From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by smtp.subspace.kernel.org (Postfix) with ESMTP id A5A7128488F for ; Tue, 14 Jul 2026 04:34:58 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=217.140.110.172 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1784003701; cv=none; b=P56U5A7TpN84jeyo3I/eOxHiPuqAWlMAbZBwhA1xr0hzLnqQlOkUjO74kXf/SnuTv5t7BK4K3iDh13fCnpoRrJd+urgtSW7rwI52D0D1WbW6BWvZa56eehR5GqNkdZfIT5Xbo3Uhx6hgB9Ps69KHwQkCb+MX4NKSbjpxvzqKjvU= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1784003701; c=relaxed/simple; bh=BxkWyC9Bhg38Bdzlxk2i0B0fqTApnC3gzsK70rHjD2M=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=mcymRbQ/fW8xRWVPCgVG4Mc4Lcu8CJBHW1IlFLqql6e3QVJBD90EI8KUuIZ2wXgWkULFubhCh2zNUuTjJQfLffUNLlc/OcYnWVz0MYFoW0LYwcDtV6pStuR53Hkyv2SaDyJkurfC6z/ljFDcm2+jF0KTShzBTj7CClh9aKawjOQ= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com; spf=pass smtp.mailfrom=arm.com; dkim=pass (1024-bit key) header.d=arm.com header.i=@arm.com header.b=KwUrnLjz; arc=none smtp.client-ip=217.140.110.172 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=arm.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=arm.com header.i=@arm.com header.b="KwUrnLjz" Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 82C421570; Mon, 13 Jul 2026 21:34:53 -0700 (PDT) Received: from [10.164.148.52] (unknown [10.164.148.52]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 91D583F7B4; Mon, 13 Jul 2026 21:34:53 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=simple/simple; d=arm.com; s=foss; t=1784003697; bh=BxkWyC9Bhg38Bdzlxk2i0B0fqTApnC3gzsK70rHjD2M=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=KwUrnLjzAVWoVjf+esj3MW/phE+xAwE72Ug8zTJ/jqyB6sMXFO9y11RbpKOBGwemy e2us0nCdvNyjzhZPb6pzcu+k41WXpRHoZnHxbjdRcfeXtBzfcMMWgSPzDYpbQfhr+b ybZ0qBZJAfJTQYR1SkfrgB4ot17SfThYt7Oea9PY= Message-ID: Date: Tue, 14 Jul 2026 10:04:44 +0530 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v6 0/6] mm/vmalloc: Speed up ioremap, vmalloc and vmap with contiguous memory To: Uladzislau Rezki Cc: Wen Jiang , Andrew Morton , catalin.marinas@arm.com, linux-mm@kvack.org, will@kernel.org, Xueyuan.chen21@gmail.com, ajd@linux.ibm.com, anshuman.khandual@arm.com, david@kernel.org, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, rppt@kernel.org, ryan.roberts@arm.com, Wen Jiang References: <20260709073823.6643-1-jiangwen6@xiaomi.com> <20260709160805.26e63bae89dd03cf2951104e@linux-foundation.org> <54434a84-51b3-4e3f-988b-6bcbac5a2f42@arm.com> Content-Language: en-US From: Dev Jain In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 13/07/26 11:00 pm, Uladzislau Rezki wrote: > On Mon, Jul 13, 2026 at 08:43:14PM +0530, Dev Jain wrote: >> >> >> On 10/07/26 2:24 pm, Wen Jiang wrote: >>> On Fri, 10 Jul 2026 at 07:08, Andrew Morton wrote: >>>> >>>> On Thu, 9 Jul 2026 15:38:17 +0800 Wen Jiang wrote: >>>> >>>>> This patchset accelerates ioremap, vmalloc, and vmap when the memory >>>>> is physically fully or partially contiguous. >>>> >>>> Thanks, I added this to mm.git's mm-new branch for wider testing. >>>> >>>> AI review asked some questions, and some of them are new since the v5 >>>> series: >>>> https://sashiko.dev/#/patchset/20260709073823.6643-1-jiangwen6@xiaomi.com >>> >>> Hi Andrew, >>> >>> I've gone through the Sashiko findings: >>> >>> - Patch 1 (find_num_contig): Over-interpretation. No new hugetlbfs hstate >>> is added. The extra sizes are only used by init_mm kernel