On Tue, Jan 2, 2024 at 3:16 PM Suren Baghdasaryan surenb@google.com wrote:
On Tue, Jan 2, 2024 at 8:58 AM Suren Baghdasaryan surenb@google.com wrote:
On Tue, Jan 2, 2024 at 1:00 AM Peter Xu peterx@redhat.com wrote:
On Fri, Dec 29, 2023 at 06:56:07PM -0800, Suren Baghdasaryan wrote:
@@ -1078,9 +1078,14 @@ static int move_pages_pte(struct mm_struct *mm, pmd_t *dst_pmd, pmd_t *src_pmd,
/* at this point we have src_folio locked */ if (folio_test_large(src_folio)) {
/* split_folio() can block */pte_unmap(&orig_src_pte);pte_unmap(&orig_dst_pte);src_pte = dst_pte = NULL; err = split_folio(src_folio); if (err) goto out;goto retry; }Do we also need to clear src_folio and src_folio_pte? If the folio is a thp, I think it means it's pte mapped here. Then after the split we may want to fetch the small folio after the split, not the head one?
I think we need to re-fetch the src_folio only if the src_addr falls into a non-head page. Looking at the __split_huge_page(), the head page is skipped in the last loop, so I think it should stay valid. That said, maybe it's just an implementation detail of the __split_huge_page() and I should not rely on that and refetch anyway?
I'll post a v2 with this fix and re-fetching the folio unconditionally. We also don't need to reset src_folio_pte value because it's used only if src_folio is not NULL.
Posted at https://lore.kernel.org/all/20240102233256.1077959-1-surenb@google.com/
Thanks for catching this, Peter!
-- Peter Xu