From: Anshuman Khandual <khandual@linux.vnet.ibm.com> To: Michal Hocko <mhocko@kernel.org>, Anshuman Khandual <khandual@linux.vnet.ibm.com> Cc: Xishi Qiu <qiuxishi@huawei.com>, Andrew Morton <akpm@linux-foundation.org>, KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>, Reza Arbab <arbab@linux.vnet.ibm.com>, Yasuaki Ishimatsu <yasu.isimatu@gmail.com>, Igor Mammedov <imammedo@redhat.com>, Vitaly Kuznetsov <vkuznets@redhat.com>, linux-mm@kvack.org, LKML <linux-kernel@vger.kernel.org> Subject: Re: [PATCH 2/2] mm, memory_hotplug: remove timeout from __offline_memory Date: Tue, 5 Sep 2017 14:24:26 +0530 [thread overview] Message-ID: <9a43dffa-0e0a-ed53-63a2-677cd162a1a7@linux.vnet.ibm.com> (raw) In-Reply-To: <20170905072310.6iuui7h7rwrrnxdy@dhcp22.suse.cz> On 09/05/2017 12:53 PM, Michal Hocko wrote: > On Tue 05-09-17 11:16:57, Anshuman Khandual wrote: >> On 09/04/2017 02:45 PM, Michal Hocko wrote: >>> On Mon 04-09-17 17:05:15, Xishi Qiu wrote: >>>> On 2017/9/4 17:01, Michal Hocko wrote: >>>> >>>>> On Mon 04-09-17 16:58:30, Xishi Qiu wrote: >>>>>> On 2017/9/4 16:21, Michal Hocko wrote: >>>>>> >>>>>>> From: Michal Hocko <mhocko@suse.com> >>>>>>> >>>>>>> We have a hardcoded 120s timeout after which the memory offline fails >>>>>>> basically since the hot remove has been introduced. This is essentially >>>>>>> a policy implemented in the kernel. Moreover there is no way to adjust >>>>>>> the timeout and so we are sometimes facing memory offline failures if >>>>>>> the system is under a heavy memory pressure or very intensive CPU >>>>>>> workload on large machines. >>>>>>> >>>>>>> It is not very clear what purpose the timeout actually serves. The >>>>>>> offline operation is interruptible by a signal so if userspace wants >>>>>> Hi Michal, >>>>>> >>>>>> If the user know what he should do if migration for a long time, >>>>>> it is OK, but I don't think all the users know this operation >>>>>> (e.g. ctrl + c) and the affect. >>>>> How is this operation any different from other potentially long >>>>> interruptible syscalls? >>>>> >>>> Hi Michal, >>>> >>>> I means the user should stop it by himself if migration always retry in endless. >>> If the memory is migrateable then the migration should finish >>> eventually. It can take some time but it shouldn't be an endless loop. >> >> But what if some how the temporary condition (page removed from the PCP >> LRU list and has not been freed yet to the buddy) happens again and again. > > How would that happen? We have all pages in the range MIGRATE_ISOLATE so > no pages will get reallocated and we know that there are no unmigratable > pages in the range. So we only should have temporary failures for > migration. If that is not the case then we have a bug somewhere. Right. > >> I understand we have schedule() and yield() to make sure that the context >> does not hold the CPU for ever but it can take theoretically very long >> time if not endless to finish. In that case sending signal to the user > > I guess you meant to say signal from the user space... Yes. > >> space process who initiated the offline request is the only way to stop >> this retry loop. I think this is still a better approach than the 120 >> second timeout which was kind of arbitrary. > > Yeah the context is interruptible so if the operation takes unbearably > too long then a watchdog can be setup trivially and to the user defined > value. There is a good reason we do not add hardocded timeouts to the > kernel. > Right.
