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h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=WQvDMaFUXNSK+QfT0babDWN0PqczaocaeP11xLDjWIwm6SxkeZIALqX7/gr6y3q7k MiS7e2ST/Ug55d4/EbZVFBvcHh5Js9O7gnzQwz3jQLJD3XAlukINZVZdaO7k7+onST I2030DWVL9Pyf0pTwWclD2zoRkH01zfhwaAxPZLE= Message-ID: <53a51128-8ad5-4faa-9151-1245084bdd4c@arm.com> Date: Fri, 5 Jun 2026 11:32:37 +0530 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3 4/6] mm/vmalloc: Extend page table walk to support larger page_shift sizes and eliminate page table rewalk To: Wen Jiang Cc: linux-mm@kvack.org, linux-arm-kernel@lists.infradead.org, catalin.marinas@arm.com, will@kernel.org, akpm@linux-foundation.org, urezki@gmail.com, baohua@kernel.org, Xueyuan.chen21@gmail.com, rppt@kernel.org, david@kernel.org, ryan.roberts@arm.com, anshuman.khandual@arm.com, ajd@linux.ibm.com, linux-kernel@vger.kernel.org, jiangwen6@xiaomi.com References: <20260522053146.83209-1-jiangwenxiaomi@gmail.com> <20260522053146.83209-5-jiangwenxiaomi@gmail.com> <46b0f2a7-3c0d-4372-a45d-946d8259d410@arm.com> Content-Language: en-US From: Dev Jain In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam06 X-Rspamd-Queue-Id: B8CE614000A X-Stat-Signature: nzx9bfq134dgs8pnki77bmwghixdw97y X-Rspam-User: X-HE-Tag: 1780639367-956721 X-HE-Meta: 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 vGHTKn+c WahHa2LheYbM1FBAJnVY5t/0eniGptHonYY0tNHLqA0VPFfavUk0ji69wB3jmlXxop9Ftmyj2w1fIIGYVDO1r3AOLswgR95p3R+LjVq2s5f5i6GCf11ZM4xLvE+VWoPDN999BVvv1/hPAJRIQ1vinNQXWvukQdMx5SHmVUJ6MjM3AWBXT9AsfdPbUqd51uJruLjnYW17Nt+xvAcbiWbCh3mDS95yH1JJ1LXn9rUxqUFn6Dmhw6nac5kEHeS0bcdqYNY3LBAZYtZMLJKjHqGQ9zQk8UNi8OF5jKKBuKz95thvXB5G1qxuU3dEcbB6DwptgrNbYdjLJm+upmnnLKx5a6RcuhGTabwg6UvNrTOQao+wdcLL7+m1ho45U9i1HuSD3mb4kxsh++ophH8Pl5QYCYDfbyN8UUy0PzgX7r/yeNGlm5VPxKEL9ukv1CrCYCyMCyG7Hy02r4ln4gQfFQaBdkRi0+qaF4Wx9gO1Qfu/s57p6vUE= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 28/05/26 9:09 am, Wen Jiang wrote: > On Wed, 27 May 2026 at 13:59, Dev Jain wrote: >> >> >> >> On 22/05/26 11:01 am, 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 >> --- >> mm/vmalloc.c | 71 +++++++++++++++++++++++++++++----------------------- >> 1 file changed, 40 insertions(+), 31 deletions(-) >> >> diff --git a/mm/vmalloc.c b/mm/vmalloc.c >> index 53fd4ee460ea4..deb764abc0571 100644 >> --- a/mm/vmalloc.c >> +++ b/mm/vmalloc.c >> @@ -543,8 +543,10 @@ 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; >> >> @@ -575,9 +577,10 @@ 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); >> >> lazy_mmu_mode_disable(); >> *mask |= PGTBL_PTE_MODIFIED; >> @@ -587,7 +590,7 @@ 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; >>> @@ -597,7 +600,27 @@ static int vmap_pages_pmd_range(pud_t *pud, unsigned long addr, >>> return -ENOMEM; >>> do { >>> next = pmd_addr_end(addr, end); >>> - if (vmap_pages_pte_range(pmd, addr, next, prot, pages, nr, mask)) >>> + >>> + 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; >> >> >> So I know these !page and !pfn_valid checks have been copied from vmap_pages_pte_range, >> but do they mean anything? >> >> I think pfn_valid() makes sense in that someone may take a random VA/PA, convert it into a struct >> page and pass to vmap layer. But I don't see how anyone would pass page == NULL? At the >> very least, returning ENOMEM does not make sense because the pages are not being >> allocated by vmap() but have already been allocated. > > Hi Dev, > > vmap() is