From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758719AbZEaK3A (ORCPT ); Sun, 31 May 2009 06:29:00 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752616AbZEaK2w (ORCPT ); Sun, 31 May 2009 06:28:52 -0400 Received: from courier.cs.helsinki.fi ([128.214.9.1]:42673 "EHLO mail.cs.helsinki.fi" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751330AbZEaK2w (ORCPT ); Sun, 31 May 2009 06:28:52 -0400 Message-ID: <4A225ADD.5070605@cs.helsinki.fi> Date: Sun, 31 May 2009 13:24:29 +0300 From: Pekka Enberg User-Agent: Thunderbird 2.0.0.21 (Macintosh/20090302) MIME-Version: 1.0 To: Alan Cox CC: Rik van Riel , Ingo Molnar , "Larry H." , linux-kernel@vger.kernel.org, Linus Torvalds , linux-mm@kvack.org, Ingo Molnar , pageexec@freemail.hu, Linus Torvalds Subject: Re: [patch 0/5] Support for sanitization flag in low-level page allocator References: <20090528090836.GB6715@elte.hu> <20090530082048.GM29711@oblivion.subreption.com> <20090530173428.GA20013@elte.hu> <20090530180333.GH6535@oblivion.subreption.com> <20090530182113.GA25237@elte.hu> <20090530184534.GJ6535@oblivion.subreption.com> <20090530190828.GA31199@elte.hu> <4A21999E.5050606@redhat.com> <84144f020905301353y2f8c232na4c5f9dfb740eec4@mail.gmail.com> <20090531001052.40ac57d2@lxorguk.ukuu.org.uk> <84144f020905302314w12c4c7f8jc8241e36c847f53e@mail.gmail.com> <20090531112440.50cbc4fd@lxorguk.ukuu.org.uk> In-Reply-To: <20090531112440.50cbc4fd@lxorguk.ukuu.org.uk> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Alan, On Sun, May 31, 2009 at 2:10 AM, Alan Cox wrote: >>> #2 Using kzfree() to clear specific bits of memory (and I question the >>> kzfree implementation as it seems ksize can return numbers much much >>> bigger than the allocated space you need to clear - correct but oversize) >>> or using other flags. I'd favour kzfree personally (and fixing it to work >>> properly) >> Well, yes, that's what kzfree() needs to do given the current API. I >> am not sure why you think it's a problem, though. Adding a size >> argument to the function will make it more error prone. Alan Cox wrote: > Definitely - am I right however that > > x = kzalloc(size, flags) > blah > kzfree(x) > > can memset a good deal more memory (still safely) than "size" to zero ? Yes because we actually _allocate_ more than requested the 'size' and the generic allocator has no way of knowing whether how much of the allocated region was actually used by the caller. Alan Cox wrote: > That has performance relevance if so and it ought to at least be > documented. Makes sense. Pekka From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail138.messagelabs.com (mail138.messagelabs.com [216.82.249.35]) by kanga.kvack.org (Postfix) with ESMTP id 557C26B004F for ; Sun, 31 May 2009 06:28:29 -0400 (EDT) Message-ID: <4A225ADD.5070605@cs.helsinki.fi> Date: Sun, 31 May 2009 13:24:29 +0300 From: Pekka Enberg MIME-Version: 1.0 Subject: Re: [patch 0/5] Support for sanitization flag in low-level page allocator References: <20090528090836.GB6715@elte.hu> <20090530082048.GM29711@oblivion.subreption.com> <20090530173428.GA20013@elte.hu> <20090530180333.GH6535@oblivion.subreption.com> <20090530182113.GA25237@elte.hu> <20090530184534.GJ6535@oblivion.subreption.com> <20090530190828.GA31199@elte.hu> <4A21999E.5050606@redhat.com> <84144f020905301353y2f8c232na4c5f9dfb740eec4@mail.gmail.com> <20090531001052.40ac57d2@lxorguk.ukuu.org.uk> <84144f020905302314w12c4c7f8jc8241e36c847f53e@mail.gmail.com> <20090531112440.50cbc4fd@lxorguk.ukuu.org.uk> In-Reply-To: <20090531112440.50cbc4fd@lxorguk.ukuu.org.uk> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org To: Alan Cox Cc: Rik van Riel , Ingo Molnar , "Larry H." , linux-kernel@vger.kernel.org, Linus Torvalds , linux-mm@kvack.org, Ingo Molnar , pageexec@freemail.hu, Linus Torvalds List-ID: Hi Alan, On Sun, May 31, 2009 at 2:10 AM, Alan Cox wrote: >>> #2 Using kzfree() to clear specific bits of memory (and I question the >>> kzfree implementation as it seems ksize can return numbers much much >>> bigger than the allocated space you need to clear - correct but oversize) >>> or using other flags. I'd favour kzfree personally (and fixing it to work >>> properly) >> Well, yes, that's what kzfree() needs to do given the current API. I >> am not sure why you think it's a problem, though. Adding a size >> argument to the function will make it more error prone. Alan Cox wrote: > Definitely - am I right however that > > x = kzalloc(size, flags) > blah > kzfree(x) > > can memset a good deal more memory (still safely) than "size" to zero ? Yes because we actually _allocate_ more than requested the 'size' and the generic allocator has no way of knowing whether how much of the allocated region was actually used by the caller. Alan Cox wrote: > That has performance relevance if so and it ought to at least be > documented. Makes sense. Pekka -- 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