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Sat, 28 Mar 2026 11:49:27 -0700 (PDT) MIME-Version: 1.0 References: In-Reply-To: From: Suren Baghdasaryan Date: Sat, 28 Mar 2026 11:49:17 -0700 X-Gm-Features: AQROBzBdEWDwxPGuda-gZ28S-EX-AfB6_NSRFDtvf06b-OFXIblYAI4TAW9Gjg8 Message-ID: Subject: Re: [PATCH v3 01/13] mm/huge_memory: simplify vma_is_specal_huge() To: "Lorenzo Stoakes (Oracle)" Cc: Andrew Morton , David Hildenbrand , Zi Yan , Baolin Wang , "Liam R . Howlett" , Nico Pache , Ryan Roberts , Dev Jain , Barry Song , Lance Yang , Vlastimil Babka , Mike Rapoport , Michal Hocko , Kiryl Shutsemau , linux-mm@kvack.org, linux-kernel@vger.kernel.org Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Rspam-User: X-Stat-Signature: e6muhwwc37dhffko1cwpqnugjarbc9qg X-Rspamd-Queue-Id: 926B04000D X-Rspamd-Server: rspam09 X-HE-Tag: 1774723769-920099 X-HE-Meta: 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 5pBIZ6Hk zcGnPQiQEFoiIRErLMtGYZJcvtjDDqcQhxpnRK11jmKlCvhbtW7ZrTKMgesVVUnN4dvapEWEJ01fGSm3e7M4JRfBUAYGqYnXRp8rBIXlk/azzmbEoxhUwsbXpUzU704TDQgMSukMoYkCwN+tonm/ciPGG8KJkoVcoH6Rx3GO7S4nNGJjFpFIrdEeInO3kW5dB4YGuUOWYduvZOg6iKJvyZSKvnm87bp4906mzspqYPsew/a/+MiX/vu6mlGd8dmNclbKnS4giYjA8BPFXDIdlrFeIGVN09bd8eDQYTUX5Jpr7sx8= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Fri, Mar 20, 2026 at 11:07=E2=80=AFAM Lorenzo Stoakes (Oracle) wrote: > > This function is confused - it overloads the term 'special' yet again, > checks for DAX but in many cases the code explicitly excludes DAX before > invoking the predicate. > > It also unnecessarily checks for vma->vm_file - this has to be present fo= r > a driver to have set VMA_MIXEDMAP_BIT or VMA_PFNMAP_BIT. > > In fact, a far simpler form of this is to reverse the DAX predicate and > return false if DAX is set. > > This makes sense from the point of view of 'special' as in > vm_normal_page(), as DAX actually does potentially have retrievable > folios. > > Also there's no need to have this in mm.h so move it to huge_memory.c. > > No functional change intended. > > Signed-off-by: Lorenzo Stoakes (Oracle) Reviewed-by: Suren Baghdasaryan > --- > include/linux/huge_mm.h | 4 ++-- > include/linux/mm.h | 16 ---------------- > mm/huge_memory.c | 30 +++++++++++++++++++++++------- > 3 files changed, 25 insertions(+), 25 deletions(-) > > diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h > index 8d801ed378db..af726f0aa30d 100644 > --- a/include/linux/huge_mm.h > +++ b/include/linux/huge_mm.h > @@ -83,7 +83,7 @@ extern struct kobj_attribute thpsize_shmem_enabled_attr= ; > * file is never split and the MAX_PAGECACHE_ORDER limit does not apply = to > * it. Same to PFNMAPs where there's neither page* nor pagecache. > */ > -#define THP_ORDERS_ALL_SPECIAL \ > +#define THP_ORDERS_ALL_SPECIAL_DAX \ > (BIT(PMD_ORDER) | BIT(PUD_ORDER)) > #define THP_ORDERS_ALL_FILE_DEFAULT \ > ((BIT(MAX_PAGECACHE_ORDER + 1) - 1) & ~BIT(0)) > @@ -92,7 +92,7 @@ extern struct kobj_attribute thpsize_shmem_enabled_attr= ; > * Mask of all large folio orders supported for THP. > */ > #define THP_ORDERS_ALL \ > - (THP_ORDERS_ALL_ANON | THP_ORDERS_ALL_SPECIAL | THP_ORDERS_ALL_FI= LE_DEFAULT) > + (THP_ORDERS_ALL_ANON | THP_ORDERS_ALL_SPECIAL_DAX | THP_ORDERS_AL= L_FILE_DEFAULT) > > enum tva_type { > TVA_SMAPS, /* Exposing "THPeligible:" in smaps. */ > diff --git a/include/linux/mm.h b/include/linux/mm.h > index 8aadf115278e..6b07ee99b38b 100644 > --- a/include/linux/mm.h > +++ b/include/linux/mm.h > @@ -5078,22 +5078,6 @@ long copy_folio_from_user(struct folio *dst_folio, > const void __user *usr_src, > bool