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[172.10.233.147]) by smtp.gmail.com with ESMTPSA id g10-20020a056902134a00b00b9db62abff3sm1277036ybu.58.2023.05.21.22.23.26 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sun, 21 May 2023 22:23:28 -0700 (PDT) Date: Sun, 21 May 2023 22:23:25 -0700 (PDT) From: Hugh Dickins X-X-Sender: hugh@ripple.attlocal.net To: Andrew Morton cc: Mike Kravetz , Mike Rapoport , "Kirill A. Shutemov" , Matthew Wilcox , David Hildenbrand , Suren Baghdasaryan , Qi Zheng , Yang Shi , Mel Gorman , Peter Xu , Peter Zijlstra , Will Deacon , Yu Zhao , Alistair Popple , Ralph Campbell , Ira Weiny , Steven Price , SeongJae Park , Naoya Horiguchi , Christophe Leroy , Zack Rusin , Jason Gunthorpe , Axel Rasmussen , Anshuman Khandual , Pasha Tatashin , Miaohe Lin , Minchan Kim , Christoph Hellwig , Song Liu , Thomas Hellstrom , linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: [PATCH 26/31] mm/huge_memory: split huge pmd under one pte_offset_map() In-Reply-To: <68a97fbe-5c1e-7ac6-72c-7b9c6290b370@google.com> Message-ID: <3f442a9c-af6d-573d-1ad1-f6f413b1abc9@google.com> References: <68a97fbe-5c1e-7ac6-72c-7b9c6290b370@google.com> MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" __split_huge_zero_page_pmd() use a single pte_offset_map() to sweep the extent: it's already under pmd_lock(), so this is no worse for latency; and since it's supposed to have full control of the just-withdrawn page table, here choose to VM_BUG_ON if it were to fail. And please don't increment haddr by PAGE_SIZE, that should remain huge aligned: declare a separate addr (not a bugfix, but it was deceptive). __split_huge_pmd_locked() likewise (but it had declared a separate addr); and change its BUG_ON(!pte_none) to VM_BUG_ON, for consistency with zero (those deposited page tables are sometimes victims of random corruption). Signed-off-by: Hugh Dickins Reviewed-by: Yang Shi --- mm/huge_memory.c | 28 ++++++++++++++++++---------- 1 file changed, 18 insertions(+), 10 deletions(-) diff --git a/mm/huge_memory.c b/mm/huge_memory.c index d4bd5fa7c823..839c13fa0bbe 100644 --- a/mm/huge_memory.c +++ b/mm/huge_memory.c @@ -2037,6 +2037,8 @@ static void __split_huge_zero_page_pmd(struct vm_area= _struct *vma, struct mm_struct *mm =3D vma->vm_mm; pgtable_t pgtable; pmd_t _pmd, old_pmd; + unsigned long addr; + pte_t *pte; int i; =20 /* @@ -2052,17 +2054,20 @@ static void __split_huge_zero_page_pmd(struct vm_ar= ea_struct *vma, pgtable =3D pgtable_trans_huge_withdraw(mm, pmd); pmd_populate(mm, &_pmd, pgtable); =20 - for (i =3D 0; i < HPAGE_PMD_NR; i++, haddr +=3D PAGE_SIZE) { - pte_t *pte, entry; - entry =3D pfn_pte(my_zero_pfn(haddr), vma->vm_page_prot); + pte =3D pte_offset_map(&_pmd, haddr); + VM_BUG_ON(!pte); + for (i =3D 0, addr =3D haddr; i < HPAGE_PMD_NR; i++, addr +=3D PAGE_SIZE)= { + pte_t entry; + + entry =3D pfn_pte(my_zero_pfn(addr), vma->vm_page_prot); entry =3D pte_mkspecial(entry); if (pmd_uffd_wp(old_pmd)) entry =3D pte_mkuffd_wp(entry); - pte =3D pte_offset_map(&_pmd, haddr); VM_BUG_ON(!pte_none(*pte)); - set_pte_at(mm, haddr, pte, entry); - pte_unmap(pte); + set_pte_at(mm, addr, pte, entry); + pte++; } + pte_unmap(pte - 1); smp_wmb(); /* make pte visible before pmd */ pmd_populate(mm, pmd, pgtable); } @@ -2077,6 +2082,7 @@ static void __split_huge_pmd_locked(struct vm_area_st= ruct *vma, pmd_t *pmd, bool young, write, soft_dirty, pmd_migration =3D false, uffd_wp =3D false; bool anon_exclusive =3D false, dirty =3D false; unsigned long addr; + pte_t *pte; int i; =20 VM_BUG_ON(haddr & ~HPAGE_PMD_MASK); @@ -2205,8 +2211,10 @@ static void __split_huge_pmd_locked(struct vm_area_s= truct *vma, pmd_t *pmd, pgtable =3D pgtable_trans_huge_withdraw(mm, pmd); pmd_populate(mm, &_pmd, pgtable); =20 + pte =3D pte_offset_map(&_pmd, haddr); + VM_BUG_ON(!pte); for (i =3D 0, addr =3D haddr; i < HPAGE_PMD_NR; i++, addr +=3D PAGE_SIZE)= { - pte_t entry, *pte; + pte_t entry; /* * Note that NUMA hinting access restrictions are not * transferred to avoid any possibility of altering @@ -2249,11 +2257,11 @@ static void __split_huge_pmd_locked(struct vm_area_= struct *vma, pmd_t *pmd, entry =3D pte_mkuffd_wp(entry); page_add_anon_rmap(page + i, vma, addr, false); } - pte =3D pte_offset_map(&_pmd, addr); - BUG_ON(!pte_none(*pte)); + VM_BUG_ON(!pte_none(*pte)); set_pte_at(mm, addr, pte, entry); - pte_unmap(pte); + pte++; } + pte_unmap(pte - 1); =20 if (!pmd_migration) page_remove_rmap(page, vma, true); --=20 2.35.3