Re: [PATCH RFC 0/4] static key support for error injection functions

[David Rientjes]

On Fri, 31 May 2024, Vlastimil Babka wrote:

> Patches 3 and 4 implement the static keys for the two mm fault injection
> sites in slab and page allocators. For a quick demonstration I've run a
> VM and the simple test from [1] that stresses the slab allocator and got
> this time before the series:
> 
> real    0m8.349s
> user    0m0.694s
> sys     0m7.648s
> 
> with perf showing
> 
>    0.61%  nonexistent  [kernel.kallsyms]  [k] should_failslab.constprop.0
>    0.00%  nonexistent  [kernel.kallsyms]  [k] should_fail_alloc_page                                                                                                                                                                                        ▒
> 
> And after the series
> 
> real    0m7.924s
> user    0m0.727s
> sys     0m7.191s
> 
> and the functions gone from perf report.
> 

Impressive results that will no doubt be a win for kernels that enable 
these options.

Both CONFIG_FAILSLAB and CONFIG_FAIL_PAGE_ALLOC go out of their way to 
have no overhead, both in performance and kernel text overhead, when the 
.config options are disabled.

Do we have any insight into the distros or users that enable either of 
these options and are expecting optimal performance?  I would have assumed 
that while CONFIG_FAULT_INJECTION may be enabled that any users who would 
care deeply about this would have disabled both of these debug options.

> There might be other such fault injection callsites in hotpaths of other
> subsystems but I didn't search for them at this point.
> 
> [1] https://lore.kernel.org/all/6d5bb852-8703-4abf-a52b-90816bccbd7f@xxxxxxx/
> [2] https://lore.kernel.org/all/3j5d3p22ssv7xoaghzraa7crcfih3h2qqjlhmjppbp6f42pg2t@kg7qoicog5ye/
> 
> Signed-off-by: Vlastimil Babka <vbabka@xxxxxxx>
> ---
> Vlastimil Babka (4):
>       fault-inject: add support for static keys around fault injection sites
>       error-injection: support static keys around injectable functions
>       mm, slab: add static key for should_failslab()
>       mm, page_alloc: add static key for should_fail_alloc_page()
> 
>  include/asm-generic/error-injection.h | 13 ++++++++++-
>  include/asm-generic/vmlinux.lds.h     |  2 +-
>  include/linux/error-injection.h       |  9 +++++---
>  include/linux/fault-inject.h          |  7 +++++-
>  kernel/fail_function.c                | 22 +++++++++++++++---
>  lib/error-inject.c                    |  6 ++++-
>  lib/fault-inject.c                    | 43 ++++++++++++++++++++++++++++++++++-
>  mm/fail_page_alloc.c                  |  3 ++-
>  mm/failslab.c                         |  2 +-
>  mm/internal.h                         |  2 ++
>  mm/page_alloc.c                       | 11 ++++++---
>  mm/slab.h                             |  3 +++
>  mm/slub.c                             | 10 +++++---
>  13 files changed, 114 insertions(+), 19 deletions(-)
> ---
> base-commit: 1613e604df0cd359cf2a7fbd9be7a0bcfacfabd0
> change-id: 20240530-fault-injection-statickeys-66b7222e91b7
> 
> Best regards,
> -- 
> Vlastimil Babka <vbabka@xxxxxxx>
> 
>