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[99.254.144.39]) by smtp.gmail.com with ESMTPSA id 2-20020a05620a070200b0077413b342e9sm53812qkc.128.2023.10.19.12.53.01 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 19 Oct 2023 12:53:03 -0700 (PDT) Date: Thu, 19 Oct 2023 15:53:01 -0400 From: Peter Xu To: David Hildenbrand Cc: Lokesh Gidra , Suren Baghdasaryan , akpm@linux-foundation.org, viro@zeniv.linux.org.uk, brauner@kernel.org, shuah@kernel.org, aarcange@redhat.com, hughd@google.com, mhocko@suse.com, axelrasmussen@google.com, rppt@kernel.org, willy@infradead.org, Liam.Howlett@oracle.com, jannh@google.com, zhangpeng362@huawei.com, bgeffon@google.com, kaleshsingh@google.com, ngeoffray@google.com, jdduke@google.com, linux-mm@kvack.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org, kernel-team@android.com Subject: Re: [PATCH v3 2/3] userfaultfd: UFFDIO_MOVE uABI Message-ID: References: <478697aa-f55c-375a-6888-3abb343c6d9d@redhat.com> <205abf01-9699-ff1c-3e4e-621913ada64e@redhat.com> <12588295-2616-eb11-43d2-96a3c62bd181@redhat.com> <8d187891-f131-4912-82d8-13112125b210@redhat.com> Precedence: bulk X-Mailing-List: linux-fsdevel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: On Thu, Oct 19, 2023 at 05:41:01PM +0200, David Hildenbrand wrote: > That's not my main point. It can easily become a maintenance burden without > any real use cases yet that we are willing to support. That's why I requested a few times that we can discuss the complexity of cross-mm support already here, and I'm all ears if I missed something on the "maintenance burden" part.. I started by listing what I think might be different, and we can easily speedup single-mm with things like "if (ctx->mm != mm)" checks with e.g. memcg, just like what this patch already did with pgtable depositions. We keep saying "maintenance burden" but we refuse to discuss what is that.. I'll leave that to Suren and Lokesh to decide. For me the worst case is one more flag which might be confusing, which is not the end of the world.. Suren, you may need to work more thoroughly to remove cross-mm implications if so, just like when renaming REMAP to MOVE. Thanks, -- Peter Xu