allow_pagefault); > > -/** > - * vma_is_special_huge - Are transhuge page-table entries considered spe= cial? > - * @vma: Pointer to the struct vm_area_struct to consider > - * > - * Whether transhuge page-table entries are considered "special" followi= ng > - * the definition in vm_normal_page(). > - * > - * Return: true if transhuge page-table entries should be considered spe= cial, > - * false otherwise. > - */ > -static inline bool vma_is_special_huge(const struct vm_area_struct *vma) > -{ > - return vma_is_dax(vma) || (vma->vm_file && > - (vma->vm_flags & (VM_PFNMAP | VM_MIXED= MAP))); > -} > - > #endif /* CONFIG_TRANSPARENT_HUGEPAGE || CONFIG_HUGETLBFS */ > > #if MAX_NUMNODES > 1 > diff --git a/mm/huge_memory.c b/mm/huge_memory.c > index e90d08db219d..2775309b317a 100644 > --- a/mm/huge_memory.c > +++ b/mm/huge_memory.c > @@ -103,6 +103,14 @@ static inline bool file_thp_enabled(struct vm_area_s= truct *vma) > return !inode_is_open_for_write(inode) && S_ISREG(inode->i_mode); > } > > +/* If returns true, we are unable to access the VMA's folios. */ > +static bool vma_is_special_huge(const struct vm_area_struct *vma) > +{ > + if (vma_is_dax(vma)) > + return false; > + return vma_test_any(vma, VMA_PFNMAP_BIT, VMA_MIXEDMAP_BIT); > +} > + > unsigned long __thp_vma_allowable_orders(struct vm_area_struct *vma, > vm_flags_t vm_flags, > enum tva_type type, > @@ -116,8 +124,8 @@ unsigned long __thp_vma_allowable_orders(struct vm_ar= ea_struct *vma, > /* Check the intersection of requested and supported orders. */ > if (vma_is_anonymous(vma)) > supported_orders =3D THP_ORDERS_ALL_ANON; > - else if (vma_is_special_huge(vma)) > - supported_orders =3D THP_ORDERS_ALL_SPECIAL; > + else if (vma_is_dax(vma) || vma_is_special_huge(vma)) > + supported_orders =3D THP_ORDERS_ALL_SPECIAL_DAX; > else > supported_orders =3D THP_ORDERS_ALL_FILE_DEFAULT; > > @@ -2338,7 +2346,7 @@ int zap_huge_pmd(struct mmu_gather *tlb, struct vm_= area_struct *vma, > tlb->fullmm); > arch_check_zapped_pmd(vma, orig_pmd); > tlb_remove_pmd_tlb_entry(tlb, pmd, addr); > - if (!vma_is_dax(vma) && vma_is_special_huge(vma)) { > + if (vma_is_special_huge(vma)) { > if (arch_needs_pgtable_deposit()) > zap_deposited_table(tlb->mm, pmd); > spin_unlock(ptl); > @@ -2840,7 +2848,7 @@ int zap_huge_pud(struct mmu_gather *tlb, struct vm_= area_struct *vma, > orig_pud =3D pudp_huge_get_and_clear_full(vma, addr, pud, tlb->fu= llmm); > arch_check_zapped_pud(vma, orig_pud); > tlb_remove_pud_tlb_entry(tlb, pud, addr); > - if (!vma_is_dax(vma) && vma_is_special_huge(vma)) { > + if (vma_is_special_huge(vma)) { > spin_unlock(ptl); > /* No zero page support yet */ > } else { > @@ -2991,7 +2999,7 @@ static void __split_huge_pmd_locked(struct vm_area_= struct *vma, pmd_t *pmd, > */ > if (arch_needs_pgtable_deposit()) > zap_deposited_table(mm, pmd); > - if (!vma_is_dax(vma) && vma_is_special_huge(vma)) > + if (vma_is_special_huge(vma)) > return; > if (unlikely(pmd_is_migration_entry(old_pmd))) { > const softleaf_t old_entry =3D softleaf_from_pmd(= old_pmd); > @@ -4517,8 +4525,16 @@ static void split_huge_pages_all(void) > > static inline bool vma_not_suitable_for_thp_split(struct vm_area_struct = *vma) > { > - return vma_is_special_huge(vma) || (vma->vm_flags & VM_IO) || > - is_vm_hugetlb_page(vma); > + if (vma_is_dax(vma)) > + return true; > + if (vma_is_special_huge(vma)) > + return true; > + if (vma_test(vma, VMA_IO_BIT)) > + return true; > + if (is_vm_hugetlb_page(vma)) > + return true; > + > + return false; > } > > static int split_huge_pages_pid(int pid, unsigned long vaddr_start, > -- > 2.53.0 >