On Fri, Sep 02, 2011 at 01:45:27AM +0200, Andi Kleen wrote: > On Thu, Sep 01, 2011 at 04:28:08PM -0700, Andrew Morton wrote: > > On Thu, 1 Sep 2011 17:24:17 +0200 > > Andrea Arcangeli <aarcange@xxxxxxxxxx> wrote: > > > > > Ideally direct-io should stop calling get_page() on pages > > > returned by get_user_pages(). > > > > Yeah. get_user_pages() is sufficient. Ideally we should be able to > > undo the get_user_pages() get_page() from within the IO completion > > interrupt and we're done. > > > > Cc Andi, who is our resident dio tweaker ;) > > Noted, I'll put it on my list. Thanks Andi! > Should not be too difficult from a quick look, just the convoluted > nature of direct-io.c requires a lot of double checking. I also had a look but it wasn't trivial, I'm not even sure why direct-io.c has to be convoluted. If we could optimize that, we would stay within get_page_foll() which won't need to take the compound_lock even for tail pages. (compound_lock can't be avoided for put_page on tail pages because it runs long after we release any VM lock) Calling get_page/put_pages more times than necessary is never ideal, I imagine the biggest cost is the atomic_inc on the head page that brings in the cacheline of the head page exclusive, the compound_lock in the second get_page shouldn't have a measurable effect, so I think from a practical prospective it's not more worthwhile to optimize that now, than it already was before. > Cc Andi, who is our resident dio tweaker ;) Thanks :) -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>