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 837E5264FBD for ; Wed, 27 May 2026 08:28:03 +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=1779870485; cv=none; b=tAPRzRO923xVWIFp0bq+0NKJMl8GRbXP/g8dqJzTSbBQHYk9W6f6gcXnVkF5TzUFQEVefwW/WqK1dPd5mO8pp4TZrA/HpQAPMIxRgXzSpCO1KSG3YIz3FwC6OQxhaaKraQblBqRqWBQcbtWBCSFI+TuBPu3ffY6Mnpnm14AcTFw= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1779870485; c=relaxed/simple; bh=zqMwayjvGNQaNb1jqTGaRplGikMOmx9Kmixu6dv1Veo=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=MFK+aNKJk0AUkZnFeIYQAJJc5AYkfL7yEMoUoNMORzLOuzCHcbQgMvVD3qUnBHv8H4AaxS7jPW+QQOrtW/z6yi9GZlF5eUZvHxRVl/V/XPrNgxtiZrrHzaj1lq/f1eD/rWo577ePpGFklEqXRqabiscteDJjlg/Knht0HopHBoo= 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=QHsKKMwG; 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="QHsKKMwG" 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 DAE082880; Wed, 27 May 2026 01:27:57 -0700 (PDT) Received: from [10.164.19.7] (unknown [10.164.19.7]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id DA27D3F7D8; Wed, 27 May 2026 01:27:57 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=simple/simple; d=arm.com; s=foss; t=1779870482; bh=zqMwayjvGNQaNb1jqTGaRplGikMOmx9Kmixu6dv1Veo=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=QHsKKMwGP18WsqNGBObxNHu/wRN2qzvaTMPP6VCByY/l1/dY9p7BMOCdN3lJW9zPz fr9zo2x4dzUU8sEebR42jOwW/Z66FwdWXVTpvlSM6hOL8ouhtWjOHrbcc1HzUrweVS CwRvhY6w9YNz4xyH0T+cn0bWSm0lGsUspT7ebhYs= Message-ID: <340c811e-2501-46c3-8a55-19e955c5ae8a@arm.com> Date: Wed, 27 May 2026 13:57:54 +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 v3 5/6] mm/vmalloc: map contiguous pages in batches for vmap() if possible To: Wen Jiang , 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: 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> <20260522053146.83209-6-jiangwenxiaomi@gmail.com> Content-Language: en-US From: Dev Jain In-Reply-To: <20260522053146.83209-6-jiangwenxiaomi@gmail.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit On 22/05/26 11:01 am, Wen Jiang wrote: > From: "Barry Song (Xiaomi)" > > In many cases, the pages passed to vmap() may include high-order > pages. 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 physically contiguous pages (regardless of whether > they are compound or non-compound) by scanning with > num_pages_contiguous(), and maps them as a single contiguous block > whenever possible. The first page's pfn must be aligned to the > mapping order for the batched mapping to be used. > > Pages with the same page_shift are coalesced and mapped via > vmap_pages_range_noflush_walk() to avoid page table rewalk. > > As users typically allocate memory in descending orders (e.g. > 8 → 4 → 0), once an order-0 page is encountered, we stop scanning > for contiguous pages since subsequent pages are likely order-0 as well. > > Signed-off-by: Barry Song (Xiaomi) > Co-developed-by: Dev Jain > Signed-off-by: Dev Jain > Signed-off-by: Wen Jiang > Tested-by: Xueyuan Chen > --- > mm/vmalloc.c | 82 ++++++++++++++++++++++++++++++++++++++++++++++++++-- > 1 file changed, 80 insertions(+), 2 deletions(-) > > diff --git a/mm/vmalloc.c b/mm/vmalloc.c > index deb764abc0571..50642246f4d40 100644 > --- a/mm/vmalloc.c > +++ b/mm/vmalloc.c > @@ -3542,6 +3542,84 @@ 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_contig; > + int order; > + > + if (!IS_ENABLED(CONFIG_HAVE_ARCH_HUGE_VMAP) || > + ioremap_max_page_shift == PAGE_SHIFT) Why bail out on ioremap_max_page_shift == PAGE_SHIFT? The code path for ioremap is different from vmap right? > + return 0; > + > + nr_contig = num_pages_contiguous(&pages[idx], max_steps); > + if (nr_contig < 2) > + return 0; > + > + order = fls(nr_contig) - 1; > + > + if (arch_vmap_pte_supported_shift(PAGE_SIZE << order) == PAGE_SHIFT) > + return 0; > + > + /* Ensure the first page's pfn is aligned to the order */ > + if (!IS_ALIGNED(page_to_pfn(pages[idx]), 1 << order)) > + return 0; > + > + return order; > +} > + > +static int vmap_batched(unsigned long addr, unsigned long end, > + pgprot_t prot, struct page **pages) > +{ > + unsigned int count = (end - addr) >> PAGE_SHIFT; > + unsigned int prev_shift = 0, idx = 0; > + unsigned long start = addr, map_addr = addr; > + 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); > + > + if (!i) > + prev_shift = shift; > + > + if (shift != prev_shift) { > + err = vmap_pages_range_noflush_walk(map_addr, addr, It would be worth documenting vmap_pages_range_noflush_walk() that it can take an array of pages which are not all contiguous, but it may have contiguous chunks, as hinted by page_shift. Otherwise this looks good. > + prot, pages + idx, > + min(prev_shift, PMD_SHIFT)); > + if (err) > + goto out; > + prev_shift = shift; > + map_addr = addr; > + idx = i; > + } > + > + /* > + * Once small pages are encountered, the remaining pages > + * are likely small as well. > + */ > + if (shift == PAGE_SHIFT) > + break; > + > + addr += 1UL << shift; > + i += 1U << (shift - PAGE_SHIFT); > + } > + > + /* Remaining */ > + if (map_addr < end) > + err = vmap_pages_range_noflush_walk(map_addr, end, > + prot, pages + idx, min(prev_shift, PMD_SHIFT)); > + > +out: > + flush_cache_vmap(start, end); > + return err; > +} > + > /** > * vmap - map an array of pages into virtually contiguous space > * @pages: array of page pointers > @@ -3585,8 +3663,8 @@ 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_batched(addr, addr + size, pgprot_nx(prot), > + pages) < 0) { > vunmap(area->addr); > return NULL; > }