From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <SRS0=Pa3/=3G=kvack.org=owner-linux-mm@kernel.org>
X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on
	aws-us-west-2-korg-lkml-1.web.codeaurora.org
X-Spam-Level: 
X-Spam-Status: No, score=-0.8 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED,
	DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,
	SPF_PASS autolearn=no autolearn_force=no version=3.4.0
Received: from mail.kernel.org (mail.kernel.org [198.145.29.99])
	by smtp.lore.kernel.org (Postfix) with ESMTP id 262FFC33CAF
	for <linux-mm@archiver.kernel.org>; Fri, 17 Jan 2020 03:16:12 +0000 (UTC)
Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17])
	by mail.kernel.org (Postfix) with ESMTP id DB10E20684
	for <linux-mm@archiver.kernel.org>; Fri, 17 Jan 2020 03:16:11 +0000 (UTC)
Authentication-Results: mail.kernel.org;
	dkim=pass (1024-bit key) header.d=kernel.org header.i=@kernel.org header.b="PxYqemw+"
DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org DB10E20684
Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=linux-foundation.org
Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org
Received: by kanga.kvack.org (Postfix)
	id 705206B030E; Thu, 16 Jan 2020 22:16:11 -0500 (EST)
Received: by kanga.kvack.org (Postfix, from userid 40)
	id 6DCD96B030F; Thu, 16 Jan 2020 22:16:11 -0500 (EST)
X-Delivered-To: int-list-linux-mm@kvack.org
Received: by kanga.kvack.org (Postfix, from userid 63042)
	id 618C56B0310; Thu, 16 Jan 2020 22:16:11 -0500 (EST)
X-Delivered-To: linux-mm@kvack.org
Received: from forelay.hostedemail.com (smtprelay0253.hostedemail.com [216.40.44.253])
	by kanga.kvack.org (Postfix) with ESMTP id 496AD6B030E
	for <linux-mm@kvack.org>; Thu, 16 Jan 2020 22:16:11 -0500 (EST)
Received: from smtpin24.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251])
	by forelay02.hostedemail.com (Postfix) with SMTP id F0F05D38
	for <linux-mm@kvack.org>; Fri, 17 Jan 2020 03:16:10 +0000 (UTC)
X-FDA: 76385662500.24.form72_8d41f5d32282f
X-HE-Tag: form72_8d41f5d32282f
X-Filterd-Recvd-Size: 2335
Received: from mail.kernel.org (mail.kernel.org [198.145.29.99])
	by imf25.hostedemail.com (Postfix) with ESMTP
	for <linux-mm@kvack.org>; Fri, 17 Jan 2020 03:16:10 +0000 (UTC)
Received: from X1 (nat-ab2241.sltdut.senawave.net [162.218.216.4])
	(using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits))
	(No client certificate requested)
	by mail.kernel.org (Postfix) with ESMTPSA id BE85220679;
	Fri, 17 Jan 2020 03:16:09 +0000 (UTC)
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org;
	s=default; t=1579230969;
	bh=Pv2hU0kC+NNhp2G0ieTjOr4w9ey+PNyLJxlmNWkf/j4=;
	h=Date:From:To:Cc:Subject:In-Reply-To:References:From;
	b=PxYqemw+WtaVcgnGoE30v238L3q61frkBF7mDd9rfw2Li3dIWg6z/0I805u3XKDLz
	 AZMCUCujV11mMjaPdcQLcHrgZhDfI88Bod1Avr6KwaH3JOY68+8ZqpfUgw0gUZfTDp
	 NjsAvGFq3rCcT3rIqmOZcdhFIPzT78HTOTXokPPA=
Date: Thu, 16 Jan 2020 19:16:09 -0800
From: Andrew Morton <akpm@linux-foundation.org>
To: David Rientjes <rientjes@google.com>
Cc: Mel Gorman <mgorman@techsingularity.net>, Vlastimil Babka
 <vbabka@suse.cz>, linux-kernel@vger.kernel.org, linux-mm@kvack.org
Subject: Re: [patch] mm, thp: fix defrag setting if newline is not used
Message-Id: <20200116191609.3972fd5301cf364a27381923@linux-foundation.org>
In-Reply-To: <alpine.DEB.2.21.2001141757490.108121@chino.kir.corp.google.com>
References: <alpine.DEB.2.21.2001141757490.108121@chino.kir.corp.google.com>
X-Mailer: Sylpheed 3.5.1 (GTK+ 2.24.32; x86_64-pc-linux-gnu)
Mime-Version: 1.0
Content-Type: text/plain; charset=US-ASCII
Content-Transfer-Encoding: 7bit
X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4
Sender: owner-linux-mm@kvack.org
Precedence: bulk
X-Loop: owner-majordomo@kvack.org
List-ID: <linux-mm.kvack.org>

On Tue, 14 Jan 2020 17:58:36 -0800 (PST) David Rientjes <rientjes@google.com> wrote:

> If thp defrag setting "defer" is used and a newline is *not* used when
> writing to the sysfs file, this is interpreted as the "defer+madvise"
> option.
> 
> This is because we do prefix matching and if five characters are written
> without a newline, the current code ends up comparing to the first five
> bytes of the "defer+madvise" option and using that instead.
> 
> Find the length of what the user is writing and use that to guide our
> decision on which string comparison to do.

Gee, why is this code so complicated?  Can't we just do

	if (sysfs_streq(buf, "always")) {
		...
	} else if sysfs_streq(buf, "defer+madvise")) {
		...
	}
	...