Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932767AbcKYQjS (ORCPT ); Fri, 25 Nov 2016 11:39:18 -0500 Received: from mail-vk0-f65.google.com ([209.85.213.65]:35850 "EHLO mail-vk0-f65.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932162AbcKYQjN (ORCPT ); Fri, 25 Nov 2016 11:39:13 -0500 MIME-Version: 1.0 In-Reply-To: References: <20161115165538.878698352bd45e212751b57a@gmail.com> <20161115170030.f0396011fa00423ff711a3b4@gmail.com> From: Vitaly Wool Date: Fri, 25 Nov 2016 17:25:42 +0100 Message-ID: Subject: Re: [PATCH 2/3] z3fold: don't fail kernel build if z3fold_header is too big To: Dan Streetman Cc: Linux-MM , linux-kernel , Andrew Morton , Arnd Bergmann 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: 2030 Lines: 52 On Fri, Nov 25, 2016 at 4:59 PM, Dan Streetman wrote: > On Tue, Nov 15, 2016 at 11:00 AM, Vitaly Wool wrote: >> Currently the whole kernel build will be stopped if the size of >> struct z3fold_header is greater than the size of one chunk, which >> is 64 bytes by default. This may stand in the way of automated >> test/debug builds so let's remove that and just fail the z3fold >> initialization in such case instead. >> >> Signed-off-by: Vitaly Wool >> --- >> mm/z3fold.c | 11 ++++++++--- >> 1 file changed, 8 insertions(+), 3 deletions(-) >> >> diff --git a/mm/z3fold.c b/mm/z3fold.c >> index 7ad70fa..ffd9353 100644 >> --- a/mm/z3fold.c >> +++ b/mm/z3fold.c >> @@ -870,10 +870,15 @@ MODULE_ALIAS("zpool-z3fold"); >> >> static int __init init_z3fold(void) >> { >> - /* Make sure the z3fold header will fit in one chunk */ >> - BUILD_BUG_ON(sizeof(struct z3fold_header) > ZHDR_SIZE_ALIGNED); > > Nak. this is the wrong way to handle this. The build bug is there to > indicate to you that your patch makes the header too large, not as a > runtime check to disable everything. Okay, let's agree to drop it. > The right way to handle it is to change the hardcoded assumption that > the header fits into a single chunk; e.g.: > > #define ZHDR_SIZE_ALIGNED round_up(sizeof(struct z3fold_header), CHUNK_SIZE) > #define ZHDR_CHUNKS (ZHDR_SIZE_ALIGNED >> CHUNK_SHIFT) > > then use ZHDR_CHUNKS in all places where it's currently assumed the > header is 1 chunk, e.g. in num_free_chunks: > > if (zhdr->middle_chunks != 0) { > int nfree_before = zhdr->first_chunks ? > - 0 : zhdr->start_middle - 1; > + 0 : zhdr->start_middle - ZHDR_CHUNKS; > > after changing all needed places like that, the build bug isn't needed > anymore (unless we want to make sure the header isn't larger than some > arbitrary number N chunks) That sounds overly complicated to me. I would rather use bit_spin_lock as Arnd suggested. What would you say? ~vitaly