Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753589AbcKYQJs (ORCPT ); Fri, 25 Nov 2016 11:09:48 -0500 Received: from mail-ua0-f193.google.com ([209.85.217.193]:33783 "EHLO mail-ua0-f193.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754189AbcKYQJi (ORCPT ); Fri, 25 Nov 2016 11:09:38 -0500 MIME-Version: 1.0 In-Reply-To: <3177176.drX8hSSUx4@wuerfel> References: <20161124163158.3939337-1-arnd@arndb.de> <1480007330.19726.11.camel@perches.com> <3177176.drX8hSSUx4@wuerfel> From: Vitaly Wool Date: Fri, 25 Nov 2016 16:51:03 +0100 Message-ID: Subject: Re: [PATCH] z3fold: use %z modifier for format string To: Arnd Bergmann Cc: Joe Perches , Andrew Morton , Dan Streetman , zhong jiang , Linux-MM , LKML Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2218 Lines: 48 On Fri, Nov 25, 2016 at 9:41 AM, Arnd Bergmann wrote: > On Friday, November 25, 2016 8:38:25 AM CET Vitaly Wool wrote: >> >> diff --git a/mm/z3fold.c b/mm/z3fold.c >> >> index e282ba073e77..66ac7a7dc934 100644 >> >> --- a/mm/z3fold.c >> >> +++ b/mm/z3fold.c >> >> @@ -884,7 +884,7 @@ static int __init init_z3fold(void) >> >> { >> >> /* Fail the initialization if z3fold header won't fit in one chunk */ >> >> if (sizeof(struct z3fold_header) > ZHDR_SIZE_ALIGNED) { >> >> - pr_err("z3fold: z3fold_header size (%d) is bigger than " >> >> + pr_err("z3fold: z3fold_header size (%zd) is bigger than " >> >> "the chunk size (%d), can't proceed\n", >> >> sizeof(struct z3fold_header) , ZHDR_SIZE_ALIGNED); >> >> return -E2BIG; >> > >> > The embedded "z3fold: " prefix here should be removed >> > as there's a pr_fmt that also adds it. >> > >> > The test looks like it should be a BUILD_BUG_ON rather >> > than any runtime test too. >> >> It used to be BUILD_BUG_ON but we deliberately changed that because >> sizeof(spinlock_t) gets bloated in debug builds, so it just won't >> build with default CHUNK_SIZE. > > Could this be improved by making the CHUNK_SIZE bigger depending on > the debug options? I don't see how silently enforcing a suboptimal configuration is better than failing the initialization (so that you can adjust CHUNK_SIZE yourself). I can add something descriptive to Documentation/vm/z3fold.txt for that matter. > Alternatively, how about using a bit_spin_lock instead of raw_spin_lock? > That would guarantee a fixed size for the lock and make z3fold_header > always 24 bytes (on 32-bit architectures) or 40 bytes > (on 64-bit architectures). You could even play some tricks with the > first_num field to make it fit in the same word as the lock and make the > structure fit into 32 bytes if you care about that. That is interesting. Actually I can have that bit in page->private and then I don't need to handle headless pages in a special way, that sounds appealing. However, there is a warning about bit_spin_lock performance penalty. Do you know how big it is? Best regards, Vitaly