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Date: Sun, 13 Apr 2008 17:19:53 -0700 From: Andrew Morton <akpm@...ux-foundation.org> To: Benjamin Herrenschmidt <benh@...abs.org> Cc: <linux-kernel@...r.kernel.org>, Paul Mackerras <paulus@...ba.org>, <linuxppc-dev@...abs.org>, <takata@...ux-m32r.org>, <linux-m32r@...linux-m32r.org>, Linux-Arch <linux-arch@...r.kernel.org> Subject: Re: [PATCH 1/2] Add thread_info_cache_init() to all archs On Thu, 10 Apr 2008 13:22:56 +1000 Benjamin Herrenschmidt <benh@...abs.org> wrote: > Some architecture need to maintain a kmem cache for thread info > structures. (next patch adds that to powerpc to fix an alignment > problem). > > There is no good arch callback to use to initialize that cache > that I can find, so this adds a new one and adds an empty macro > for when it's not implemented. > > Signed-off-by: Benjamin Herrenschmidt <benh@...nel.crashing.org> > --- > > So we have the choice here between: > > - the ifdef on the func name that I did, consistent with what > I did before for iomap, which iirc Linus liked > > - add some more ARCH_HAS_* or HAVE_* (yuck) > > - add an empty definition to all archs .h (pain in the neck but I > can do it, though it will be an annoying patch to keep around) > > - do a weak function (will slightly bloat everybody for no good reason) > > So unless there is strong complaints, I'd like to stick to my > current approach. > > include/linux/sched.h | 4 ++++ > init/main.c | 1 + > 2 files changed, 5 insertions(+) > > --- linux-work.orig/init/main.c 2008-04-10 13:11:06.000000000 +1000 > +++ linux-work/init/main.c 2008-04-10 13:11:19.000000000 +1000 > @@ -623,6 +623,7 @@ asmlinkage void __init start_kernel(void > if (efi_enabled) > efi_enter_virtual_mode(); > #endif > + thread_info_cache_init(); > fork_init(num_physpages); > proc_caches_init(); > buffer_init(); > Index: linux-work/include/linux/sched.h > =================================================================== > --- linux-work.orig/include/linux/sched.h 2008-04-10 13:11:44.000000000 +1000 > +++ linux-work/include/linux/sched.h 2008-04-10 13:12:05.000000000 +1000 > @@ -1893,6 +1893,10 @@ static inline unsigned long *end_of_stac > > #endif > > +#ifndef thread_info_cache_init > +#define thread_info_cache_init do { } while(0) > +#endif This trick does cause a bit of a problem: it is undefined which arch header file is to provide the alternative definition of thread_info_cache_init. So we can (and have) ended up in the situation where the override appears in different files on different architectures and various screwups ensue. So I'd suggest that we have a bigfatcomment telling implementors which file the override should be implemented in. And make sure that this arch file is directly included from within sched.h. I have a suspicion that we can still get in a mess if .c files include the per-arch file and don't include sched.h, but I forget where this happened and why it broke stuff. Sigh. A nice, coded-in-C implementation within each and every architecture remains the best implementation, and all the little tricks-to-save-typing have failure modes. otoh, if only one .c file will ever call this function then I think that all problems are solved by a) moving the above ifdeffery into the .c file b) adding a comment explaining which arch file must provide the override c) directly including that file from within the .c file. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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