The quilt patch titled Subject: mm/hugetlb: fix hugetlb_pmd_shared() has been removed from the -mm tree. Its filename was mm-hugetlb-fix-hugetlb_pmd_shared.patch
This patch was dropped because it was merged into the mm-stable branch of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
------------------------------------------------------ From: "David Hildenbrand (Red Hat)" david@kernel.org Subject: mm/hugetlb: fix hugetlb_pmd_shared() Date: Fri, 5 Dec 2025 22:35:55 +0100
Patch series "mm/hugetlb: fixes for PMD table sharing (incl. using mmu_gather)".
One functional fix, one performance regression fix, and two related comment fixes.
I cleaned up my prototype I recently shared [1] for the performance fix, deferring most of the cleanups I had in the prototype to a later point. While doing that I identified the other things.
The goal of this patch set is to be backported to stable trees "fairly" easily. At least patch #1 and #4.
Patch #1 fixes hugetlb_pmd_shared() not detecting any sharing Patch #2 + #3 are simple comment fixes that patch #4 interacts with. Patch #4 is a fix for the reported performance regression due to excessive IPI broadcasts during fork()+exit().
The last patch is all about TLB flushes, IPIs and mmu_gather. Read: complicated
I added as much comments + description that I possibly could, and I am hoping for review from Jann.
There are plenty of cleanups in the future to be had + one reasonable optimization on x86. But that's all out of scope for this series.
This patch (of 4):
We switched from (wrongly) using the page count to an independent shared count. Now, shared page tables have a refcount of 1 (excluding speculative references) and instead use ptdesc->pt_share_count to identify sharing.
We didn't convert hugetlb_pmd_shared(), so right now, we would never detect a shared PMD table as such, because sharing/unsharing no longer touches the refcount of a PMD table.
Page migration, like mbind() or migrate_pages() would allow for migrating folios mapped into such shared PMD tables, even though the folios are not exclusive. In smaps we would account them as "private" although they are "shared", and we would be wrongly setting the PM_MMAP_EXCLUSIVE in the pagemap interface.
Fix it by properly using ptdesc_pmd_is_shared() in hugetlb_pmd_shared().
Link: https://lkml.kernel.org/r/20251205213558.2980480-1-david@kernel.org Link: https://lkml.kernel.org/r/20251205213558.2980480-2-david@kernel.org Link: https://lore.kernel.org/all/8cab934d-4a56-44aa-b641-bfd7e23bd673@kernel.org/ [1] Fixes: 59d9094df3d7 ("mm: hugetlb: independent PMD page table shared count") Signed-off-by: David Hildenbrand (Red Hat) david@kernel.org Tested-by: Laurence Oberman loberman@redhat.com Reviewed-by: Rik van Riel riel@surriel.com Reviewed-by: Lance Yang lance.yang@linux.dev Cc: Liu Shixin liushixin2@huawei.com Cc: "Aneesh Kumar K.V" aneesh.kumar@kernel.org Cc: Arnd Bergmann arnd@arndb.de Cc: Jann Horn jannh@google.com Cc: Liam Howlett liam.howlett@oracle.com Cc: Lorenzo Stoakes lorenzo.stoakes@oracle.com Cc: Muchun Song muchun.song@linux.dev Cc: Nadav Amit nadav.amit@gmail.com Cc: Nicholas Piggin npiggin@gmail.com Cc: Oscar Salvador osalvador@suse.de Cc: Peter Zijlstra peterz@infradead.org Cc: Prakash Sangappa prakash.sangappa@oracle.com Cc: Vlastimil Babka vbabka@suse.cz Cc: Will Deacon will@kernel.org Cc: Uschakow, Stanislav" suschako@amazon.de Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org ---
include/linux/hugetlb.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
--- a/include/linux/hugetlb.h~mm-hugetlb-fix-hugetlb_pmd_shared +++ a/include/linux/hugetlb.h @@ -1326,7 +1326,7 @@ static inline __init void hugetlb_cma_re #ifdef CONFIG_HUGETLB_PMD_PAGE_TABLE_SHARING static inline bool hugetlb_pmd_shared(pte_t *pte) { - return page_count(virt_to_page(pte)) > 1; + return ptdesc_pmd_is_shared(virt_to_ptdesc(pte)); } #else static inline bool hugetlb_pmd_shared(pte_t *pte) _
Patches currently in -mm which might be from david@kernel.org are