On Mon, 2 Nov 2015, Andrea Arcangeli wrote: > On Sun, Oct 25, 2015 at 04:18:05PM -0700, Hugh Dickins wrote: > > On Thu, 15 Oct 2015, Andrea Arcangeli wrote: > > > > > get_mergeable_page() can only return NULL (in case of errors) or the > > > pinned mergeable page. It can't return an error different than > > > NULL. This makes it more readable and less confusion in addition to > > > optimizing the check. > > > > > > Signed-off-by: Andrea Arcangeli <aarcange@xxxxxxxxxx> > > > > I share your sentiment, prefer to avoid an unnecessary IS_ERR_OR_NULL. > > And you may be right that it's unnecessary; but that's far from clear > > to me, and you haven't changed the IS_ERR_OR_NULL after follow_page() > > in get_mergeable_page() where it originates, so I wonder if you just > > got confused on this. > > > > Even if you have established that there's currently no way that > > follow_page(vma, addr, FOLL_GET) could return an -errno on a vma > > validated by find_mergeable_vma(), I think we'd still be better off > > to allow for some future -errno there; but I'd be happy for you to > > keep the change below, but also adjust get_mergeable_page() to > > convert an -errno immediately to NULL after follow_page(). > > > > So, I think this is gently Nacked in its present form, > > but a replacement eagerly Acked. > > The "out:" label is followed by page = NULL, so if follow_page returns > an error, get_mergeable_page still cannot return an error. Ah, yes, I missed that, thanks. Acked-by: Hugh Dickins <hughd@xxxxxxxxxx> > > If this wasn't the case, get_mergeable_page would return an > uninitialized pointer if find_mergeable_vma would return NULL. > > I guess the IS_ERR_OR_NULL that I removed, was the direct result of > overlooking the location of the "out:". > > If there was a return after the "out:" the readability would have been > improved, but I haven't touched the code around the "out:". That's the > way it was before. Now I'll add a return in this same patch after the > "out:" before resubmitting without 1/6. I can't very well claim now that it was readable before, can I?-) We'll see; I wouldn't mind if you leave this patch as is. Hugh -- 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/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>