Messages in this thread | | | Date | Wed, 15 Jun 2022 13:42:28 +0100 | From | Matthew Wilcox <> | Subject | Re: [PATCH] mm/page_alloc: make calling prep_compound_head more reliable |
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On Wed, Jun 15, 2022 at 03:44:06PM +0800, Miaohe Lin wrote: > > We definitely don't need the unlikely here. > > Could you please give me a more detailed explanation? IIUC, the above if condition > will only meet at a probability of 1/512. So unlikely tells the compiler to do some > optimization around it. Or am I miss something?
Only add unlikely() when the compiler can't figure out for itself that it's unlikely. You should also check the generated code and/or benchmark the results to be sure that it's actually an improvement. Using unlikely() needs to be backed up with more than just a feeling.
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