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Tue, 03 Sep 2019 21:26:12 +0000 Received: from pps.filterd (aserp3020.oracle.com [127.0.0.1]) by aserp3020.oracle.com (8.16.0.27/8.16.0.27) with SMTP id x83LNoLh142829; Tue, 3 Sep 2019 21:26:11 GMT Received: from userv0122.oracle.com (userv0122.oracle.com [156.151.31.75]) by aserp3020.oracle.com with ESMTP id 2us5phbbrb-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Tue, 03 Sep 2019 21:26:11 +0000 Received: from abhmp0006.oracle.com (abhmp0006.oracle.com [141.146.116.12]) by userv0122.oracle.com (8.14.4/8.14.4) with ESMTP id x83LQ9PT028518; Tue, 3 Sep 2019 21:26:09 GMT Received: from [192.168.1.222] (/71.63.128.209) by default (Oracle Beehive Gateway v4.0) with ESMTP ; Tue, 03 Sep 2019 14:26:09 -0700 Subject: Re: [PATCH v2] mm/hugetlb: avoid looping to the same hugepage if !pages and !vmas To: Zhigang Lu , luzhigang001@gmail.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org Cc: Zhigang Lu References: <1567086657-22528-1-git-send-email-totty.lu@gmail.com> From: Mike Kravetz Message-ID: <1f0e6e1a-c947-f389-801e-b1d748cb5bce@oracle.com> Date: Tue, 3 Sep 2019 14:26:08 -0700 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.7.0 MIME-Version: 1.0 In-Reply-To: <1567086657-22528-1-git-send-email-totty.lu@gmail.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit X-Proofpoint-Virus-Version: vendor=nai engine=6000 definitions=9369 signatures=668685 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 suspectscore=0 malwarescore=0 phishscore=0 bulkscore=0 spamscore=0 mlxscore=0 mlxlogscore=999 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1906280000 definitions=main-1909030214 X-Proofpoint-Virus-Version: vendor=nai engine=6000 definitions=9369 signatures=668685 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 priorityscore=1501 malwarescore=0 suspectscore=0 phishscore=0 bulkscore=0 spamscore=0 clxscore=1011 lowpriorityscore=0 mlxscore=0 impostorscore=0 mlxlogscore=999 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1906280000 definitions=main-1909030214 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On 8/29/19 6:50 AM, Zhigang Lu wrote: > From: Zhigang Lu > > When mmapping an existing hugetlbfs file with MAP_POPULATE, we find > it is very time consuming. For example, mmapping a 128GB file takes > about 50 milliseconds. Sampling with perfevent shows it spends 99% > time in the same_page loop in follow_hugetlb_page(). > > samples: 205 of event 'cycles', Event count (approx.): 136686374 > - 99.04% test_mmap_huget [kernel.kallsyms] [k] follow_hugetlb_page > follow_hugetlb_page > __get_user_pages > __mlock_vma_pages_range > __mm_populate > vm_mmap_pgoff > sys_mmap_pgoff > sys_mmap > system_call_fastpath > __mmap64 > > follow_hugetlb_page() is called with pages=NULL and vmas=NULL, so for > each hugepage, we run into the same_page loop for pages_per_huge_page() > times, but doing nothing. With this change, it takes less then 1 > millisecond to mmap a 128GB file in hugetlbfs. Thanks for the analysis! Just curious, do you have an application that does this (mmap(MAP_POPULATE) for an existing hugetlbfs file), or was this part of some test suite or debug code? > Signed-off-by: Zhigang Lu > Reviewed-by: Haozhong Zhang > Reviewed-by: Zongming Zhang > Acked-by: Matthew Wilcox > --- > mm/hugetlb.c | 11 +++++++++++ > 1 file changed, 11 insertions(+) > > diff --git a/mm/hugetlb.c b/mm/hugetlb.c > index 6d7296d..2df941a 100644 > --- a/mm/hugetlb.c > +++ b/mm/hugetlb.c > @@ -4391,6 +4391,17 @@ long follow_hugetlb_page(struct mm_struct *mm, struct vm_area_struct *vma, > break; > } > } It might be helpful to add a comment here to help readers of the code. Something like: /* * If subpage information not requested, update counters * and skip the same_page loop below. */ > + > + if (!pages && !vmas && !pfn_offset && > + (vaddr + huge_page_size(h) < vma->vm_end) && > + (remainder >= pages_per_huge_page(h))) { > + vaddr += huge_page_size(h); > + remainder -= pages_per_huge_page(h); > + i += pages_per_huge_page(h); > + spin_unlock(ptl); > + continue; > + } > + > same_page: > if (pages) { > pages[i] = mem_map_offset(page, pfn_offset); > With a comment added to the code, Reviewed-by: Mike Kravetz -- Mike Kravetz