From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Burakov, Anatoly" Subject: Re: =?utf-8?b?5Zue5aSN77yaIEFib3V0IHRoZSBzaGFyZWQgZmxvY2sg?= =?utf-8?q?for_hugepage_files?= Date: Tue, 19 Sep 2017 15:05:47 +0100 Message-ID: References: Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 8bit Cc: jim@netgate.com To: 912873551@qq.com, dev@dpdk.org Return-path: Received: from mga04.intel.com (mga04.intel.com [192.55.52.120]) by dpdk.org (Postfix) with ESMTP id A1D8E1B1A4 for ; Tue, 19 Sep 2017 16:05:50 +0200 (CEST) In-Reply-To: Content-Language: en-US List-Id: DPDK patches and discussions List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: dev-bounces@dpdk.org Sender: "dev" Hi Bakari, On 12-Sep-17 4:41 AM, 912873551 at qq.com (白长敏) wrote: > Hi Jim, > > > Thank you for reply, i understand it, but i still have two doubts. > > > 1) if i have > 1 DPDK application on a machine, i can use the parameter "--file-prefix" to distinguish, it can work even if have not flock. That's not entirely correct. DPDK will attempt to clean up *all* hugepage files it encounters, not just those that are designated as "its own" via the --file-prefix [1]. This is because hugepages are not freed back to the OS unless its backing file in hugetlbfs is removed from the system, so DPDK needs to clear out any pre-existing hugepage files in order to successfully allocate any hugepages for its use. > 2) If I understand correctly, in the "map_all_hugepages()", after making the shared flock, close(fd), that is to free the flock. Then, in the "clear_hugedir()", it equal to have not flock ? You are correct that normally, closing the file descriptor would release the lock. However, we're also doing an mmap() call on that fd [2], which duplicates the descriptor, and therefore we continue to hold a lock to that file. Quote from mmap() man page [3]: "The mmap() function shall add an extra reference to the file associated with the file descriptor fildes which is not removed by a subsequent close() on that file descriptor. This reference shall be removed when there are no more mappings to the file." [1] http://www.dpdk.org/browse/dpdk/tree/lib/librte_eal/linuxapp/eal/eal_hugepage_info.c#n192 [2] http://www.dpdk.org/browse/dpdk/tree/lib/librte_eal/linuxapp/eal/eal_memory.c#n505 [3] https://linux.die.net/man/3/mmap > > > ------------------ ???? ------------------ > ???: "Jim Thompson";; > ????: 2017?9?12?(???) ??11:10 > ???: "???"<912873551 at qq.com>; > ??: "dev"; > ??: Re: [dpdk-dev] About the shared flock for hugepage files > > > > > Bakari, > > > This is so you can have > 1 DPDK application on a machine and they won't use each other's hugepages. > > > See, for example the comments in clear_hugedir() > > > http://dpdk.org/browse/dpdk/tree/lib/librte_eal/linuxapp/eal/eal_hugepage_info.c#n198 > > > Jim > > On Sep 11, 2017, at 9:16 PM, ??? <912873551 at qq.com> wrote: > > > Hi, everyone, > > > I'm a developer from china, now i have a problem is about the shared flock for hugepage files in the function of "map_all_hugepages()". > > > as follows: > --------------------------------------------------------------------------------------------------- > /* set shared flock on the file. */ > > > if (flock(fd, LOCK_SH | LOCK_NB) == -1) { > > > RTE_LOG(DEBUG, EAL, "%s(): Locking file failed:%s \n", __func__, strerror(errno)); > > > close(fd); > > > return i; > > > } > > > close(fd); > > -------------------------------------------------------------------------------------------------- > there, it gives a shared flock to each hugepage file in /mnt/huge, and close it right away. > > > it makes me puzzled. Why? What doing that is for? > > > I'm looking forward to your reply, thank you very much. > > > best regards, > Bakari. > -- Thanks, Anatoly