Re: [PATCHv7 02/14] mm: Add support for unaccepted memory

[Tom Lendacky]

On 8/15/22 16:08, Dionna Amalie Glaze wrote:
> > The unpredictable performance of the application early in boot may be
> > unacceptable and unavoidable. It might take a long time but it could
> > eventually generate bug reports about "unpredictable performance early
> > in boot" that will be hard to track down unless accept_memory is observed
> > using perf at the right time. Even when that does happen, there will need
> > to be an option to turn it off if the unpredictable performance cannot
> > be tolerated. Second, any benchmarking done early in boot is likely to
> > be disrupted making the series a potential bisection magnet that masks a
> > performance bug elsewhere in the merge window.
>
> I'm doing some boot performance tests now before I run some workload
> memory acceptance latency tests.
> Note that this testing is on AMD SEV-SNP, so this patch series on top
> of the AMD guest patches v12, plus a
> patch Brijesh Singh wrote to define __accept_memory for SEV-SNP
> https://github.com/AMDESE/linux/commit/ecae2582666d50ce1e633975d703d2f904183ece

Note that there is a bug in Brijesh's version of the patch and it will 
almost exclusively use the MSR protocol. Please try the version of the 
patch that I recently sent up based on the current unaccepted memory tree 
from Kirill.

https://lore.kernel.org/lkml/cover.1660579062.git.thomas.lendacky@xxxxxxx/

Thanks,
Tom

> I was getting pretty consistent boot times, only going up slightly as
> the memory size increased, but at 256GB, the VM crashes because it
> touches some unaccepted memory without first accepting it. 255GB boots
> fine.
>
> The stack track is in mm/page_alloc.c. I've done a little
> investigation, but I can't account for why there's a hard cutoff of
> correctness at 256GB
>
> [    0.065563] RIP: 0010:memmap_init_range+0x108/0x173
> [    0.066309] Code: 77 16 f6 42 10 02 74 10 48 03 42 08 48 c1 e8 0c
> 48 89 c3 e9 3a ff ff ff 48 89 df 48 c1 e7 06 48 03 3d d9 a2 66 ff 48
> 8d 47 08 <c7> 47 34 01 00 00 00 48 c7 47 38 00 00 00 00 c7 47 30 ff ff
> ff ff
> [    0.069108] RSP: 0000:ffffffffad603dc8 EFLAGS: 00010082 ORIG_RAX:
> 0000000000000404
> [    0.070193] RAX: ffffdba740000048 RBX: 0000000000000001 RCX: 0000000000000000
> [    0.071170] RDX: 0000000000000000 RSI: 0000000000000000 RDI: ffffdba740000040
> [    0.072224] RBP: 0000000000000000 R08: 0000000000001000 R09: 0000000000000000
> [    0.073283] R10: 0000000000000001 R11: ffffffffad645c60 R12: 0000000000000000
> [    0.074304] R13: 00000000000000a0 R14: 0000000000000000 R15: 0000000000000000
> [    0.075285] FS:  0000000000000000(0000) GS:ffffffffadd6c000(0000)
> knlGS:0000000000000000
> [    0.076365] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> [    0.077194] CR2: ffffdba740000074 CR3: 0008001ee3a0c000 CR4: 00000000000606b0
> [    0.078209] Call Trace:
> [    0.078524]  <TASK>
> [    0.078887]  ? free_area_init+0x5c1/0x66c
> [    0.079417]  ? zone_sizes_init+0x52/0x6c
> [    0.079934]  ? setup_arch+0xa55/0xb6d
> [    0.080417]  ? start_kernel+0x64/0x65a
> [    0.080897]  ? secondary_startup_64_no_verify+0xd6/0xdb
> [    0.081620]  </TASK>
>
> > --
> > Mel Gorman
> > SUSE Labs