On Thu 18-10-18 14:10:08, Wei Yang wrote: > On Thu, Oct 18, 2018 at 03:15:04PM +0200, Michal Hocko wrote: > >On Thu 18-10-18 21:04:29, Wei Yang wrote: > >> This is not necessary to save the pfn to page->private. > >> > >> The pfn could be retrieved by page_to_pfn() directly. > > > >Yes it can, but a cursory look at the commit which has introduced this > >suggests that this is a micro-optimization. Mel would know more of > >course. There are some memory models where page_to_pfn is close to free. > > > >If that is the case I am not really sure it is measurable or worth it. > >In any case any change to this code should have a proper justification. > >In other words, is this change really needed? Does it help in any > >aspect? Possibly readability? The only thing I can guess from this > >changelog is that you read the code and stumble over this. If that is > >the case I would recommend asking author for the motivation and > >potentially add a comment to explain it better rather than shoot a patch > >rightaway. > > > > Your are right. I am really willing to understand why we want to use > this mechanisum. I am happy to hear that. > So the correct procedure is to send a mail to the mail list to query the > reason? It is certainly better to ask a question than send a patch without a proper justification. I would also encourage to use git blame to see which patch has introduced the specific piece of code. Many times it helps to understand the motivation. I would also encourage to go back to the mailing list archives and the associate discussion to the specific patch. In many cases there is Link: tag which can help you to find the respective discussion. Thanks! -- Michal Hocko SUSE Labs