WARNING: multiple messages have this Message-ID (diff)
From: Anshuman Khandual <khandual@linux.vnet.ibm.com> To: Michal Hocko <mhocko@kernel.org>, Anshuman Khandual <khandual@linux.vnet.ibm.com> Cc: Xishi Qiu <qiuxishi@huawei.com>, Andrew Morton <akpm@linux-foundation.org>, KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>, Reza Arbab <arbab@linux.vnet.ibm.com>, Yasuaki Ishimatsu <yasu.isimatu@gmail.com>, Igor Mammedov <imammedo@redhat.com>, Vitaly Kuznetsov <vkuznets@redhat.com>, linux-mm@kvack.org, LKML <linux-kernel@vger.kernel.org> Subject: Re: [PATCH 2/2] mm, memory_hotplug: remove timeout from __offline_memory Date: Tue, 5 Sep 2017 14:24:26 +0530 [thread overview] Message-ID: <9a43dffa-0e0a-ed53-63a2-677cd162a1a7@linux.vnet.ibm.com> (raw) In-Reply-To: <20170905072310.6iuui7h7rwrrnxdy@dhcp22.suse.cz> On 09/05/2017 12:53 PM, Michal Hocko wrote: > On Tue 05-09-17 11:16:57, Anshuman Khandual wrote: >> On 09/04/2017 02:45 PM, Michal Hocko wrote: >>> On Mon 04-09-17 17:05:15, Xishi Qiu wrote: >>>> On 2017/9/4 17:01, Michal Hocko wrote: >>>> >>>>> On Mon 04-09-17 16:58:30, Xishi Qiu wrote: >>>>>> On 2017/9/4 16:21, Michal Hocko wrote: >>>>>> >>>>>>> From: Michal Hocko <mhocko@suse.com> >>>>>>> >>>>>>> We have a hardcoded 120s timeout after which the memory offline fails >>>>>>> basically since the hot remove has been introduced. This is essentially >>>>>>> a policy implemented in the kernel. Moreover there is no way to adjust >>>>>>> the timeout and so we are sometimes facing memory offline failures if >>>>>>> the system is under a heavy memory pressure or very intensive CPU >>>>>>> workload on large machines. >>>>>>> >>>>>>> It is not very clear what purpose the timeout actually serves. The >>>>>>> offline operation is interruptible by a signal so if userspace wants >>>>>> Hi Michal, >>>>>> >>>>>> If the user know what he should do if migration for a long time, >>>>>> it is OK, but I don't think all the users know this operation >>>>>> (e.g. ctrl + c) and the affect. >>>>> How is this operation any different from other potentially long >>>>> interruptible syscalls? >>>>> >>>> Hi Michal, >>>> >>>> I means the user should stop it by himself if migration always retry in endless. >>> If the memory is migrateable then the migration should finish >>> eventually. It can take some time but it shouldn't be an endless loop. >> >> But what if some how the temporary condition (page removed from the PCP >> LRU list and has not been freed yet to the buddy) happens again and again. > > How would that happen? We have all pages in the range MIGRATE_ISOLATE so > no pages will get reallocated and we know that there are no unmigratable > pages in the range. So we only should have temporary failures for > migration. If that is not the case then we have a bug somewhere. Right. > >> I understand we have schedule() and yield() to make sure that the context >> does not hold the CPU for ever but it can take theoretically very long >> time if not endless to finish. In that case sending signal to the user > > I guess you meant to say signal from the user space... Yes. > >> space process who initiated the offline request is the only way to stop >> this retry loop. I think this is still a better approach than the 120 >> second timeout which was kind of arbitrary. > > Yeah the context is interruptible so if the operation takes unbearably > too long then a watchdog can be setup trivially and to the user defined > value. There is a good reason we do not add hardocded timeouts to the > kernel. > Right. -- 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: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>
next prev parent reply other threads:[~2017-09-05 8:54 UTC|newest] Thread overview: 42+ messages / expand[flat|nested] mbox.gz Atom feed top 2017-09-04 8:21 [PATCH 0/2] mm, memory_hotplug: redefine memory offline retry logic Michal Hocko 2017-09-04 8:21 ` Michal Hocko 2017-09-04 8:21 ` [PATCH 1/2] mm, memory_hotplug: do not fail offlining too early Michal Hocko 2017-09-04 8:21 ` Michal Hocko 2017-09-05 6:29 ` Anshuman Khandual 2017-09-05 6:29 ` Anshuman Khandual 2017-09-05 7:13 ` Michal Hocko 2017-09-05 7:13 ` Michal Hocko 2017-09-08 17:26 ` Vlastimil Babka 2017-09-08 17:26 ` Vlastimil Babka 2017-09-11 8:17 ` Michal Hocko 2017-09-11 8:17 ` Michal Hocko 2017-09-13 11:41 ` Vlastimil Babka 2017-09-13 11:41 ` Vlastimil Babka 2017-09-13 12:10 ` Michal Hocko 2017-09-13 12:10 ` Michal Hocko 2017-09-13 12:14 ` Michal Hocko 2017-09-13 12:14 ` Michal Hocko 2017-09-13 12:19 ` Vlastimil Babka 2017-09-13 12:19 ` Vlastimil Babka 2017-09-13 12:32 ` Michal Hocko 2017-09-13 12:32 ` Michal Hocko 2017-09-04 8:21 ` [PATCH 2/2] mm, memory_hotplug: remove timeout from __offline_memory Michal Hocko 2017-09-04 8:21 ` Michal Hocko 2017-09-04 8:58 ` Xishi Qiu 2017-09-04 8:58 ` Xishi Qiu 2017-09-04 9:01 ` Michal Hocko 2017-09-04 9:01 ` Michal Hocko 2017-09-04 9:05 ` Xishi Qiu 2017-09-04 9:05 ` Xishi Qiu 2017-09-04 9:15 ` Michal Hocko 2017-09-04 9:15 ` Michal Hocko 2017-09-05 5:46 ` Anshuman Khandual 2017-09-05 5:46 ` Anshuman Khandual 2017-09-05 7:23 ` Michal Hocko 2017-09-05 7:23 ` Michal Hocko 2017-09-05 8:54 ` Anshuman Khandual [this message] 2017-09-05 8:54 ` Anshuman Khandual 2017-09-08 17:27 ` Vlastimil Babka 2017-09-08 17:27 ` Vlastimil Babka 2017-09-18 7:08 [PATCH v2 0/2] mm, memory_hotplug: redefine memory offline retry logic Michal Hocko 2017-09-18 7:08 ` [PATCH 2/2] mm, memory_hotplug: remove timeout from __offline_memory Michal Hocko 2017-09-18 7:08 ` Michal Hocko
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