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Wed, 30 Sep 2026 08:16:11 -0700 (PDT) Received: from milan ([2001:9b1:d5a0:a500::24b]) by smtp.gmail.com with ESMTPSA id a640c23a62f3a-c2e31ce9e4fsm21985066b.31.2026.09.30.08.16.09 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 30 Sep 2026 08:16:11 -0700 (PDT) From: Uladzislau Rezki X-Google-Original-From: Uladzislau Rezki Date: Wed, 30 Sep 2026 17:16:08 +0200 To: Wen Jiang Cc: akpm@linux-foundation.org, catalin.marinas@arm.com, linux-mm@kvack.org, urezki@gmail.com, will@kernel.org, Xueyuan.chen21@gmail.com, ajd@linux.ibm.com, anshuman.khandual@arm.com, baohua@kernel.org, chleroy@kernel.org, david@kernel.org, dev.jain@arm.com, jiangwen6@xiaomi.com, leo.yan@arm.com, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, maddy@linux.ibm.com, mpe@ellerman.id.au, npiggin@gmail.com, rppt@kernel.org, ryan.roberts@arm.com Subject: Re: [PATCH v9 07/10] mm/vmalloc: extend page table walk to support larger page_shift sizes and eliminate page table rewalk Message-ID: References: <20260923062832.479455-1-jiangwen6@xiaomi.com> <20260923062832.479455-8-jiangwen6@xiaomi.com> X-Mailing-List: linuxppc-dev@lists.ozlabs.org List-Id: List-Help: List-Owner: List-Post: List-Archive: , List-Subscribe: , , List-Unsubscribe: Precedence: list MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260923062832.479455-8-jiangwen6@xiaomi.com> On Wed, Sep 23, 2026 at 02:28:29PM +0800, Wen Jiang wrote: > From: "Barry Song (Xiaomi)" > > vmap_pages_range_noflush_walk() (formerly vmap_small_pages_range_noflush()) > provides a clean interface by taking struct page **pages and mapping them > via direct PTE iteration. This avoids the page table rewalk seen when > using vmap_range_noflush() for page_shift values other than PAGE_SHIFT. > > Extend it to support larger page_shift values, and add PMD- and > contiguous-PTE mappings as well. > > Rename it to vmap_pages_range_noflush_walk() since it now handles > more than just small pages. > > For vmalloc() allocations with VM_ALLOW_HUGE_VMAP, we no longer need to > iterate over pages one by one via vmap_range_noflush(), which would > otherwise lead to page table rewalk. The code is now unified with the > PAGE_SHIFT case by simply calling vmap_pages_range_noflush_walk(). > > Signed-off-by: Barry Song (Xiaomi) > Signed-off-by: Wen Jiang > Tested-by: Xueyuan Chen > Tested-by: Leo Yan > Reviewed-by: Dev Jain > --- > mm/vmalloc.c | 84 +++++++++++++++++++++++++++++++--------------------- > 1 file changed, 50 insertions(+), 34 deletions(-) > > diff --git a/mm/vmalloc.c b/mm/vmalloc.c > index d475e52110e4a..6e0dec73107a7 100644 > --- a/mm/vmalloc.c > +++ b/mm/vmalloc.c > @@ -558,8 +558,10 @@ void vunmap_range(unsigned long addr, unsigned long end) > > static int vmap_pages_pte_range(pmd_t *pmd, unsigned long addr, > unsigned long end, pgprot_t prot, struct page **pages, int *nr, > - pgtbl_mod_mask *mask) > + pgtbl_mod_mask *mask, unsigned int shift) > { > + unsigned long pfn, size; > + unsigned int steps; > int err = 0; > pte_t *pte; > > @@ -590,9 +592,10 @@ static int vmap_pages_pte_range(pmd_t *pmd, unsigned long addr, > break; > } > > - set_pte_at(&init_mm, addr, pte, mk_pte(page, prot)); > - (*nr)++; > - } while (pte++, addr += PAGE_SIZE, addr != end); > + pfn = page_to_pfn(page); > + size = vmap_set_ptes(pte, addr, end, pfn, prot, shift); > + steps = PFN_DOWN(size); > + } while (pte += steps, *nr += steps, addr += size, addr != end); > nr_mapped_pages? > > lazy_mmu_mode_disable(); > *mask |= PGTBL_PTE_MODIFIED; > @@ -602,60 +605,88 @@ static int vmap_pages_pte_range(pmd_t *pmd, unsigned long addr, > > static int vmap_pages_pmd_range(pud_t *pud, unsigned long