From mboxrd@z Thu Jan 1 00:00:00 1970 From: Michal Hocko Subject: Re: [PATCH V4] mlx4_core: allocate ICM memory in page size chunks Date: Mon, 4 Jun 2018 08:27:37 +0200 Message-ID: <20180604062737.GA19202@dhcp22.suse.cz> References: <7a353b65-6b7f-1aee-1c48-e83c8e02f693@gmail.com> <0e11e0fc-6ccf-aa93-9c4f-b9eae1b90643@gmail.com> <20180531065405.GH15278@dhcp22.suse.cz> <20180531085532.GK15278@dhcp22.suse.cz> <20180531091022.GL15278@dhcp22.suse.cz> <7d8f52e1-aa16-d20c-a9a8-35ad88c0b1ab@oracle.com> <20180601073137.GV15278@dhcp22.suse.cz> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: Sender: linux-kernel-owner@vger.kernel.org To: Qing Huang Cc: Eric Dumazet , David Miller , tariqt@mellanox.com, haakon.bugge@oracle.com, yanjun.zhu@oracle.com, netdev@vger.kernel.org, linux-rdma@vger.kernel.org, linux-kernel@vger.kernel.org, gi-oh.kim@profitbricks.com, "santosh.shilimkar@oracle.com" , Vlastimil Babka List-Id: linux-rdma@vger.kernel.org On Fri 01-06-18 15:05:26, Qing Huang wrote: > > > On 6/1/2018 12:31 AM, Michal Hocko wrote: > > On Thu 31-05-18 19:04:46, Qing Huang wrote: > > > > > > On 5/31/2018 2:10 AM, Michal Hocko wrote: > > > > On Thu 31-05-18 10:55:32, Michal Hocko wrote: > > > > > On Thu 31-05-18 04:35:31, Eric Dumazet wrote: > > > > [...] > > > > > > I merely copied/pasted from alloc_skb_with_frags() :/ > > > > > I will have a look at it. Thanks! > > > > OK, so this is an example of an incremental development ;). > > > > > > > > __GFP_NORETRY was added by ed98df3361f0 ("net: use __GFP_NORETRY for > > > > high order allocations") to prevent from OOM killer. Yet this was > > > > not enough because fb05e7a89f50 ("net: don't wait for order-3 page > > > > allocation") didn't want an excessive reclaim for non-costly orders > > > > so it made it completely NOWAIT while it preserved __GFP_NORETRY in > > > > place which is now redundant. Should I send a patch? > > > > > > > Just curious, how about GFP_ATOMIC flag? Would it work in a similar fashion? > > > We experimented > > > with it a bit in the past but it seemed to cause other issue in our tests. > > > :-) > > GFP_ATOMIC is a non-sleeping (aka no reclaim) context with an access to > > memory reserves. So the risk is that you deplete those reserves and > > cause issues to other subsystems which need them as well. > > > > > By the way, we didn't encounter any OOM killer events. It seemed that the > > > mlx4_alloc_icm() triggered slowpath. > > > We still had about 2GB free memory while it was highly fragmented. > > The compaction was able to make a reasonable forward progress for you. > > But considering mlx4_alloc_icm is called with GFP_KERNEL resp. GFP_HIGHUSER > > then the OOM killer is clearly possible as long as the order is lower > > than 4. > > The allocation was 256KB so the order was much higher than 4. The compaction > seemed to be the root > cause for our problem. It took too long to finish its work while putting > mlx4_alloc_icm to sleep in a heavily > fragmented memory situation . Will NORETRY flag avoid the compaction ops and > fail the 256KB allocation > immediately so mlx4_alloc_icm can enter adjustable lower order allocation > code path quickly? Costly orders should only perform a light compaction attempt unless __GFP_RETRY_MAY_FAIL is used IIRC. CCing Vlastimil. So __GFP_NORETRY shouldn't make any difference. -- Michal Hocko SUSE Labs