drm/i915: Avoid evicting user fault mappable vma for pread/pwrite
Both pread/pwrite GTT paths provide a fast fallback in case we cannot map the whole object at a time. Currently, we use the fallback for very large objects and for active objects that would require remapping, but we can also add active fault mappable objects to the list that we want to avoid evicting. The rationale is that such fault mappable objects are in active use and to evict requires tearing down the CPU PTE and forcing a page fault on the next access; more costly, and intefers with other processes, than our per-page GTT fallback. Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Link: https://patchwork.freedesktop.org/patch/msgid/20171009084401.29090-6-chris@chris-wilson.co.uk Reviewed-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
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