From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-yh0-f46.google.com (mail-yh0-f46.google.com [209.85.213.46]) by kanga.kvack.org (Postfix) with ESMTP id E921B6B0032 for ; Tue, 13 Jan 2015 18:48:52 -0500 (EST) Received: by mail-yh0-f46.google.com with SMTP id t59so2996514yho.5 for ; Tue, 13 Jan 2015 15:48:52 -0800 (PST) Received: from mail.linuxfoundation.org (mail.linuxfoundation.org. [140.211.169.12]) by mx.google.com with ESMTPS id o82si11431339yko.30.2015.01.13.15.48.51 for (version=TLSv1.2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Tue, 13 Jan 2015 15:48:51 -0800 (PST) Date: Tue, 13 Jan 2015 15:48:49 -0800 From: Andrew Morton Subject: Re: [PATCH 0/5] kstrdup optimization Message-Id: <20150113154849.5bb3fdd0ff9d73a89e639f19@linux-foundation.org> In-Reply-To: References: <1421054323-14430-1-git-send-email-a.hajda@samsung.com> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Geert Uytterhoeven Cc: Andrzej Hajda , Linux MM , Marek Szyprowski , Kyungmin Park , "linux-kernel@vger.kernel.org" , Andi Kleen , Andreas Mohr , Mike Turquette , Alexander Viro On Mon, 12 Jan 2015 21:45:58 +0100 Geert Uytterhoeven wrote: > On Mon, Jan 12, 2015 at 10:18 AM, Andrzej Hajda wrote: > > kstrdup if often used to duplicate strings where neither source neither > > destination will be ever modified. In such case we can just reuse the source > > instead of duplicating it. The problem is that we must be sure that > > the source is non-modifiable and its life-time is long enough. > > > > I suspect the good candidates for such strings are strings located in kernel > > .rodata section, they cannot be modifed because the section is read-only and > > their life-time is equal to kernel life-time. > > > > This small patchset proposes alternative version of kstrdup - kstrdup_const, > > which returns source string if it is located in .rodata otherwise it fallbacks > > to kstrdup. > > It also introduces kfree_const(const void *x). > > As kfree_const() has the exact same signature as kfree(), the risk of > accidentally passing pointers returned from kstrdup_const() to kfree() seems > high, which may lead to memory corruption if the pointer doesn't point to > allocated memory. Yes, it's an ugly little patchset. But 100-200k of memory is hard to argue with, and I'm not seeing a practical way of getting those savings with a cleaner approach. Hopefully a kfree(rodata-address) will promptly oops, but I haven't tested that and it presumably depends on which flavour of slab/sleb/slib/slob/slub you're using. -- 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