Messages in this thread |  | | Date | Mon, 12 Feb 2018 09:34:35 +1000 | From | Nicholas Piggin <> | Subject | Re: [PATCH v4 2/5] powerpc/mm/slice: Enhance for supporting PPC32 |
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On Sun, 11 Feb 2018 21:04:42 +0530 "Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com> wrote:
> On 02/11/2018 07:29 PM, Nicholas Piggin wrote: > > On Sat, 10 Feb 2018 13:54:27 +0100 (CET) > > Christophe Leroy <christophe.leroy@c-s.fr> wrote: > > > >> In preparation for the following patch which will fix an issue on > >> the 8xx by re-using the 'slices', this patch enhances the > >> 'slices' implementation to support 32 bits CPUs. > >> > >> On PPC32, the address space is limited to 4Gbytes, hence only the low > >> slices will be used. > >> > >> This patch moves "slices" functions prototypes from page64.h to slice.h > >> > >> The high slices use bitmaps. As bitmap functions are not prepared to > >> handling bitmaps of size 0, the bitmap_xxx() calls are wrapped into > >> slice_bitmap_xxx() functions which will void on PPC32 > > > > On this last point, I think it would be better to put these with the > > existing slice bitmap functions in slice.c and just have a few #ifdefs > > for SLICE_NUM_HIGH == 0. > > > > We went back and forth with that. IMHO, we should avoid as much #ifdef > as possible across platforms. It helps to understand the platform > restrictions better as we have less and less access to these platforms. > The above change indicates that nohash 32 wants to use the slice code > and they have different restrictions. With that we now know that > book3s64 and nohash 32 are the two different configs using slice code.
I don't think it's the right place to put it. It's not platform dependent so much as it just depends on whether or not you have 0 high slices as a workaround for bitmap API not accepting 0 length.
Another platform that uses the slice code would just have to copy and paste either the nop or the bitmap implementation depending if it has high slices. So I don't think it's the right abstraction. And it implies a bitmap operation but it very specifically only works for struct slice_mask.high_slices bitmap, which is not clear. Better to just work with struct slice_mask.
Some ifdefs inside .c code for small helper functions like this IMO isn't really a big deal -- it's not worse than having it in headers. You just want to avoid ifdef mess when looking at non-trivial logic.
static inline void slice_or_mask(struct slice_mask *dst, struct slice_mask *src) { dst->low_slices |= src->low_slices; #if SLICE_NUM_HIGH > 0 bitmap_or(result, dst->high_slices, src->high_slices, SLICE_NUM_HIGH); #endif }
I think that's pretty fine. If you have a singular hatred for ifdef in .c, then if() works just as well.
Thanks, Nick
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