On Tue, Nov 23, 2010 at 6:02 PM, KOSAKI Motohiro <kosaki.motohiro@xxxxxxxxxxxxxx> wrote: >> 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. > I mean fdatasync causes slowdown, not fadvise. if you fadvise(don't need) without fdatasync, you could loss the data. -- Kind regards, Minchan Kim -- 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>