From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: DKIM-Filter: OpenDKIM Filter v2.10.3 mail.efficios.com 0B37A1CAAC1 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=efficios.com; s=default; t=1553016875; bh=/8CBk1am8WoG2uZKCO58bIGV21nb86z8tzPqXUImc+4=; h=Date:From:To:Message-ID:MIME-Version; b=gwYPEonTloILKq/XMRP/GbRGR7kjYjfYgJSI3n0UkLlnVYPf9PcDf8OM+S1K2+OvT ndh4nATV4ak2sMql6XZICRh2BKsHkaIhEoQdH3/J6g8dMEVH2brCYe7JXZbEYmIhGl 622d7e1L25afLmxmXXbhP8RtHS9iK6rGQ8iyme/vteIzvWXBNTPfL70/bdtuMA+BOS lcYx0cKy6u6uj5+vpj4lSMt76tMkVwp+rRBpt1XjKduX3z+Gsa8BGQKEUzWFhiUK6s xFav/itfSZhoLQYRK5OQNsrQGN1pserm3IB/Rnvi/CeaZtDH56gdBMgGqrOOb5KTLZ g7crOm5XMOaIQ== Date: Tue, 19 Mar 2019 13:34:34 -0400 (EDT) From: Mathieu Desnoyers Message-ID: <1199524058.2398.1553016874435.JavaMail.zimbra@efficios.com> In-Reply-To: References: <60988959.4070.1541112982406.JavaMail.zimbra@efficios.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Subject: Re: [diamon-discuss] [RELEASE] LTTng-modules 2.9.11, 2.10.8, 2.11.0-rc2 (Linux kernel tracer) List-Id: DiaMon diagnostic and monitoring workgroup general discussions List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Joel Fernandes Cc: diamon-discuss@lists.linuxfoundation.org, lttng-dev , linux-kernel ----- On Nov 1, 2018, at 7:33 PM, Joel Fernandes via diamon-discuss diamon-discuss@lists.linuxfoundation.org wrote: > On Thu, Nov 1, 2018 at 3:56 PM Mathieu Desnoyers > wrote: >> >> Hi, >> >> This is a set of bugfix releases of the LTTng modules kernel tracer. >> It covers the three currently active lttng-modules branches: the >> 2.9 and 2.10 stable branches, as well as the 2.11 branch in release >> candidate cycle. >> >> Those releases add support for kernel 4.19. >> >> One important improvement is to prevent allocation of buffers larger >> than the available memory, which can cause the OOM killer to trigger. >> Even if the OOM killer end up having to trigger, the current OOM kill >> target is set to the current thread while allocating buffers. > > This is interesting. Me and Steve were looking at exactly this issue > with the ftrace ring buffer a few months ago. Turns out that even > setting the OOM kill target may not be enough to prevent all OOMs. I > don't remember the reason why not, I'll have to dig out those threads > but that's what the -mm folks said at the time. I did remember vaguely > that I tested it and the kill target doesn't always get killed.. its > possible that something *other* parallel allocation can be victimized > AFAIR, even though the culprit is the kill target. > Hi Joel, Sorry for the late reply. Thanks for your input! Here is a description of the solution we implemented: " Get an estimate of the number of available pages and return ENOMEM if there are not enough pages to cover the needs of the caller. Also, mark the calling user thread as the first target for the OOM killer in case the estimate of available pages was wrong. This greatly reduces the attack surface of this issue as well as reducing its potential impact. This approach is inspired by the one taken by the Linux kernel trace ring buffer[1]." This is implemented in commit 1f0ab1eb040 "Prevent allocation of buffers if exceeding available memory" within lttng-modules. Are you aware of another way to achieve this that would prevent the incorrect OOM victimization scenario you describe above ? Thanks, Mathieu -- Mathieu Desnoyers EfficiOS Inc. http://www.efficios.com