On Fri 02-08-13 16:47:10, Johannes Weiner wrote: > On Fri, Aug 02, 2013 at 06:27:22PM +0200, Michal Hocko wrote: > > On Fri 02-08-13 11:07:56, Joonsoo Kim wrote: > > > We rarely allocate a page with ALLOC_NO_WATERMARKS and it is used > > > in slow path. For making fast path more faster, add likely macro to > > > help compiler optimization. > > > > The code is different in mmotm tree (see mm: page_alloc: rearrange > > watermark checking in get_page_from_freelist) > > Yes, please rebase this on top. > > > Besides that, make sure you provide numbers which prove your claims > > about performance optimizations. > > Isn't that a bit overkill? We know it's a likely path (we would > deadlock constantly if a sizable portion of allocations were to ignore > the watermarks). Does he have to justify that likely in general makes > sense?
That was more a generic comment. If there is a claim that something would be faster it would be nice to back that claim by some numbers (e.g. smaller hot path). In this particular case, unlikely(alloc_flags & ALLOC_NO_WATERMARKS) doesn't make any change to the generated code with gcc 4.8.1 resp. 4.3.4 I have here. Maybe other versions of gcc would benefit from the hint but changelog didn't tell us. I wouldn't add the anotation if it doesn't make any difference for the resulting code. -- Michal Hocko SUSE Labs -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
