My apology for the gobbled message earlier.
On 4/26/2024 12:52 PM, Jane Chu wrote:
On 4/26/2024 12:05 PM, Matthew Wilcox wrote:
[..]
That would be unsafe, the safe way would be if we moved page_folio()
after
the call to __get_hw_poison() in get_any_page() and there would
still be one
remaining user of shake_page() that we can't convert. A safe version
of this
patch would result in a removal of one use of PageHuge() and two
uses of
put_page(), would that be worth submitting?
get_any_page()
if(__get_hwpoison_page())
folio = page_folio() /* folio_try_get() returned 1, safe */
I think we should convert __get_hwpoison_page() to return either the
folio
or an ERR_PTR or NULL. Also, I think we should delete the "cannot catch
tail" part and just loop in __get_hwpoison_page() until we do catch it.
See try_get_folio() in mm/gup.c for inspiration (although you can't use
it exactly because that code knows that the page is mapped into a page
table, so has a refcount).
But that's just an immediate assessment; you might find a reason that
doesn't work.
Besides, in a possible hugetlb demote scenario, it seems to me that we
should retry
get_hwpoison_hugetlb_folio() instead of falling thru to folio_try_get().
static int __get_hwpoison_page(struct page *page, unsigned long flags)
{
struct folio *folio = page_folio(page);
int ret = 0;
bool hugetlb = false;
ret = get_hwpoison_hugetlb_folio(folio, &hugetlb, false);
if (hugetlb) {
/* Make sure hugetlb demotion did not happen from under
us. */
if (folio == page_folio(page))
return ret;
if (ret > 0) { <===== still hugetlb, don't fall
thru, retry
folio_put(folio);
folio = page_folio(page);
}
}
thanks!
-jane
