On Tue, 23 Nov 2010 16:40:03 +0900 Minchan Kim <minchan.kim@xxxxxxxxx> wrote: > Hi KOSAKI, > > 2010/11/23 KOSAKI Motohiro <kosaki.motohiro@xxxxxxxxxxxxxx>: > >> By Other approach, app developer uses POSIX_FADV_DONTNEED. > >> But it has a problem. If kernel meets page is writing > >> during invalidate_mapping_pages, it can't work. > >> It is very hard for application programmer to use it. > >> Because they always have to sync data before calling > >> fadivse(..POSIX_FADV_DONTNEED) to make sure the pages could > >> be discardable. At last, they can't use deferred write of kernel > >> so that they could see performance loss. > >> (http://insights.oetiker.ch/linux/fadvise.html) > > > > If rsync use the above url patch, we don't need your patch. > > fdatasync() + POSIX_FADV_DONTNEED should work fine. > > It works well. But it needs always fdatasync before calling fadvise. > For small file, it hurt performance since we can't use the deferred write. fdatasync() is (much) better than nothing, but a userspace application which is carefully managing its IO scheduling should use sync_file_range(SYNC_FILE_RANGE_WRITE) to push data at the disk and should then run fadvise(DONTNEED) against the same data a few seconds later, after the IO has completed. That way, the application won't block against the write I/O at all, unless of course someone else is thrashing the disk as well, etc. If the app is doing a lot of file I/O (eg, rsync) then this shouldn't be too hard to arrange. Although the payback will be pretty small unless the IO-intensive process is also compute-intensive at times. And such applications are a) fairly rare and b) poorly designed: shouldn't be doing heavy IO and heavy compute in the same thread! -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxxx For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom policy in Canada: sign http://dissolvethecrtc.ca/ Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>