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[71.184.117.43]) by smtp.gmail.com with ESMTPSA id p7sm8247131qki.61.2020.06.26.12.24.31 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 26 Jun 2020 12:24:32 -0700 (PDT) Date: Fri, 26 Jun 2020 15:24:26 -0400 From: Qian Cai To: Dave Hansen Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, ben.widawsky@intel.com, alex.shi@linux.alibaba.com, dwagner@suse.de, tobin@kernel.org, cl@linux.com, akpm@linux-foundation.org, stable@kernel.org Subject: Re: [PATCH] mm/vmscan: restore zone_reclaim_mode ABI Message-ID: <20200626192426.GA4329@lca.pw> References: <20200626003459.D8E015CA@viggo.jf.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200626003459.D8E015CA@viggo.jf.intel.com> Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Jun 25, 2020 at 05:34:59PM -0700, Dave Hansen wrote: > > From: Dave Hansen > > I went to go add a new RECLAIM_* mode for the zone_reclaim_mode > sysctl. Like a good kernel developer, I also went to go update the > documentation. I noticed that the bits in the documentation didn't > match the bits in the #defines. > > The VM evidently stopped caring about RECLAIM_ZONE at some point (or > never cared) and the #define itself was later removed as a cleanup. > Those things by themselves are fine. > > But, the _other_ bit locations also got changed. That's not OK because > the bit values are documented to mean one specific thing and users > surely rely on them meaning that one thing and not changing from > kernel to kernel. The end result is that if someone had a script > that did: > > sysctl vm.zone_reclaim_mode=1 > > That script went from doing nothing to writing out pages during > node reclaim after the commit in question. That's not great. > > Put the bits back the way they were and add a comment so something > like this is a bit harder to do again. Update the documentation to > make it clear that the first bit is ignored. > > Signed-off-by: Dave Hansen > Fixes: commit 648b5cf368e0 ("mm/vmscan: remove unused RECLAIM_OFF/RECLAIM_ZONE") This is a wrong format.