drm/radeon spamming alloc_contig_range: [xxx, yyy) PFNs busy busy

[Robin H. Johnson]

Somewhere in the Radeon/DRM codebase, CMA page allocation has either
regressed in the timeline of 4.5->4.9, and/or the drm/radeon code is
doing something different with pages.

Given that I haven't seen ANY other reports of this, I'm inclined to
believe the problem is drm/radeon specific (if I don't start X, I can't
reproduce the problem).

The rate of the problem starts slow, and also is relatively low on an idle
system (my screens blank at night, no xscreensaver running), but it still ramps
up over time (to the point of generating 2.5GB/hour of "(timestamp)
alloc_contig_range: [83e4d9, 83e4da) PFNs busy"), with various addresses (~100
unique ranges for a day).

My X workload is ~50 chrome tabs and ~20 terminals (over 3x 24" monitors w/ 9
virtual desktops per monitor).

I added a stack trace & rate limit to alloc_contig_range's PFNs busy message
(patch in previous email on LKML/-MM lists); and they point to radeon.

alloc_contig_range: [83f2a3, 83f2a4) PFNs busy
CPU: 3 PID: 8518 Comm: X Not tainted 4.9.0-rc7-00024-g6ad4037e18ec #27
Hardware name: System manufacturer System Product Name/P8Z68 DELUXE, BIOS 0501 05/09/2011
 ffffad50c3d7f730 ffffffffb236c873 000000000083f2a3 000000000083f2a4
 ffffad50c3d7f810 ffffffffb2183b38 ffff999dff4d8040 0000000020fca8c0
 000000000083f400 000000000083f000 000000000083f2a3 0000000000000004
Call Trace:
 [<ffffffffb236c873>] dump_stack+0x85/0xc2
 [<ffffffffb2183b38>] alloc_contig_range+0x368/0x370
 [<ffffffffb2202d37>] cma_alloc+0x127/0x2e0
 [<ffffffffb24c4b28>] dma_alloc_from_contiguous+0x38/0x40
 [<ffffffffb2020b01>] dma_generic_alloc_coherent+0x91/0x1d0
 [<ffffffffb2049b75>] x86_swiotlb_alloc_coherent+0x25/0x50
 [<ffffffffc0ef17da>] ttm_dma_populate+0x48a/0x9a0 [ttm]
 [<ffffffffb21df8d6>] ? __kmalloc+0x1b6/0x250
 [<ffffffffc0f2a3ea>] radeon_ttm_tt_populate+0x22a/0x2d0 [radeon]
 [<ffffffffc0ee80f7>] ? ttm_dma_tt_init+0x67/0xc0 [ttm]
 [<ffffffffc0ee7cc7>] ttm_tt_bind+0x37/0x70 [ttm]
 [<ffffffffc0ee9e58>] ttm_bo_handle_move_mem+0x528/0x5a0 [ttm]
 [<ffffffffb219464a>] ? shmem_alloc_inode+0x1a/0x30
 [<ffffffffc0eead24>] ttm_bo_validate+0x114/0x130 [ttm]
 [<ffffffffb269346e>] ? _raw_write_unlock+0xe/0x10
 [<ffffffffc0eeb05d>] ttm_bo_init+0x31d/0x3f0 [ttm]
 [<ffffffffc0f2b7ab>] radeon_bo_create+0x19b/0x260 [radeon]
 [<ffffffffc0f2b2e0>] ? radeon_update_memory_usage.isra.0+0x50/0x50 [radeon]
 [<ffffffffc0f3e29d>] radeon_gem_object_create+0xad/0x180 [radeon]
 [<ffffffffc0f3e6ff>] radeon_gem_create_ioctl+0x5f/0xf0 [radeon]
 [<ffffffffc0e3a9eb>] drm_ioctl+0x21b/0x4d0 [drm]
 [<ffffffffc0f3e6a0>] ? radeon_gem_pwrite_ioctl+0x30/0x30 [radeon]
 [<ffffffffc0f0d04c>] radeon_drm_ioctl+0x4c/0x80 [radeon]
 [<ffffffffb221bae2>] do_vfs_ioctl+0x92/0x5c0
 [<ffffffffb221c089>] SyS_ioctl+0x79/0x90
 [<ffffffffb2002bf3>] do_syscall_64+0x73/0x190
 [<ffffffffb26936c8>] entry_SYSCALL64_slow_path+0x25/0x25

The Radeon card in my case is a VisionTek HD 7750 Eyefinity 6, which is
reported as:

01:00.0 VGA compatible controller: Advanced Micro Devices, Inc. [AMD/ATI] Cape Verde PRO [Radeon HD 7750/8740 / R7 250E] (prog-if 00 [VGA controller])
	Subsystem: VISIONTEK Cape Verde PRO [Radeon HD 7750/8740 / R7 250E]
	Flags: bus master, fast devsel, latency 0, IRQ 58
	Memory at c0000000 (64-bit, prefetchable) [size=256M]
	Memory at fbe00000 (64-bit, non-prefetchable) [size=256K]
	I/O ports at e000 [size=256]
	Expansion ROM at 000c0000 [disabled] [size=128K]
	Capabilities: [48] Vendor Specific Information: Len=08 <?>
	Capabilities: [50] Power Management version 3
	Capabilities: [58] Express Legacy Endpoint, MSI 00
	Capabilities: [a0] MSI: Enable+ Count=1/1 Maskable- 64bit+
	Capabilities: [100] Vendor Specific Information: ID=0001 Rev=1 Len=010 <?>
	Capabilities: [150] Advanced Error Reporting
	Kernel driver in use: radeon
	Kernel modules: radeon, amdgpu

-- 
Robin Hugh Johnson
E-Mail     : robbat2 at orbis-terrarum.net
Home Page  : http://www.orbis-terrarum.net/?l=people.robbat2
ICQ#       : 30269588 or 41961639
GnuPG FP   : 11ACBA4F 4778E3F6 E4EDF38E B27B944E 34884E85
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