From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-ed1-f71.google.com (mail-ed1-f71.google.com [209.85.208.71]) by kanga.kvack.org (Postfix) with ESMTP id 436728E0002 for ; Thu, 20 Dec 2018 11:03:17 -0500 (EST) Received: by mail-ed1-f71.google.com with SMTP id e29so2785293ede.19 for ; Thu, 20 Dec 2018 08:03:17 -0800 (PST) Received: from mx0a-001b2d01.pphosted.com (mx0b-001b2d01.pphosted.com. [148.163.158.5]) by mx.google.com with ESMTPS id z7-v6si1600399eji.249.2018.12.20.08.03.15 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Thu, 20 Dec 2018 08:03:15 -0800 (PST) Received: from pps.filterd (m0098416.ppops.net [127.0.0.1]) by mx0b-001b2d01.pphosted.com (8.16.0.22/8.16.0.22) with SMTP id wBKG06vV004853 for ; Thu, 20 Dec 2018 11:03:14 -0500 Received: from e17.ny.us.ibm.com (e17.ny.us.ibm.com [129.33.205.207]) by mx0b-001b2d01.pphosted.com with ESMTP id 2pgdqf1npk-1 (version=TLSv1.2 cipher=AES256-GCM-SHA384 bits=256 verify=NOT) for ; Thu, 20 Dec 2018 11:03:14 -0500 Received: from localhost by e17.ny.us.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Thu, 20 Dec 2018 16:03:13 -0000 Date: Thu, 20 Dec 2018 08:03:13 -0800 From: "Paul E. McKenney" Subject: Re: Ipmi modules and linux-4.19.1 Reply-To: paulmck@linux.ibm.com References: <20181220154217.GB2509588@devbig004.ftw2.facebook.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20181220154217.GB2509588@devbig004.ftw2.facebook.com> Message-Id: <20181220160313.GB4170@linux.ibm.com> Sender: owner-linux-mm@kvack.org List-ID: To: Tejun Heo Cc: Angel Shtilianov , linux-mm@kvack.org, dennis@kernel.org, cl@linux.com, jeyu@kernel.org On Thu, Dec 20, 2018 at 07:42:17AM -0800, Tejun Heo wrote: > Hello, Angel. > > (cc'ing Paul for SRCU) > > On Thu, Dec 20, 2018 at 09:55:10AM +0200, Angel Shtilianov wrote: > > Hi everybody. > > A couple of days I've decided to migrate several servers on > > linux-4.19. What I've observed is that I have no /dev/ipmi. After > > taking a look into the boot log I've found that ipmi modules are > > complaining about percpu memory allocation failures: > > https://pastebin.com/MCDssZzV > ... > > -#define PERCPU_DYNAMIC_RESERVE (28 << 10) > > +#define PERCPU_DYNAMIC_RESERVE (28 << 11) > > So, you prolly just needed to bump this number. The reserved percpu > area is used to accommodate static percpu variables used by modules. > They are special because code generation assumes static symbols aren't > too far from the program counter. The usual dynamic percpu area is > way high up in vmalloc area, so if we put static percpu allocations > there, they go out of range for module symbol relocations. > > The reserved area has some issues. > > 1. The area is not dynamically mapped, meaning that however much we > reserve is hard allocated on boot for future module uses, so we > don't can't increase it willy-nilly. > > 2. There is no mechanism to adjust the size dynamically. 28k is just > a number I pulled out of my ass after looking at some common > configs like a decade ago, so it being low now isn't too > surprising. Provided that we can't make it run-time dynamic (and I > can't think of a way to do that), the right thing to do would be > sizing it during build with some buffer and allow it to be > overridden boot time. This is definitely doable. > > BTW, ipmi's extra usage, 8k, is coming from the use of static SRCU. > Paul, that's quite a bit of percpu memory to reserve statically. > Would it be possible to make srcu_struct init dynamic so that it can > use the normal percpu_alloc? That way, this problem can be completely > side-stepped and it only occupies percpu memory which tends to be > pretty expensive unless ipmi is actually initialized. Yes, it is possible. Just do something like this: struct srcu_struct my_srcu_struct; And before the first use of my_srcu_struct, do this: init_srcu_struct(&my_srcu_struct); This will result in alloc_percpu() being invoked to allocate the needed per-CPU space. If my_srcu_struct is used in a module or some such, then to avoid memory leaks, after the last use of my_srcu_struct, do this: cleanup_srcu_struct(&my_srcu_struct); There are several places in the kernel that take this approach. Thanx, Paul