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 56FD212FF69 for ; Wed, 8 Apr 2026 14:03:19 +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=1775657001; cv=none; b=u+4pz7UZYRNZ1NSfaFm+aigltZdzgGS0n3nuoSJm7giE5c+eqfNLn70k8dx4jq0keaTfm46e90TEwqpj53Uf6EdXXe1tDSmdhGvqB3Pw9XWPDl8wRKIKHkSUO+QOxfF24qYqjXv07XExMyp+UJ+dlyCMOr4cFwFN/mtpcc/9uy4= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1775657001; c=relaxed/simple; bh=mBcTI6iP+yGZjitLw/2y8VAoswxzOV+GzQFjaDM+rJE=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=NoieMUmveI82Kw1+4QQ3cM1+DoG/1gxkEkcNjnvuxb6Ctky/+zTvmP2+1UcGglS9xEzF9fy+VrLC9UwHAYgWVu3Y0ZI7ssLKumevRZVi/K28u7zjzL3voi320RCJGz20LjCXjWHILX22HlOVXFOO4Wr8DGctwGQZb+i/Jstw4MM= 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=uF9YVPoA; 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="uF9YVPoA" 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 DB44A267F; Wed, 8 Apr 2026 07:03:12 -0700 (PDT) Received: from [10.164.148.132] (unknown [10.164.148.132]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id E27483F632; Wed, 8 Apr 2026 07:03:13 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=simple/simple; d=arm.com; s=foss; t=1775656998; bh=mBcTI6iP+yGZjitLw/2y8VAoswxzOV+GzQFjaDM+rJE=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=uF9YVPoAWLM3ZMXDgsdRN7uBAZmC4m2DTAjbtsmHJSmKIqlnn0hpH/YV/zwN+CwCY 9Rv5VIummHWSwrF7YZboLxLu4ZY72hI3IuiMkoAaxfrPO3L6LgDecLOjy+RbhddIk4 kEdfUxyC3bvZI/toZbKG/FmOS94Lwrw731gFOf4Q= Message-ID: Date: Wed, 8 Apr 2026 19:33:01 +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: [RFC PATCH 5/8] mm/vmalloc: map contiguous pages in batches for vmap() if possible To: "Barry Song (Xiaomi)" , linux-mm@kvack.org, linux-arm-kernel@lists.infradead.org, catalin.marinas@arm.com, will@kernel.org, akpm@linux-foundation.org, urezki@gmail.com Cc: linux-kernel@vger.kernel.org, anshuman.khandual@arm.com, ryan.roberts@arm.com, ajd@linux.ibm.com, rppt@kernel.org, david@kernel.org, Xueyuan.chen21@gmail.com References: <20260408025115.27368-1-baohua@kernel.org> <20260408025115.27368-6-baohua@kernel.org> Content-Language: en-US From: Dev Jain In-Reply-To: <20260408025115.27368-6-baohua@kernel.org> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit On 08/04/26 8:21 am, Barry Song (Xiaomi) wrote: > In many cases, the pages passed to vmap() may include high-order > pages allocated with __GFP_COMP flags. For example, the systemheap > often allocates pages in descending order: order 8, then 4, then 0. > Currently, vmap() iterates over every page individually—even pages > inside a high-order block are handled one by one. > > This patch detects high-order pages and maps them as a single > contiguous block whenever possible. > > An alternative would be to implement a new API, vmap_sg(), but that > change seems to be large in scope. > > Signed-off-by: Barry Song (Xiaomi) > --- > mm/vmalloc.c | 51 +++++++++++++++++++++++++++++++++++++++++++++++++-- > 1 file changed, 49 insertions(+), 2 deletions(-) > > diff --git a/mm/vmalloc.c b/mm/vmalloc.c > index eba436386929..e8dbfada42bc 100644 > --- a/mm/vmalloc.c > +++ b/mm/vmalloc.c > @@ -3529,6 +3529,53 @@ void vunmap(const void *addr) > } > EXPORT_SYMBOL(vunmap); > > +static inline int get_vmap_batch_order(struct page **pages, > + unsigned int max_steps, unsigned int idx) > +{ > + unsigned int nr_pages; > + > + if (!IS_ENABLED(CONFIG_HAVE_ARCH_HUGE_VMAP) || > + ioremap_max_page_shift == PAGE_SHIFT) > + return 0; > + > + nr_pages = compound_nr(pages[idx]); > + if (nr_pages == 1 || max_steps < nr_pages) > + return 0; This assumes that the page array passed to vmap() will have compound pages if it is a higher order allocation. See rb_alloc_aux_page(). It gets higher-order allocations without passing GFP_COMP. That is why my implementation does not assume anything about the property of the pages. Also it may be useful to do regression-testing for the common case of vmap() with a single page (assuming it is common, I don't know), in which case we may have to special case it. My implementation requires opting in with VM_ALLOW_HUGE_VMAP - I suspect you may run into problems if you make vmap() do huge-mappings as best-effort by default. I am guessing this because ... Drivers can operate on individual pages, so vmalloc() calls split_page() and then does the block/cont mappings. This same issue should be present with vmap() too? In which case if we are to do huge-mappings by default then we can do split_page() after detecting contiguous chunks. But ... that may create problems for the caller of vmap() - vmap now has the changed the properties of the pages. > + > + if (num_pages_contiguous(&pages[idx], nr_pages) == nr_pages) > + return compound_order(pages[idx]); > + return 0; > +} > + > +static int vmap_contig_pages_range(unsigned long addr, unsigned long end, > + pgprot_t prot, struct page **pages) > +{ > + unsigned int count = (end - addr) >> PAGE_SHIFT; > + int err; > + > + err = kmsan_vmap_pages_range_noflush(addr, end, prot, pages, > + PAGE_SHIFT, GFP_KERNEL); > + if (err) > + goto out; > + > + for (unsigned int i = 0; i < count; ) { > + unsigned int shift = PAGE_SHIFT + > + get_vmap_batch_order(pages, count - i, i); > + > + err = vmap_range_noflush(addr, addr + (1UL << shift), > + page_to_phys(pages[i]), prot, shift); > + if (err) > + goto out; > + > + addr += 1UL << shift; > + i += 1U << (shift - PAGE_SHIFT); > + } > + > +out: > + flush_cache_vmap(addr, end); > + return err; > +} > + > /** > * vmap - map an array of pages into virtually contiguous space > * @pages: array of page pointers > @@ -3572,8 +3619,8 @@ void *vmap(struct page **pages, unsigned int count, > return NULL; > > addr = (unsigned long)area->addr; > - if (vmap_pages_range(addr, addr + size, pgprot_nx(prot), > - pages, PAGE_SHIFT) < 0) { > + if (vmap_contig_pages_range(addr, addr + size, pgprot_nx(prot), > + pages) < 0) { > vunmap(area->addr); > return NULL; > }