On Thu, Mar 24, 2016 at 01:32:25AM +0000, Li, Liang Z wrote: >> >> >> > >> >> >> >6. Handling page cache in the guest The memory used for page >> >> >> >cache in the guest will change depends on the workload, if guest >> >> >> >run some block IO intensive work load, there will >> >> >> >> >> >> Would this improvement benefit a lot when guest only has little free >> page? >> >> > >> >> >Yes, the improvement is very obvious. >> >> > >> >> >> >> Good to know this. >> >> >> >> >> In your Performance data Case 2, I think it mimic this kind of case. >> >> >> While the memory consuming task is stopped before migration. If it >> >> >> continues, would we still perform better than before? >> >> > >> >> >Actually, my RFC patch didn't consider the page cache, Roman raised >> >> >this >> >> issue. >> >> >so I add this part in this doc. >> >> > >> >> >Case 2 didn't mimic this kind of scenario, the work load is an >> >> >memory consuming work load, not an block IO intensive work load, so >> >> >there are not many page cache in this case. >> >> > >> >> >If the work load in case 2 continues, as long as it not write all >> >> >the memory it allocates, we still can get benefits. >> >> > >> >> >> >> Sounds I have little knowledge on page cache, and its relationship >> >> between free page and I/O intensive work. >> >> >> >> Here is some personal understanding, I would appreciate if you could >> >> correct me. >> >> >> >> +---------+ >> >> |PageCache| >> >> +---------+ >> >> +---------+---------+---------+---------+ >> >> |Page |Page |Free Page|Page | >> >> +---------+---------+---------+---------+ >> >> >> >> Free Page is a page in the free_list, PageCache is some page cached >> >> in CPU's cache line? >> > >> >No, page cache is quite different with CPU cache line. >> >" In computing, a page cache, sometimes also called disk cache,[2] is a >> >transparent cache for the pages originating from a secondary storage >> device such as a hard disk drive (HDD). >> > The operating system keeps a page cache in otherwise unused portions >> >of the main memory (RAM), resulting in quicker access to the contents >> >of cached pages and overall performance improvements " >> >you can refer to https://en.wikipedia.org/wiki/Page_cache >> >for more details. >> > >> >> My poor knowledge~ Should google it before I imagine the meaning of the >> terminology. >> >> If my understanding is correct, the Page Cache is counted as Free Page, while >> actually we should migrate them instead of filter them. > >No, the Page Cache is not counted as Free Page ... OK, I misunderstand the concept in wiki. The Page Cache is a trade off between Free Page percentage and the I/O performance in guest. > >Liang -- Richard Yang\nHelp you, Help me -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
