From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1759918AbYFEQKo (ORCPT ); Thu, 5 Jun 2008 12:10:44 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751397AbYFEQKg (ORCPT ); Thu, 5 Jun 2008 12:10:36 -0400 Received: from waste.org ([66.93.16.53]:49246 "EHLO waste.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750764AbYFEQKf (ORCPT ); Thu, 5 Jun 2008 12:10:35 -0400 Subject: Re: [PATCH 3/5] pagemap: Make pagemap_read enforce reading in multiples of 8 From: Matt Mackall To: Thomas Tuttle Cc: akpm@linux-foundation.org, linux-kernel@vger.kernel.org In-Reply-To: <4ca0a85e0806050905j6cf33f3dx9143333aa0a8b6e7@mail.gmail.com> References: <4ca0a85e0806050806r38de18dft8927e093a8e47abd@mail.gmail.com> <1212681822.3953.162.camel@calx> <4ca0a85e0806050905j6cf33f3dx9143333aa0a8b6e7@mail.gmail.com> Content-Type: text/plain Date: Thu, 05 Jun 2008 11:09:35 -0500 Message-Id: <1212682175.3953.169.camel@calx> Mime-Version: 1.0 X-Mailer: Evolution 2.12.3 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, 2008-06-05 at 12:05 -0400, Thomas Tuttle wrote: > On Thu, Jun 5, 2008 at 12:03 PM, Matt Mackall wrote: > > > > On Thu, 2008-06-05 at 11:06 -0400, Thomas Tuttle wrote: > >> Since kpagecount and kpageflags require reads in multiples of 8, and > >> it simplifies add_to_pagemap significantly, I added the same > >> requirement to /proc/pid/pagemap. > > > > I'm generally fine with this. Another approach that's perhaps more > > friendly is when someone tries to do a 24-byte read, do a 16-byte read, > > leaving the file pointer aligned. Not sure if that's completely kosher > > though. > > This doesn't require that they read exactly 8 bytes, just that they > read some multiple of 8 bytes. (They can read 8, 16, 24, etc..., just > not something like 12.) Yes, I got that, I'm just mathematically impaired this morning. Read that as "when someone tries to do a *20* byte read, do a 16-byte read.." In other words, round down to the nearest multiple of 8. -- Mathematics is the supreme nostalgia of our time.