On Wed, May 12, 2021 at 10:55:22AM +0200, Oscar Salvador wrote:
> On Wed, May 12, 2021 at 12:10:16AM +0900, Naoya Horiguchi wrote:
> > From: Naoya Horiguchi <naoya.horiguchi@xxxxxxx>
> >
> > Now __get_hwpoison_page() could return -EBUSY in a race condition,
> > so it's helpful to handle it by retrying. We already have retry
> > logic, so make get_hwpoison_page() call get_any_page() when called
> > from memory_failure().
>
> As I stated in your previous patch, I think you should start returning -EBUSY
> from this patch onwards.
>
> > static int get_any_page(struct page *p, unsigned long flags)
> > {
> > int ret = 0, pass = 0;
> > @@ -1152,50 +1136,76 @@ static int get_any_page(struct page *p, unsigned long flags)
> > count_increased = true;
> >
> > try_again:
> > - if (!count_increased && !__get_hwpoison_page(p)) {
> > - if (page_count(p)) {
> > - /* We raced with an allocation, retry. */
> > - if (pass++ < 3)
> > - goto try_again;
> > - ret = -EBUSY;
> > - } else if (!PageHuge(p) && !is_free_buddy_page(p)) {
> > - /* We raced with put_page, retry. */
> > - if (pass++ < 3)
> > - goto try_again;
> > - ret = -EIO;
> > + if (!count_increased) {
> > + ret = __get_hwpoison_page(p);
> > + if (!ret) {
> > + if (page_count(p)) {
> > + /* We raced with an allocation, retry. */
> > + if (pass++ < 3)
> > + goto try_again;
> > + ret = -EBUSY;
> > + } else if (!PageHuge(p) && !is_free_buddy_page(p)) {
> > + /* We raced with put_page, retry. */
> > + if (pass++ < 3)
> > + goto try_again;
> > + ret = -EIO;
> > + }
> > + goto out;
> > }
> > + }
>
> I think this can be improved.
>
> We cannot have -EBUSY unless we come from __get_hwpoison_page() (!count_increased),
> so I think a much more natural approach would be to stuff the hunk below in there,
> and then place the other stuff in an else, so something like:
>
> if (!count_increased) {
> ret = __get_hwpoison_page(p);
> if (!ret) {
> if (page_count(p)) {
> /* We raced with an allocation, retry. */
> if (pass++ < 3)
> goto try_again;
> ret = -EBUSY;
> } else if (!PageHuge(p) && !is_free_buddy_page(p)) {
> /* We raced with put_page, retry. */
> if (pass++ < 3)
> goto try_again;
> ret = -EIO;
> }
> goto out;
> } else if (ret == -EBUSY) {
> /* We raced with freeing huge page to buddy, retry. */
> if (pass++ < 3)
> goto try_again;
> }
Moving "if (ret == -EBUSY)" block to here makes sense to me. Thank you.
> } else {
In the original logic, if __get_hwpoison_page() returns 1, we fall into the
"if (PageHuge(p) || PageLRU(p) || __PageMovable(p)" check. I guess that this
"else" seems not necessary?
> /* We do already have a refcount for this page, see if we can
> * handle it.
> */
> if (PageHuge(p) || PageLRU(p) || __PageMovable(p)) {
> ret = 1;
> } else {
> /* A page we cannot handle. Check...
> }
> }
Thanks,
Naoya Horiguchi
