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On my gbue4k with freshly installed OpenPLi 7.2, I got distortions (artifacts, short stops) when watching a broadcast while it was recorded. Watching a recording while a different broadcast was being recorded didn't show any problems.
For each distortion, I found basically these messages in the log:
gbue4k user.warn kernel: [24938.598392] enigma2: page allocation failure: order:5, mode:0x2040d0
gbue4k user.warn kernel: [24938.604789] CPU: 1 PID: 6503 Comm: enigma2 Tainted: P O 4.1.20-1.9 #1
gbue4k user.warn kernel: [24938.612369] Hardware name: Broadcom STB (Flattened Device Tree)
gbue4k user.warn kernel: [24938.618315] [<c001795c>] (unwind_backtrace) from [<c001323c>] (show_stack+0x10/0x14)
gbue4k user.warn kernel: [24938.626079] [<c001323c>] (show_stack) from [<c065fb8c>] (dump_stack+0x84/0x98)
gbue4k user.warn kernel: [24938.633317] [<c065fb8c>] (dump_stack) from [<c00a8218>] (warn_alloc_failed+0xe4/0x120)
gbue4k user.warn kernel: [24938.641248] [<c00a8218>] (warn_alloc_failed) from [<c00ab158>] (__alloc_pages_nodemask+0x558/0x84c)
gbue4k user.warn kernel: [24938.650308] [<c00ab158>] (__alloc_pages_nodemask) from [<c00ddd34>] (cache_alloc_refill+0x364/0x59c)
gbue4k user.warn kernel: [24938.659454] [<c00ddd34>] (cache_alloc_refill) from [<c00de024>] (__kmalloc_track_caller+0xb8/0xec)
gbue4k user.warn kernel: [24938.668425] [<c00de024>] (__kmalloc_track_caller) from [<c00b9818>] (memdup_user+0x1c/0xa4)
gbue4k user.warn kernel: [24938.676790] [<c00b9818>] (memdup_user) from [<c049ad44>] (dvbdmx_write+0x30/0xb8)
gbue4k user.warn kernel: [24938.684308] [<c049ad44>] (dvbdmx_write) from [<bf63d750>] (dev_dmx_demux_write_hook+0xa0/0xd0 [dvb])
gbue4k user.warn kernel: [24938.693481] [<bf63d750>] (dev_dmx_demux_write_hook [dvb]) from [<bf63da3c>] (dev_dmx_dvr_write_hook+0xfc/0x41c [dvb])
gbue4k user.warn kernel: [24938.704118] [<bf63da3c>] (dev_dmx_dvr_write_hook [dvb]) from [<c00e2fe8>] (__vfs_write+0x1c/0xd8)
gbue4k user.warn kernel: [24938.713002] [<c00e2fe8>] (__vfs_write) from [<c00e37f0>] (vfs_write+0x90/0x170)
gbue4k user.warn kernel: [24938.720319] [<c00e37f0>] (vfs_write) from [<c00e4010>] (SyS_write+0x3c/0x90)
gbue4k user.warn kernel: [24938.727378] [<c00e4010>] (SyS_write) from [<c000ff40>] (ret_fast_syscall+0x0/0x3c)
gbue4k user.warn kernel: [24938.735375] Mem-Info:
gbue4k user.warn kernel: [24938.737755] active_anon:23895 inactive_anon:101 isolated_anon:0
gbue4k user.warn kernel: [24938.737755] active_file:82159 inactive_file:83463 isolated_file:24
gbue4k user.warn kernel: [24938.737755] unevictable:0 dirty:25028 writeback:21977 unstable:0
gbue4k user.warn kernel: [24938.737755] slab_reclaimable:8555 slab_unreclaimable:3144
gbue4k user.warn kernel: [24938.737755] mapped:1347 shmem:3296 pagetables:713 bounce:0
gbue4k user.warn kernel: [24938.737755] free:2881 free_pcp:150 free_cma:65
gbue4k user.warn kernel: [24938.772425] DMA free:8500kB min:2732kB low:3412kB high:4096kB active_anon:34792kB inactive_anon:260kB active_file:158908kB inacti
gbue4k user.warn kernel: [24938.818678] lowmem_reserve[]: 0 0 428 428
gbue4k user.warn kernel: [24938.823584] HighMem free:2888kB min:428kB low:1068kB high:1712kB active_anon:60788kB inactive_anon:144kB active_file:169344kB ina
gbue4k user.warn kernel: [24938.868991] lowmem_reserve[]: 0 0 0 0
gbue4k user.warn kernel: [24938.873261] DMA: 1848*4kB (UEM) 234*8kB (UMR) 34*16kB (UMR) 3*32kB ® 0*64kB 1*128kB ® 0*256kB 0*512kB 0*1024kB 0*2048kB 0*409
gbue4k user.warn kernel: [24938.889174] HighMem: 479*4kB (MRC) 67*8kB ® 10*16kB ® 0*32kB 1*64kB ® 0*128kB 1*256kB ® 0*512kB 0*1024kB 0*2048kB 0*4096k
gbue4k user.warn kernel: [24938.908771] 168589 total pagecache pages
gbue4k user.warn kernel: [24938.913452] 0 pages in swap cache
gbue4k user.warn kernel: [24938.917438] Swap cache stats: add 0, delete 0, find 0/0
gbue4k user.warn kernel: [24938.923274] Free swap = 0kB
gbue4k user.warn kernel: [24938.926618] Total swap = 0kB
gbue4k user.warn kernel: [24938.930039] 524288 pages RAM
gbue4k user.warn kernel: [24938.932952] 400896 pages HighMem/MovableOnly
gbue4k user.warn kernel: [24938.938089] 293632 pages reserved
gbue4k user.warn kernel: [24938.942179] 4096 pages cma reserved
This thread (https://www.opena.tv...-haengt-19.html) discusses the issue at length. It comes down to memory being fragmented in such a way that a buffer of the required size cannot be allocated. The thread ends with settings that didn't fix the problem (neither for me nor in the context of the thread).
However, I found that these "more aggressive" values:
vm.min_free_kbytes = 129072
vm.dirty_ratio = 60
vm.vfs_cache_pressure = 110
fix the problem. I know that the settings may be a bit "exaggerated", I didn't test them individually. It may well be that adjusting only e.g. vm.min_free_kbytes is sufficient.
Maybe this information helps if somebody encounters the same problem.
- Michael
