gfx allocations")
> Testcase: igt/gem_tiled_swapping
> Signed-off-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
> Cc: Joonas Lahtinen <joonas.lahtinen@xxxxxxxxxxxxxxx>
> Cc: Daniel Vetter <daniel.vetter@xxxxxxxx>
> Cc: Michal Hocko <mhocko@xxxxxxxx>
> ---
> drivers/gpu/drm/i915/i915_gem.c | 15 ++++++++++++++-
> 1 file changed, 14 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
> index 7286f5dd3e64..845df6067e90 100644
> --- a/drivers/gpu/drm/i915/i915_gem.c
> +++ b/drivers/gpu/drm/i915/i915_gem.c
> @@ -2406,7 +2406,20 @@ i915_gem_object_get_pages_gtt(struct drm_i915_gem_object *obj)
> if (!*s) {
> /* reclaim and warn, but no oom */
> gfp = mapping_gfp_mask(mapping);
> - gfp |= __GFP_NORETRY;
> +
> + /* Our bo are always dirty and so we require
> + * kswapd to reclaim our pages (direct reclaim
> + * performs no swapping on its own). However,
> + * direct reclaim is meant to wait for kswapd
> + * when under pressure, this is broken. As a
> + * result __GFP_RECLAIM is unreliable and fails
> + * to actually reclaim dirty pages -- unless
> + * you try over and over again with
> + * !__GFP_NORETRY. However, we still want to
> + * fail this allocation rather than trigger
> + * the out-of-memory killer and for this we
> + * want the future __GFP_MAYFAIL.
> + */
> }
> } while (1);
>
> --
> 2.11.0
>
--
Michal Hocko
SUSE Labs
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