On Mon, Dec 12, 2022 at 01:06:16PM -0700, Nathan Chancellor wrote: > On Mon, Dec 12, 2022 at 02:21:57PM -0500, Daniel Jordan wrote: > > On Mon, Dec 12, 2022 at 10:05:02AM -0700, Nathan Chancellor wrote: > > > On Mon, Dec 12, 2022 at 10:07:24PM +0900, Masahiro Yamada wrote: > > > > I am not sure if the compiler should do this level of optimization > > > > because kernel/padata.c does not seem to be a special case. > > > > Perhaps, we might be hit with more cases that need __ref annotation, > > > > which is only required by LTO. > > > > > > That's possible. I did only see this once instance in all my builds but > > > allmodconfig + ThinLTO might not be too interesting of a case, > > > since the sanitizers will be enabled, which makes optimization more > > > difficult. I could try to enable ThinLTO with some distribution > > > configurations to see if there are any more instances that crop up. > > > > Yes, if there were many more instances of this problem it might be worth > > thinking about an LTO-specific solution to fix it closer to the source. > > Ack, I will wire up some build tests to see if this optimization occurs > frequently enough to warrant a wider fix. Turns out this does not appear to happen often. I built several distribution configurations for arm64 and x86_64 with CONFIG_LTO_CLANG_THIN=y and saw no modpost warnings. So I think this is sufficiently odd to keep the fix local to this one instance. I will send a v3 later today. > > > > One note is that, we could discard padata_work_init() > > > > because (1) and (3) are both annotated as __init. > > > > So, another way of fixing is > > > > static __always_inline void padata_work_init(...) > > > > because the compiler would determine padata_work_init() > > > > would be small enough if the caller and callee belonged to > > > > the same section. > > > > > > > > I do not have a strong opinion. > > > > I'm right there with you. :-) > > > > > > Honestly, I do not know what the best approach would be to fix this. > > > > Either approach works, either can include an explanatory comment. > > __ref seems more targeted to the problem at hand. > > Right, I suspect __ref is the right way to go for this particular issue. > I will add a comment regardless. > > > > > If we go with the __ref annotation, I can pick this, but > > > > at least can you add some comments? > > > > > > > > > > > > include/linux/init.h says: > > > > "optimally document why the __ref is needed and why it's OK" > > > > > > > > > > > > I think this is the case that needs some comments > > > > because LTO optimization looks too tricky to me. > > > > > > Sure thing, I will send a v3 either Tuesday or Wednesday with an updated > > > commit message and code comment if we end up going this route. > > > > A nitpick, but as long as you're respinning, if we stay with this > > approach, could you put __ref just before the function name? init.h > > says "The markers follow same syntax rules as __init / __initdata" and > > for those it says "You should add __init immediately before the function > > name" though there are plenty of places in the tree that don't do this. > > Sure thing! > > Cheers, > Nathan >
