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Fri, 10 Apr 2020 16:11:41 -0700 (PDT) Received: from google.com ([2601:647:4001:3000::50e3]) by smtp.gmail.com with ESMTPSA id 15sm2629073pfu.186.2020.04.10.16.11.38 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 10 Apr 2020 16:11:39 -0700 (PDT) Date: Fri, 10 Apr 2020 16:11:36 -0700 From: Minchan Kim To: Sergey Senozhatsky Subject: Re: [PATCH 10/28] mm: only allow page table mappings for built-in zsmalloc Message-ID: <20200410231136.GA101325@google.com> References: <20200408115926.1467567-1-hch@lst.de> <20200408115926.1467567-11-hch@lst.de> <20200409160826.GC247701@google.com> <20200409165030.GG20713@hirez.programming.kicks-ass.net> <20200409170813.GD247701@google.com> <20200410023845.GA2354@jagdpanzerIV.localdomain> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200410023845.GA2354@jagdpanzerIV.localdomain> X-BeenThere: linuxppc-dev@lists.ozlabs.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: linux-hyperv@vger.kernel.org, Peter Zijlstra , dri-devel@lists.freedesktop.org, linux-mm@kvack.org, "K. Y. Srinivasan" , Sumit Semwal , linux-arch@vger.kernel.org, linux-s390@vger.kernel.org, Wei Liu , Stephen Hemminger , x86@kernel.org, Christoph Hellwig , David Airlie , Laura Abbott , Nitin Gupta , Daniel Vetter , Haiyang Zhang , linaro-mm-sig@lists.linaro.org, bpf@vger.kernel.org, linux-arm-kernel@lists.infradead.org, Robin Murphy , linux-kernel@vger.kernel.org, iommu@lists.linux-foundation.org, Sakari Ailus , Andrew Morton , linuxppc-dev@lists.ozlabs.org Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" Hi Sergey, On Fri, Apr 10, 2020 at 11:38:45AM +0900, Sergey Senozhatsky wrote: > On (20/04/09 10:08), Minchan Kim wrote: > > > > Even though I don't know how many usecase we have using zsmalloc as > > > > module(I heard only once by dumb reason), it could affect existing > > > > users. Thus, please include concrete explanation in the patch to > > > > justify when the complain occurs. > > > > > > The justification is 'we can unexport functions that have no sane reason > > > of being exported in the first place'. > > > > > > The Changelog pretty much says that. > > > > Okay, I hope there is no affected user since this patch. > > If there are someone, they need to provide sane reason why they want > > to have zsmalloc as module. > > I'm one of those who use zsmalloc as a module - mainly because I use zram > as a compressing general purpose block device, not as a swap device. > I create zram0, mkfs, mount, checkout and compile code, once done - > umount, rmmod. This reduces the number of writes to SSD. Some people use > tmpfs, but zram device(-s) can be much larger in size. That's a niche use > case and I'm not against the patch. It doesn't mean we couldn't use zsmalloc as module any longer. It means we couldn't use zsmalloc as module with pgtable mapping whcih was little bit faster on microbenchmark in some architecutre(However, I usually temped to remove it since it had several problems). However, we could still use zsmalloc as module as copy way instead of pgtable mapping. Thus, if someone really want to rollback the feature, they should provide reasonable reason why it doesn't work for them. "A little fast" wouldn't be enough to exports deep internal to the module. Thanks.