[Intel-gfx] [PATCH] drm/i915: Do not invalidate obj->pages under mempressure

[shuang.he at intel.com]

Tested-By: PRC QA PRTS (Patch Regression Test System Contact: shuang.he at intel.com)
Task id: 5733
-------------------------------------Summary-------------------------------------
Platform          Delta          drm-intel-nightly          Series Applied
PNV                                  282/283              282/283
ILK              +3-1              308/319              310/319
SNB              +1-3              340/346              338/346
IVB                 -1              378/384              377/384
BYT                                  296/296              296/296
HSW              +2                 421/428              423/428
BDW                                  318/333              318/333
-------------------------------------Detailed-------------------------------------
Platform  Test                                drm-intel-nightly          Series Applied
 ILK  igt_gem_unfence_active_buffers      DMESG_WARN(1, M37)PASS(1, M37)      DMESG_WARN(1, M37)
 ILK  igt_kms_flip_busy-flip-interruptible      TIMEOUT(2, M37)PASS(1, M37)      PASS(1, M37)
*ILK  igt_kms_flip_flip-vs-panning      TIMEOUT(2, M37)      PASS(1, M37)
*ILK  igt_kms_flip_plain-flip-ts-check-interruptible      TIMEOUT(1, M37)      PASS(1, M37)
*SNB  igt_kms_flip_dpms-vs-vblank-race      PASS(4, M22)      DMESG_WARN(1, M22)
 SNB  igt_kms_flip_dpms-vs-vblank-race-interruptible      DMESG_WARN(3, M22)PASS(2, M22)      DMESG_WARN(1, M22)
 SNB  igt_kms_flip_modeset-vs-vblank-race-interruptible      DMESG_WARN(1, M22)PASS(2, M22)      DMESG_WARN(1, M22)
 SNB  igt_kms_pipe_crc_basic_read-crc-pipe-A      DMESG_WARN(1, M22)PASS(6, M22)      PASS(1, M22)
 IVB  igt_gem_pwrite_pread_snooped-copy-performance      DMESG_WARN(1, M34)PASS(3, M34)      DMESG_WARN(1, M34)
 HSW  igt_gem_storedw_loop_blt      DMESG_WARN(2, M20)PASS(3, M20)      PASS(1, M20)
 HSW  igt_gem_storedw_loop_vebox      DMESG_WARN(2, M20)PASS(2, M20)      PASS(1, M20)
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