> On Tue, Nov 23, 2010 at 5:01 PM, KOSAKI Motohiro > <kosaki.motohiro@xxxxxxxxxxxxxx> 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. > > > > I doubt rsync need to call fdatasync. Why? > > > > If rsync continue to do following loop, some POSIX_FADV_DONTNEED > > may not drop some dirty pages. But they can be dropped at next loop's > > POSIX_FADV_DONTNEED. Then, It doesn't make serious issue. > > > > 1) read > > 2) write > > 3) POSIX_FADV_DONTNEED > > 4) goto 1 > > fadvise need pair (offset and len). > if the pair in next turn is different with one's previous turn, it > couldn't be dropped. invalidate_mapping_pages() are using pagevec_lookup() and pagevec_lookup() are using radix tree lookup. Then, Even if rsync always use [0, inf) pair, I don't think it makes much slowdown. -- 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>