After having looked at the AUFS stuff some for the Yocto uprev, what I wanted to look at a bit more was the raw patches, like the aufs5-mmap.patch which touches existing core kernel files like mmap.c and fork.c etc.
It is worth noting that the Yocto use case is quite different from the typical RYO user who goes out and sources AUFS for themselves. In the Yocto use case, we have probably 99% of our users who implicitly have AUFS code present but disabled via Kconfig. In the RYO case the code is rarely ever disabled since it was intentionally put there to be used. For those of us who used preempt-rt patches from over a decade ago, we can remember instances where the present-and-enabled case got all the testing and use, and the present-but-disabled case might not even build. That means we should be paying extra attention to ensure the present but disabled case isn't leaving us open to regressions, or any size or performance burdens vs. the unpatched case with no AUFS code present. To that end, I noticed overhead in AUFS that would remain even when disabled that could be relatively easily avoided and I fix that here. Boot testing included AUFS disabled, =y and =m (plus insmod) cases, on the yocto v5.15.30 baseline with the previous AUFS update applied. The two changes made here for the non-MMU case are untested but hopefully "obviously" correct as parallels to the tested MMU instances. Paul. --- Paul Gortmaker (1): aufs: reduce overhead for "code present but disabled" use case. include/linux/mm.h | 15 +++++++++++++++ include/linux/mm_types.h | 4 ++++ mm/Makefile | 3 ++- mm/mmap.c | 12 +++++++++++- 4 files changed, 32 insertions(+), 2 deletions(-) -- 2.17.1
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