From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752131AbdAYRo5 (ORCPT ); Wed, 25 Jan 2017 12:44:57 -0500 Received: from mail-wm0-f68.google.com ([74.125.82.68]:36714 "EHLO mail-wm0-f68.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752055AbdAYRoz (ORCPT ); Wed, 25 Jan 2017 12:44:55 -0500 Date: Wed, 25 Jan 2017 20:44:52 +0300 From: "Kirill A. Shutemov" To: Srikar Dronamraju Cc: Andrew Morton , "Kirill A. Shutemov" , Andrea Arcangeli , Hugh Dickins , Rik van Riel , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Oleg Nesterov , Peter Zijlstra Subject: Re: [PATCH 01/12] uprobes: split THPs before trying replace them Message-ID: <20170125174452.GA4157@node> References: <20170124162824.91275-1-kirill.shutemov@linux.intel.com> <20170124162824.91275-2-kirill.shutemov@linux.intel.com> <20170124132849.73135e8c6e9572be00dbbe79@linux-foundation.org> <20170124222217.GB19920@node.shutemov.name> <20170125165522.GA11569@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20170125165522.GA11569@linux.vnet.ibm.com> User-Agent: Mutt/1.5.23.1 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Jan 25, 2017 at 08:55:22AM -0800, Srikar Dronamraju wrote: > > > > > > > For THPs page_check_address() always fails. It's better to split them > > > > first before trying to replace. > > > > > > So what does this mean. uprobes simply fails to work when trying to > > > place a probe into a THP memory region? > > > > Looks like we can end up with endless retry loop in uprobe_write_opcode(). > > > > > How come nobody noticed (and reported) this when using the feature? > > > > I guess it's not often used for anon memory. > > > > The first time the breakpoint is hit on a page, it replaces the text > page with anon page. Now lets assume we insert breakpoints in all the > pages in a range. Here each page is individually replaced by a non THP > anonpage. (since we dont have bulk breakpoint insertion support, > breakpoint insertion happens one at a time). Now the only interesting > case may be when each of these replaced pages happen to be physically > contiguous so that THP kicks in to replace all of these pages with one > THP page. Can happen in practice? The problem is with the page you try to replace, not with page that you replace it with. > Are there any other cases that I have missed? The binary on tmpfs with huge pages. I wrote test-case that triggers the problem. -- Kirill A. Shutemov From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wm0-f72.google.com (mail-wm0-f72.google.com [74.125.82.72]) by kanga.kvack.org (Postfix) with ESMTP id D25996B0253 for ; Wed, 25 Jan 2017 12:44:55 -0500 (EST) Received: by mail-wm0-f72.google.com with SMTP id r144so39790510wme.0 for ; Wed, 25 Jan 2017 09:44:55 -0800 (PST) Received: from mail-wm0-x242.google.com (mail-wm0-x242.google.com. [2a00:1450:400c:c09::242]) by mx.google.com with ESMTPS id b27si13304889wmi.98.2017.01.25.09.44.54 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 25 Jan 2017 09:44:54 -0800 (PST) Received: by mail-wm0-x242.google.com with SMTP id r144so44107558wme.0 for ; Wed, 25 Jan 2017 09:44:54 -0800 (PST) Date: Wed, 25 Jan 2017 20:44:52 +0300 From: "Kirill A. Shutemov" Subject: Re: [PATCH 01/12] uprobes: split THPs before trying replace them Message-ID: <20170125174452.GA4157@node> References: <20170124162824.91275-1-kirill.shutemov@linux.intel.com> <20170124162824.91275-2-kirill.shutemov@linux.intel.com> <20170124132849.73135e8c6e9572be00dbbe79@linux-foundation.org> <20170124222217.GB19920@node.shutemov.name> <20170125165522.GA11569@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20170125165522.GA11569@linux.vnet.ibm.com> Sender: owner-linux-mm@kvack.org List-ID: To: Srikar Dronamraju Cc: Andrew Morton , "Kirill A. Shutemov" , Andrea Arcangeli , Hugh Dickins , Rik van Riel , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Oleg Nesterov , Peter Zijlstra On Wed, Jan 25, 2017 at 08:55:22AM -0800, Srikar Dronamraju wrote: > > > > > > > For THPs page_check_address() always fails. It's better to split them > > > > first before trying to replace. > > > > > > So what does this mean. uprobes simply fails to work when trying to > > > place a probe into a THP memory region? > > > > Looks like we can end up with endless retry loop in uprobe_write_opcode(). > > > > > How come nobody noticed (and reported) this when using the feature? > > > > I guess it's not often used for anon memory. > > > > The first time the breakpoint is hit on a page, it replaces the text > page with anon page. Now lets assume we insert breakpoints in all the > pages in a range. Here each page is individually replaced by a non THP > anonpage. (since we dont have bulk breakpoint insertion support, > breakpoint insertion happens one at a time). Now the only interesting > case may be when each of these replaced pages happen to be physically > contiguous so that THP kicks in to replace all of these pages with one > THP page. Can happen in practice? The problem is with the page you try to replace, not with page that you replace it with. > Are there any other cases that I have missed? The binary on tmpfs with huge pages. I wrote test-case that triggers the problem. -- Kirill A. Shutemov -- 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: email@kvack.org