addr, > unsigned long end, pgprot_t prot, struct page **pages, int *nr, > - pgtbl_mod_mask *mask) > + pgtbl_mod_mask *mask, unsigned int shift) > { > pmd_t *pmd; > unsigned long next; > + int err; > > pmd = pmd_alloc_track(&init_mm, pud, addr, mask); > if (!pmd) > return -ENOMEM; > do { > next = pmd_addr_end(addr, end); > - if (vmap_pages_pte_range(pmd, addr, next, prot, pages, nr, mask)) > - return -ENOMEM; > + > + if (shift >= PMD_SHIFT) { > + struct page *page = pages[*nr]; > + phys_addr_t phys_addr; > + > + if (WARN_ON(!page)) > + return -ENOMEM; > + if (WARN_ON(!pfn_valid(page_to_pfn(page)))) > + return -EINVAL; > + > + phys_addr = page_to_phys(page); > + > + if (vmap_try_huge_pmd(pmd, addr, next, phys_addr, prot, shift)) { > + *mask |= PGTBL_PMD_MODIFIED; > + *nr += 1 << (PMD_SHIFT - PAGE_SHIFT); > *nr += 1 << (PMD_SHIFT - PAGE_SHIFT); ---> *nr += 1U << (PMD_SHIFT - PAGE_SHIFT); as it used to be? > + continue; > + } > + } > + err = vmap_pages_pte_range(pmd, addr, next, prot, pages, nr, mask, shift); > + if (err) > + return err; > } while (pmd++, addr = next, addr != end); > return 0; > } > > static int vmap_pages_pud_range(p4d_t *p4d, unsigned long addr, > unsigned long end, pgprot_t prot, struct page **pages, int *nr, > - pgtbl_mod_mask *mask) > + pgtbl_mod_mask *mask, unsigned int shift) > { > pud_t *pud; > unsigned long next; > + int err; > > pud = pud_alloc_track(&init_mm, p4d, addr, mask); > if (!pud) > return -ENOMEM; > do { > next = pud_addr_end(addr, end); > - if (vmap_pages_pmd_range(pud, addr, next, prot, pages, nr, mask)) > - return -ENOMEM; > + err = vmap_pages_pmd_range(pud, addr, next, prot, pages, nr, mask, shift); > + if (err) > + return err; > } while (pud++, addr = next, addr != end); > return 0; > } > > static int vmap_pages_p4d_range(pgd_t *pgd, unsigned long addr, > unsigned long end, pgprot_t prot, struct page **pages, int *nr, > - pgtbl_mod_mask *mask) > + pgtbl_mod_mask *mask, unsigned int shift) > { > p4d_t *p4d; > unsigned long next; > + int err; > > p4d = p4d_alloc_track(&init_mm, pgd, addr, mask); > if (!p4d) > return -ENOMEM; > do { > next = p4d_addr_end(addr, end); > - if (vmap_pages_pud_range(p4d, addr, next, prot, pages, nr, mask)) > - return -ENOMEM; > + err = vmap_pages_pud_range(p4d, addr, next, prot, pages, nr, mask, shift); > + if (err) > + return err; > } while (p4d++, addr = next, addr != end); > return 0; > } > > -static int vmap_small_pages_range_noflush(unsigned long addr, unsigned long end, > - pgprot_t prot, struct page **pages) > +/* > + * It can take an array of pages which are not all contiguous, but it > + * may have contiguous chunks, as hinted by @shift. > + */ > +static int vmap_pages_range_noflush_walk(unsigned long addr, unsigned long end, > + pgprot_t prot, struct page **pages, unsigned int shift) > { > unsigned long start = addr; > pgd_t *pgd; > @@ -670,7 +701,7 @@ static int vmap_small_pages_range_noflush(unsigned long addr, unsigned long end, > next = pgd_addr_end(addr, end); > if (pgd_bad(*pgd)) > mask |= PGTBL_PGD_MODIFIED; > - err = vmap_pages_p4d_range(pgd, addr, next, prot, pages, &nr, &mask); > + err = vmap_pages_p4d_range(pgd, addr, next, prot, pages, &nr, &mask, shift); > if (err) > break; > } while (pgd++, addr = next, addr != end); > @@ -693,27 +724,12 @@ static int vmap_small_pages_range_noflush(unsigned long addr, unsigned long end, > int __vmap_pages_range_noflush(unsigned long addr, unsigned long end, > pgprot_t prot, struct page **pages, unsigned int page_shift) > { > - unsigned int i, nr = (end - addr) >> PAGE_SHIFT; > - > WARN_ON(page_shift < PAGE_SHIFT); > This is not about this patch but probably on that WARN_ON we should bail out early. -- Uladzislau Rezki