From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S934209AbcBQKbI (ORCPT ); Wed, 17 Feb 2016 05:31:08 -0500 Received: from userp1040.oracle.com ([156.151.31.81]:51695 "EHLO userp1040.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S933935AbcBQKbF (ORCPT ); Wed, 17 Feb 2016 05:31:05 -0500 Subject: Re: [PATCH] mm/hugetlb: Fix incorrect proc nr_hugepages value To: "Kirill A. Shutemov" References: <1455651806-25977-1-git-send-email-vaishali.thakkar@oracle.com> <20160217095935.GA15769@node.shutemov.name> Cc: Andrew Morton , n-horiguchi@ah.jp.nec.com, mike.kravetz@oracle.com, hillf.zj@alibaba-inc.com, kirill.shutemov@linux.intel.com, dave.hansen@linux.intel.com, paul.gortmaker@windriver.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org From: Vaishali Thakkar Message-ID: <56C44BC0.1000104@oracle.com> Date: Wed, 17 Feb 2016 16:00:24 +0530 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.4.0 MIME-Version: 1.0 In-Reply-To: <20160217095935.GA15769@node.shutemov.name> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit X-Source-IP: aserv0021.oracle.com [141.146.126.233] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wednesday 17 February 2016 03:29 PM, Kirill A. Shutemov wrote: > On Wed, Feb 17, 2016 at 01:13:26AM +0530, Vaishali Thakkar wrote: >> Currently incorrect default hugepage pool size is reported by proc >> nr_hugepages when number of pages for the default huge page size is >> specified twice. >> >> When multiple huge page sizes are supported, /proc/sys/vm/nr_hugepages >> indicates the current number of pre-allocated huge pages of the default >> size. Basically /proc/sys/vm/nr_hugepages displays default_hstate-> >> max_huge_pages and after boot time pre-allocation, max_huge_pages should >> equal the number of pre-allocated pages (nr_hugepages). >> >> Test case: >> >> Note that this is specific to x86 architecture. >> >> Boot the kernel with command line option 'default_hugepagesz=1G >> hugepages=X hugepagesz=2M hugepages=Y hugepagesz=1G hugepages=Z'. After >> boot, 'cat /proc/sys/vm/nr_hugepages' and 'sysctl -a | grep hugepages' >> returns the value X. However, dmesg output shows that Z huge pages were >> pre-allocated. >> >> So, the root cause of the problem here is that the global variable >> default_hstate_max_huge_pages is set if a default huge page size is >> specified (directly or indirectly) on the command line. After the >> command line processing in hugetlb_init, if default_hstate_max_huge_pages >> is set, the value is assigned to default_hstae.max_huge_pages. However, >> default_hstate.max_huge_pages may have already been set based on the >> number of pre-allocated huge pages of default_hstate size. >> >> The solution to this problem is if hstate->max_huge_pages is already set >> then it should not set as a result of global max_huge_pages value. >> Basically if the value of the variable hugepages is set multiple times >> on a command line for a specific supported hugepagesize then proc layer >> should consider the last specified value. >> >> Signed-off-by: Vaishali Thakkar >> --- >> The patch contains one line over 80 characters as I think limiting that >> line to 80 characters makes code look bit ugly. But if anyone is having >> issue with that then I am fine with limiting it to 80 chracters. > What about this? > > if (default_hstate_max_huge_pages && !default_hstate.max_huge_pages) > default_hstate.max_huge_pages = default_hstate_max_huge_pages; Yes, it does the same thing. I thought about it. But to me somehow it looks hard to read. So, personally I don't prefer it. Do you want me to change this? >> --- >> mm/hugetlb.c | 6 ++++-- >> 1 file changed, 4 insertions(+), 2 deletions(-) >> >> diff --git a/mm/hugetlb.c b/mm/hugetlb.c >> index 06ae13e..01f2b48 100644 >> --- a/mm/hugetlb.c >> +++ b/mm/hugetlb.c >> @@ -2630,8 +2630,10 @@ static int __init hugetlb_init(void) >> hugetlb_add_hstate(HUGETLB_PAGE_ORDER); >> } >> default_hstate_idx = hstate_index(size_to_hstate(default_hstate_size)); >> - if (default_hstate_max_huge_pages) >> - default_hstate.max_huge_pages = default_hstate_max_huge_pages; >> + if (default_hstate_max_huge_pages) { >> + if (!default_hstate.max_huge_pages) >> + default_hstate.max_huge_pages = default_hstate_max_huge_pages; >> + } >> >> hugetlb_init_hstates(); >> gather_bootmem_prealloc(); >> -- >> 2.1.4 >> >> -- >> 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 -- Vaishali