mappings via. >>> >>> - Patch 5/6 (NULL page): Invalid input. vmap() expects a fully populated >>> array of valid struct page pointers. >> >> Correct, but vmap_pages_pte_range has !page and !pfn_valid checks. >> >> I really hate those checks - if those checks have any remote possibility of >> firing, then we already have a bug at >> >> vm_map_ram -> vmap_pages_range -> vmap_pages_range_noflush -> kmsan_vmap_pages_range_noflush >> >> because the last function dereferences the struct page pointers. >> >> It is painful to do the page array sanity check deep into vmap - it implies >> we simply cannot play with the page array before that. >> >> But since vmap is an exported function, doing a sanity check for the page array >> in the vmap code makes sense. >> >> So how about the following: >> >> diff --git a/mm/vmalloc.c b/mm/vmalloc.c >> index afaa14ebf17bb..0c44bb7a45b5d 100644 >> --- a/mm/vmalloc.c >> +++ b/mm/vmalloc.c >> @@ -566,14 +566,6 @@ static int vmap_pages_pte_range(pmd_t *pmd, unsigned long addr, >> err = -EBUSY; >> break; >> } >> - if (WARN_ON(!page)) { >> - err = -ENOMEM; >> - break; >> - } >> - if (WARN_ON(!pfn_valid(page_to_pfn(page)))) { >> - err = -EINVAL; >> - break; >> - } >> >> pfn = page_to_pfn(page); >> size = vmap_set_ptes(pte, addr, end, pfn, prot, shift); >> @@ -603,11 +595,6 @@ static int vmap_pages_pmd_range(pud_t *pud, unsigned long addr, >> 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, >> @@ -3663,6 +3650,19 @@ static struct vm_struct *vmap_get_aligned_vm_area(unsigned long size, >> return __get_vm_area_node_aligned_caller(size, PAGE_SIZE, flags, caller); >> } >> >> +static inline bool vmap_page_sanity_checks(struct page **pages, unsigned int count) >> +{ >> + for (int i = 0; i < count; ++i) { >> + if (WARN_ON(!pages[i])) >> + return true; >> + >> + if (WARN_ON(!pfn_valid(page_to_pfn(pages[i])))) >> + return true; >> + } >> + >> + return false; >> +} >> + >> /** >> * vmap - map an array of pages into virtually contiguous space >> * @pages: array of page pointers >> @@ -3706,6 +3706,9 @@ void *vmap(struct page **pages, unsigned int count, >> if (!area) >> return NULL; >> >> + if (unlikely(vmap_page_sanity_checks(pages, count))) >> + return NULL; >> + >> addr = (unsigned long)area->addr; >> if (vmap_pages_range_batched(addr, addr + size, pgprot_nx(prot), >> pages) < 0) { >> >> >> >> Reasoning for calling vmap_page_sanity_checks() before vmap_pages_range_batched, >> and not at the start of vmap: I am worried that since vmap() is already very >> fast, we may cause a regression: >> >> vmap() -> scan page array with linear map pointers -> vmap_get_aligned_vm_area (does >> memory allocation, throwing out the linear map VAs from cache and TLB) -> walk >> the pgtables and again access cold page array. >> >> Perhaps I am being very pedantic here. What do you think? >> > Sanity check adds extra CPU cycles and it adds overhead. The concern about cache > to be cold on second iteration looks valid. You can get some perf figures to see > the cost. > > I would just keep the original approach. But no strong opinion here. Given you don't have a strong opinion here, I would also prefer keeping the original approach. This feels more like a code structure problem than a correctness problem, *and* given that with kmsan builds we have this problem for years now in the kernel. So perhaps we can look at how to solve this later. > > -- > Uladzislau Rezki