From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-ig0-f181.google.com (mail-ig0-f181.google.com [209.85.213.181]) by kanga.kvack.org (Postfix) with ESMTP id 69FB56B007E for ; Thu, 31 Mar 2016 12:32:34 -0400 (EDT) Received: by mail-ig0-f181.google.com with SMTP id nk17so130272381igb.1 for ; Thu, 31 Mar 2016 09:32:34 -0700 (PDT) Received: from aserp1040.oracle.com (aserp1040.oracle.com. [141.146.126.69]) by mx.google.com with ESMTPS id v71si7874342ioi.24.2016.03.31.09.32.32 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Thu, 31 Mar 2016 09:32:33 -0700 (PDT) Subject: Re: [RFC PATCH 2/2] x86/hugetlb: Attempt PUD_SIZE mapping alignment if PMD sharing enabled References: <1459213970-17957-1-git-send-email-mike.kravetz@oracle.com> <1459213970-17957-3-git-send-email-mike.kravetz@oracle.com> <20160329083510.GA27941@gmail.com> <56FAB5DB.8070003@oracle.com> <20160331022655.GA24293@hori1.linux.bs1.fc.nec.co.jp> From: Mike Kravetz Message-ID: <56FD5106.90002@oracle.com> Date: Thu, 31 Mar 2016 09:32:06 -0700 MIME-Version: 1.0 In-Reply-To: <20160331022655.GA24293@hori1.linux.bs1.fc.nec.co.jp> Content-Type: text/plain; charset=iso-2022-jp Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Naoya Horiguchi Cc: Ingo Molnar , "linux-mm@kvack.org" , "linux-kernel@vger.kernel.org" , "x86@kernel.org" , Hugh Dickins , Hillf Danton , "Kirill A. Shutemov" , David Rientjes , Dave Hansen , Thomas Gleixner , Ingo Molnar , "H. Peter Anvin" , Catalin Marinas , Will Deacon , Steve Capper , Andrew Morton On 03/30/2016 07:26 PM, Naoya Horiguchi wrote: > On Tue, Mar 29, 2016 at 10:05:31AM -0700, Mike Kravetz wrote: >> On 03/29/2016 01:35 AM, Ingo Molnar wrote: >>> >>> * Mike Kravetz wrote: >>> >>>> When creating a hugetlb mapping, attempt PUD_SIZE alignment if the >>>> following conditions are met: >>>> - Address passed to mmap or shmat is NULL >>>> - The mapping is flaged as shared >>>> - The mapping is at least PUD_SIZE in length >>>> If a PUD_SIZE aligned mapping can not be created, then fall back to a >>>> huge page size mapping. >>>> >>>> Signed-off-by: Mike Kravetz >>>> --- >>>> arch/x86/mm/hugetlbpage.c | 64 ++++++++++++++++++++++++++++++++++++++++++++--- >>>> 1 file changed, 61 insertions(+), 3 deletions(-) >>>> >>>> diff --git a/arch/x86/mm/hugetlbpage.c b/arch/x86/mm/hugetlbpage.c >>>> index 42982b2..4f53af5 100644 >>>> --- a/arch/x86/mm/hugetlbpage.c >>>> +++ b/arch/x86/mm/hugetlbpage.c >>>> @@ -78,14 +78,39 @@ static unsigned long hugetlb_get_unmapped_area_bottomup(struct file *file, >>>> { >>>> struct hstate *h = hstate_file(file); >>>> struct vm_unmapped_area_info info; >>>> + bool pud_size_align = false; >>>> + unsigned long ret_addr; >>>> + >>>> + /* >>>> + * If PMD sharing is enabled, align to PUD_SIZE to facilitate >>>> + * sharing. Only attempt alignment if no address was passed in, >>>> + * flags indicate sharing and size is big enough. >>>> + */ >>>> + if (IS_ENABLED(CONFIG_ARCH_WANT_HUGE_PMD_SHARE) && >>>> + !addr && flags & MAP_SHARED && len >= PUD_SIZE) >>>> + pud_size_align = true; >>>> >>>> info.flags = 0; >>>> info.length = len; >>>> info.low_limit = current->mm->mmap_legacy_base; >>>> info.high_limit = TASK_SIZE; >>>> - info.align_mask = PAGE_MASK & ~huge_page_mask(h); >>>> + if (pud_size_align) >>>> + info.align_mask = PAGE_MASK & (PUD_SIZE - 1); >>>> + else >>>> + info.align_mask = PAGE_MASK & ~huge_page_mask(h); >>>> info.align_offset = 0; >>>> - return vm_unmapped_area(&info); >>>> + ret_addr = vm_unmapped_area(&info); >>>> + >>>> + /* >>>> + * If failed with PUD_SIZE alignment, try again with huge page >>>> + * size alignment. >>>> + */ >>>> + if ((ret_addr & ~PAGE_MASK) && pud_size_align) { >>>> + info.align_mask = PAGE_MASK & ~huge_page_mask(h); >>>> + ret_addr = vm_unmapped_area(&info); >>>> + } >>> >>> So AFAICS 'ret_addr' is either page aligned, or is an error code. Wouldn't it be a >>> lot easier to read to say: >>> >>> if ((long)ret_addr > 0 && pud_size_align) { >>> info.align_mask = PAGE_MASK & ~huge_page_mask(h); >>> ret_addr = vm_unmapped_area(&info); >>> } >>> >>> return ret_addr; >>> >>> to make it clear that it's about error handling, not some alignment >>> requirement/restriction? >> >> Yes, I agree that is easier to read. However, it assumes that process >> virtual addresses can never evaluate to a negative long value. This may >> be the case for x86_64 today. But, there are other architectures where >> this is not the case. I know this is x86 specific code, but might it be >> possible that x86 virtual addresses could be negative longs in the future? >> >> It appears that all callers of vm_unmapped_area() are using the page aligned >> check to determine error. I would prefer to do the same, and can add >> comments to make that more clear. > > IS_ERR_VALUE() might be helpful? > Thanks Naoya, I'll change all this to use IS_ERR_VALUE(). -- Mike Kravetz -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org