While using libreoffice draw to edit slides, it became very slow and took
around 5 seconds to get the focus of a object. I found there were a lot of
trace in dmesg, and it probably caused the slowness.

The similar traces repeated several times:

[11455.911766] radeon 0000:01:00.0: swiotlb buffer is full (sz: 2097152 bytes)
[11455.911767] radeon 0000:01:00.0: swiotlb: coherent allocation failed,
size=2097152
[11455.911770] CPU: 6 PID: 2154 Comm: X Not tainted 4.16.1-1-default #1
openSUSE Tumbleweed (unreleased)
[11455.911770] Hardware name: Dell Inc. OptiPlex 9020/0N4YC8, BIOS A12
05/06/2015
[11455.911771] Call Trace:
[11455.911777]  dump_stack+0x85/0xc5
[11455.911780]  swiotlb_alloc_coherent+0x1b6/0x1d0
[11455.911786]  ttm_dma_pool_get_pages+0x1ed/0x5b0 [ttm]
[11455.911790]  ttm_dma_populate+0x25e/0x350 [ttm]
[11455.911792]  ttm_tt_bind+0x2c/0x60 [ttm]
[11455.911795]  ttm_bo_handle_move_mem+0x577/0x5b0 [ttm]
[11455.911798]  ttm_bo_validate+0x100/0x110 [ttm]
[11455.911810]  ? drm_vma_offset_add+0x41/0x60 [drm]
[11455.911816]  ? drm_mode_connector_list_update+0x13e/0x170 [drm]
[11455.911818]  ttm_bo_init_reserved+0x382/0x430 [ttm]
[11455.911821]  ttm_bo_init+0x52/0xc0 [ttm]
[11455.911833]  ? radeon_update_memory_usage.isra.4+0x50/0x50 [radeon]
[11455.911841]  radeon_bo_create+0x180/0x240 [radeon]
[11455.911849]  ? radeon_update_memory_usage.isra.4+0x50/0x50 [radeon]
[11455.911858]  radeon_gem_object_create+0x93/0x180 [radeon]
[11455.911866]  ? radeon_gem_pwrite_ioctl+0x30/0x30 [radeon]
[11455.911874]  radeon_gem_create_ioctl+0x56/0xf0 [radeon]
[11455.911876]  ? unix_stream_recvmsg+0x43/0x50
[11455.911883]  ? radeon_gem_pwrite_ioctl+0x30/0x30 [radeon]
[11455.911888]  drm_ioctl_kernel+0x5b/0xb0 [drm]
[11455.911894]  drm_ioctl+0x2ad/0x350 [drm]
[11455.911901]  ? radeon_gem_pwrite_ioctl+0x30/0x30 [radeon]
[11455.911903]  ? do_iter_write+0xdc/0x190
[11455.911904]  ? vfs_writev+0xaa/0xf0
[11455.911910]  radeon_drm_ioctl+0x49/0x80 [radeon]
[11455.911912]  do_vfs_ioctl+0x90/0x5f0
[11455.911914]  ? __sys_recvmsg+0x5d/0x70
[11455.911916]  ? __fget+0x6e/0xb0
[11455.911917]  SyS_ioctl+0x74/0x80
[11455.911919]  do_syscall_64+0x76/0x140
[11455.911921]  entry_SYSCALL_64_after_hwframe+0x42/0xb7
[11455.911922] RIP: 0033:0x7fcd93f5a967
[11455.911923] RSP: 002b:00007ffc8bcf7528 EFLAGS: 00000246 ORIG_RAX:
0000000000000010
[11455.911924] RAX: ffffffffffffffda RBX: 0000000000000002 RCX:
00007fcd93f5a967
[11455.911925] RDX: 00007ffc8bcf75a0 RSI: 00000000c020645d RDI:
0000000000000010
[11455.911925] RBP: 00007ffc8bcf75a0 R08: 0000000000000002 R09:
0000000000000000
[11455.911926] R10: 0000000000334000 R11: 0000000000000246 R12:
00000000c020645d
[11455.911926] R13: 0000000000000010 R14: 0000561254c21440 R15:
0000000000000002