On 11/14/24 10:36, Ryan Roberts wrote: > On 14/11/2024 08:23, Vlastimil Babka wrote: >> On 10/14/24 12:58, Ryan Roberts wrote: >>> "struct page_frag_cache" has some optimizations that depend on page >>> size. Let's refactor it a bit so that those optimizations can be >>> determined at run-time for the case where page size is a boot-time >>> parameter. For compile-time page size, the compiler should dead code >>> strip and the result is very similar to before. >>> >>> One wrinkle is that we don't know if we need the size member until >>> runtime. So remove the ifdeffery and always define offset as u32 (needed >>> if PAGE_SIZE is >= 64K) and size as u16 (only used when PAGE_SIZE <= >>> 32K). We move the members around a bit so that the overall size of the >>> struct remains the same; 24 bytes for 64-bit and 16 bytes on 32 bit. >>> >>> Signed-off-by: Ryan Roberts <ryan.roberts@xxxxxxx> >> >> Looks ok, but ideally the PAGE_FRAG_CACHE_MAX_ORDER #define should also be >> replaced by some variable that's populated just once. It can be static local >> to page_alloc.c as nothing else seems to use it. > > I can certainly do that, but wouldn't that be penalizing a compile-time page > size configuration? My current change means that PAGE_FRAG_CACHE_MAX_ORDER still > resolves to a compile-time constant in that situation and the compiler can > eliminate conditional branches it knows will never be taken. Or perhaps you're Ah, I see. > suggesting I conditionally make it a variable if PAGE_SIZE_MIN != PAGE_SIZE_MAX? Given the only place it's being used, it shouldn't be worth it after all. You can add for this patch: Acked-by: Vlastimil Babka <vbabka@xxxxxxx> > Thanks, > Ryan
