From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pf0-f197.google.com (mail-pf0-f197.google.com [209.85.192.197]) by kanga.kvack.org (Postfix) with ESMTP id 6A5ED6B0003 for ; Thu, 8 Mar 2018 01:51:27 -0500 (EST) Received: by mail-pf0-f197.google.com with SMTP id v3so2522550pfm.21 for ; Wed, 07 Mar 2018 22:51:27 -0800 (PST) Received: from smtp.codeaurora.org (smtp.codeaurora.org. [198.145.29.96]) by mx.google.com with ESMTPS id y7-v6si5554653plk.353.2018.03.07.22.51.26 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 07 Mar 2018 22:51:26 -0800 (PST) Subject: Re: [PATCH] slub: Fix misleading 'age' in verbose slub prints References: <1520423266-28830-1-git-send-email-cpandya@codeaurora.org> <20180307182212.GA23411@bombadil.infradead.org> From: Chintan Pandya Message-ID: Date: Thu, 8 Mar 2018 12:21:19 +0530 MIME-Version: 1.0 In-Reply-To: <20180307182212.GA23411@bombadil.infradead.org> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Matthew Wilcox , Christopher Lameter Cc: penberg@kernel.org, rientjes@google.com, iamjoonsoo.kim@lge.com, akpm@linux-foundation.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org On 3/7/2018 11:52 PM, Matthew Wilcox wrote: > On Wed, Mar 07, 2018 at 12:13:56PM -0600, Christopher Lameter wrote: >> On Wed, 7 Mar 2018, Chintan Pandya wrote: >>> In this case, object got freed later but 'age' shows >>> otherwise. This could be because, while printing >>> this info, we print allocation traces first and >>> free traces thereafter. In between, if we get schedule >>> out, (jiffies - t->when) could become meaningless. >> >> Ok then get the jiffies earlier? >> >>> So, simply print when the object was allocated/freed. >> >> The tick value may not related to anything in the logs that is why the >> "age" is there. How do I know how long ago the allocation was if I look at >> the log and only see long and large number of ticks since bootup? > > I missed that the first read-through too. The trick is that there are two printks: > > [ 6044.170804] INFO: Allocated in binder_transaction+0x4b0/0x2448 age=731 cpu=3 pid=5314 > ... > [ 6044.216696] INFO: Freed in binder_free_transaction+0x2c/0x58 age=735 cpu=6 pid=2079 > > If you print the raw value, then you can do the subtraction yourself; > if you've subtracted it from jiffies each time, you've at least introduced > jitter, and possibly enough jitter to confuse and mislead. > This is exactly what I was thinking. But looking up 'age' is easy compared to 'when' and this seems required as from Christopher's reply. So, will raise new patch cleaning commit message a bit. Chintan -- Qualcomm India Private Limited, on behalf of Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum, a Linux Foundation Collaborative Project