EXPORT_SYMBOL with many callers across drivers, each > constructing the pages array differently. The !page check guards > against malformed arrays at this API boundary. > > The same -ENOMEM issue also exists in vmap_pages_pte_range(). > Should I fix both in this patchset or leave it as a separate cleanup? > >> >>> + >>> + phys_addr = page_to_phys(page); >>> + >>> + if (vmap_try_huge_pmd(pmd, addr, next, phys_addr, prot, >>> + shift)) { >>> + *mask |= PGTBL_PMD_MODIFIED; >>> + *nr += 1 << (shift - PAGE_SHIFT); >>> + continue; >>> + } >>> + } >>> + >>> + if (vmap_pages_pte_range(pmd, addr, next, prot, pages, nr, mask, shift)) >>> return -ENOMEM; >>> } while (pmd++, addr = next, addr != end); >>> return 0; >>> @@ -605,7 +628,7 @@ static int vmap_pages_pmd_range(pud_t *pud, unsigned long addr, >>> >>> 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; >>> @@ -615,7 +638,7 @@ static int vmap_pages_pud_range(p4d_t *p4d, unsigned long addr, >>> return -ENOMEM; >>> do { >>> next = pud_addr_end(addr, end); >>> - if (vmap_pages_pmd_range(pud, addr, next, prot, pages, nr, mask)) >>> + if (vmap_pages_pmd_range(pud, addr, next, prot, pages, nr, mask, shift)) >>> return -ENOMEM; >>> } while (pud++, addr = next, addr != end); >>> return 0; >>> @@ -623,7 +646,7 @@ static int vmap_pages_pud_range(p4d_t *p4d, unsigned long addr, >>> >>> 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; >>> @@ -633,14 +656,14 @@ static int vmap_pages_p4d_range(pgd_t *pgd, unsigned long addr, >>> return -ENOMEM; >>> do { >>> next = p4d_addr_end(addr, end); >>> - if (vmap_pages_pud_range(p4d, addr, next, prot, pages, nr, mask)) >>> + if (vmap_pages_pud_range(p4d, addr, next, prot, pages, nr, mask, shift)) >>> return -ENOMEM; >>> } 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) >>> +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; >>> @@ -655,7 +678,7 @@ 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); >>> @@ -678,27 +701,13 @@ 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); >>> >>> - if (!IS_ENABLED(CONFIG_HAVE_ARCH_HUGE_VMALLOC) || >>> - page_shift == PAGE_SHIFT) >>> - return vmap_small_pages_range_noflush(addr, end, prot, pages); >>> + if (!IS_ENABLED(CONFIG_HAVE_ARCH_HUGE_VMALLOC)) >>> + page_shift = PAGE_SHIFT; >>> >>> - for (i = 0; i < nr; i += 1U << (page_shift - PAGE_SHIFT)) { >>> - int err; >>> - >>> - err = vmap_range_noflush(addr, addr + (1UL << page_shift), >>> - page_to_phys(pages[i]), prot, >>> - page_shift); >>> - if (err) >>> - return err; >>> - >>> - addr += 1UL << page_shift; >>> - } >>> - >>> - return 0; >>> + return vmap_pages_range_noflush_walk(addr, end, prot, pages, >>> + min(page_shift, PMD_SHIFT)); >> >> >> We can easily extend to PUD huge mappings right? Not sure whether we >> should keep everything symmetric to how vmap_range_noflush() operates >> right now, since P4D mappings don't exist, but PUD looks worthwhile. >> > > PUD mapping requires 1GB of contiguous physical memory, but the buddy > allocator's MAX_PAGE_ORDER is 10 (4MB on 4K pages). So page_shift > passed to vmap_pages_range_noflush_walk() never exceeds PMD_SHIFT. Can we then just drop the min()? You can guard the try_huge_pmd with shift >= PMD_SHIFT - the walker has the necessary ingredients to work with a shift > PMD_SHIFT, so let us not confuse by this min() truncation. > > Thanks, > Wen >>> } >>> >>> int vmap_pages_range_noflush(unsigned long addr, unsigned long end, >>