From: Michal Hocko <mhocko@kernel.org> To: Aaron Lu <aaron.lu@intel.com> Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, Dave Hansen <dave.hansen@intel.com>, Tim Chen <tim.c.chen@intel.com>, Andrew Morton <akpm@linux-foundation.org>, Ying Huang <ying.huang@intel.com> Subject: Re: [PATCH v2 0/5] mm: support parallel free of memory Date: Wed, 15 Mar 2017 17:28:43 +0100 [thread overview] Message-ID: <20170315162843.GA27197@dhcp22.suse.cz> (raw) In-Reply-To: <20170315154406.GF2442@aaronlu.sh.intel.com> On Wed 15-03-17 23:44:07, Aaron Lu wrote: > On Wed, Mar 15, 2017 at 03:18:14PM +0100, Michal Hocko wrote: > > On Wed 15-03-17 16:59:59, Aaron Lu wrote: > > [...] > > > The proposed parallel free did this: if the process has many pages to be > > > freed, accumulate them in these struct mmu_gather_batch(es) one after > > > another till 256K pages are accumulated. Then take this singly linked > > > list starting from tlb->local.next off struct mmu_gather *tlb and free > > > them in a worker thread. The main thread can return to continue zap > > > other pages(after freeing pages pointed by tlb->local.pages). > > > > I didn't have a look at the implementation yet but there are two > > concerns that raise up from this description. Firstly how are we going > > to tune the number of workers. I assume there will be some upper bound > > (one of the patch subject mentions debugfs for tuning) and secondly > > The workers are put in a dedicated workqueue which is introduced in > patch 3/5 and the number of workers can be tuned through that workqueue's > sysfs interface: max_active. I suspect we cannot expect users to tune this. What do you consider a reasonable default? Moreover, and this is a more generic question, is this functionality useful in general purpose workloads? After all the amount of the work to be done is the same we just risk more lock contentions, unexpected CPU usage etc. Which workloads will benefit from having exit path faster? > > if we offload the page freeing to the worker then the original context > > can consume much more cpu cycles than it was configured via cpu I was not precise here. I meant to say more cpu cycles per time unit that it was allowed. > > controller. How are we going to handle that? Or is this considered > > acceptable? > > I'll need to think about and take a look at this subject(not familiar > with cpu controller). the main problem is that kworkers will not belong to the same cpu group and so they will not be throttled properly. -- Michal Hocko SUSE Labs
WARNING: multiple messages have this Message-ID (diff)
From: Michal Hocko <mhocko@kernel.org> To: Aaron Lu <aaron.lu@intel.com> Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, Dave Hansen <dave.hansen@intel.com>, Tim Chen <tim.c.chen@intel.com>, Andrew Morton <akpm@linux-foundation.org>, Ying Huang <ying.huang@intel.com> Subject: Re: [PATCH v2 0/5] mm: support parallel free of memory Date: Wed, 15 Mar 2017 17:28:43 +0100 [thread overview] Message-ID: <20170315162843.GA27197@dhcp22.suse.cz> (raw) In-Reply-To: <20170315154406.GF2442@aaronlu.sh.intel.com> On Wed 15-03-17 23:44:07, Aaron Lu wrote: > On Wed, Mar 15, 2017 at 03:18:14PM +0100, Michal Hocko wrote: > > On Wed 15-03-17 16:59:59, Aaron Lu wrote: > > [...] > > > The proposed parallel free did this: if the process has many pages to be > > > freed, accumulate them in these struct mmu_gather_batch(es) one after > > > another till 256K pages are accumulated. Then take this singly linked > > > list starting from tlb->local.next off struct mmu_gather *tlb and free > > > them in a worker thread. The main thread can return to continue zap > > > other pages(after freeing pages pointed by tlb->local.pages). > > > > I didn't have a look at the implementation yet but there are two > > concerns that raise up from this description. Firstly how are we going > > to tune the number of workers. I assume there will be some upper bound > > (one of the patch subject mentions debugfs for tuning) and secondly > > The workers are put in a dedicated workqueue which is introduced in > patch 3/5 and the number of workers can be tuned through that workqueue's > sysfs interface: max_active. I suspect we cannot expect users to tune this. What do you consider a reasonable default? Moreover, and this is a more generic question, is this functionality useful in general purpose workloads? After all the amount of the work to be done is the same we just risk more lock contentions, unexpected CPU usage etc. Which workloads will benefit from having exit path faster? > > if we offload the page freeing to the worker then the original context > > can consume much more cpu cycles than it was configured via cpu I was not precise here. I meant to say more cpu cycles per time unit that it was allowed. > > controller. How are we going to handle that? Or is this considered > > acceptable? > > I'll need to think about and take a look at this subject(not familiar > with cpu controller). the main problem is that kworkers will not belong to the same cpu group and so they will not be throttled properly. -- Michal Hocko SUSE Labs -- 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:[~2017-03-15 16:28 UTC|newest] Thread overview: 84+ messages / expand[flat|nested] mbox.gz Atom feed top 2017-03-15 8:59 [PATCH v2 0/5] mm: support parallel free of memory Aaron Lu 2017-03-15 8:59 ` Aaron Lu 2017-03-15 9:00 ` [PATCH v2 1/5] mm: add tlb_flush_mmu_free_batches Aaron Lu 2017-03-15 9:00 ` Aaron Lu 2017-03-15 9:00 ` [PATCH v2 2/5] mm: parallel free pages Aaron Lu 2017-03-15 9:00 ` Aaron Lu 2017-03-15 9:42 ` Hillf Danton 2017-03-15 9:42 ` Hillf Danton 2017-03-15 11:54 ` Aaron Lu 2017-03-15 11:54 ` Aaron Lu 2017-03-15 9:00 ` [PATCH v2 3/5] mm: use a dedicated workqueue for the free workers Aaron Lu 2017-03-15 9:00 ` Aaron Lu 2017-03-22 6:33 ` Minchan Kim 2017-03-22 6:33 ` Minchan Kim 2017-03-22 8:41 ` Aaron Lu 2017-03-22 8:41 ` Aaron Lu 2017-03-22 8:55 ` Minchan Kim 2017-03-22 8:55 ` Minchan Kim 2017-03-22 13:43 ` Aaron Lu 2017-03-22 13:43 ` Aaron Lu 2017-03-23 5:53 ` Minchan Kim 2017-03-23 5:53 ` Minchan Kim 2017-03-23 15:38 ` Dave Hansen 2017-03-23 15:38 ` Dave Hansen 2017-03-24 12:37 ` Aaron Lu 2017-03-24 12:37 ` Aaron Lu 2017-03-15 9:00 ` [PATCH v2 4/5] mm: add force_free_pages in zap_pte_range Aaron Lu 2017-03-15 9:00 ` Aaron Lu 2017-03-15 9:00 ` [PATCH v2 5/5] mm: add debugfs interface for parallel free tuning Aaron Lu 2017-03-15 9:00 ` Aaron Lu 2017-03-15 14:18 ` [PATCH v2 0/5] mm: support parallel free of memory Michal Hocko 2017-03-15 14:18 ` Michal Hocko 2017-03-15 15:44 ` Aaron Lu 2017-03-15 15:44 ` Aaron Lu 2017-03-15 16:28 ` Michal Hocko [this message] 2017-03-15 16:28 ` Michal Hocko 2017-03-15 21:38 ` Tim Chen 2017-03-15 21:38 ` Tim Chen 2017-03-16 9:07 ` Michal Hocko 2017-03-16 9:07 ` Michal Hocko 2017-03-16 18:36 ` Tim Chen 2017-03-16 18:36 ` Tim Chen 2017-03-17 7:47 ` Michal Hocko 2017-03-17 7:47 ` Michal Hocko 2017-03-17 8:07 ` Minchan Kim 2017-03-17 8:07 ` Minchan Kim 2017-03-17 12:33 ` Aaron Lu 2017-03-17 12:33 ` Aaron Lu 2017-03-17 12:59 ` Michal Hocko 2017-03-17 12:59 ` Michal Hocko 2017-03-17 13:16 ` Peter Zijlstra 2017-03-17 13:16 ` Peter Zijlstra 2017-03-17 12:53 ` Peter Zijlstra 2017-03-17 12:53 ` Peter Zijlstra 2017-03-17 13:05 ` Michal Hocko 2017-03-17 13:05 ` Michal Hocko 2017-03-21 14:54 ` Dave Hansen 2017-03-21 14:54 ` Dave Hansen 2017-03-22 8:02 ` Aaron Lu 2017-03-22 8:02 ` Aaron Lu 2017-03-24 7:04 ` Aaron Lu 2017-03-24 7:04 ` Aaron Lu 2017-03-21 15:18 ` Tim Chen 2017-03-21 15:18 ` Tim Chen 2017-03-16 6:54 ` Aaron Lu 2017-03-16 6:54 ` Aaron Lu 2017-03-16 7:34 ` Aaron Lu 2017-03-16 7:34 ` Aaron Lu 2017-03-16 13:51 ` Aaron Lu 2017-03-16 13:51 ` Aaron Lu 2017-03-16 14:14 ` Aaron Lu 2017-03-16 14:14 ` Aaron Lu 2017-03-15 14:56 ` Vlastimil Babka 2017-03-15 14:56 ` Vlastimil Babka 2017-03-15 15:50 ` Aaron Lu 2017-03-15 15:50 ` Aaron Lu 2017-03-17 3:10 ` Aaron Lu 2017-03-17 3:10 ` Aaron Lu 2017-03-16 19:38 ` Alex Thorlton 2017-03-16 19:38 ` Alex Thorlton 2017-03-17 2:21 ` Aaron Lu 2017-03-17 2:21 ` Aaron Lu 2017-03-20 19:15 ` Alex Thorlton 2017-03-20 19:15 ` Alex Thorlton
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