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Wed, 27 Mar 2024 11:57:02 -0700 (PDT) X-Google-Smtp-Source: AGHT+IH8ZLok88R0OgZXibxpbpVWGqPZ88QA+3LjCUsYCfI3W3udUs2WL1Xfomla6duh8BwZ8ZRucA== X-Received: by 2002:a05:6820:e0f:b0:5a5:5ed9:b246 with SMTP id el15-20020a0568200e0f00b005a55ed9b246mr998422oob.0.1711565822369; Wed, 27 Mar 2024 11:57:02 -0700 (PDT) Received: from x1n ([99.254.121.117]) by smtp.gmail.com with ESMTPSA id eq17-20020a05622a5e1100b004313f54aaa9sm4895159qtb.5.2024.03.27.11.57.01 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 27 Mar 2024 11:57:02 -0700 (PDT) Date: Wed, 27 Mar 2024 14:56:59 -0400 From: Peter Xu To: Peng Zhang Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, akpm@linux-foundation.org, david@redhat.com, axelrasmussen@google.com, surenb@google.com, lokeshgidra@google.com, Liam.Howlett@oracle.com, wangkefeng.wang@huawei.com, sunnanyong@huawei.com Subject: Re: [PATCH] userfaultfd: early return in dup_userfaultfd() Message-ID: References: <20240327090835.3232629-1-zhangpeng362@huawei.com> Precedence: bulk X-Mailing-List: linux-kernel@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: <20240327090835.3232629-1-zhangpeng362@huawei.com> On Wed, Mar 27, 2024 at 05:08:35PM +0800, Peng Zhang wrote: > From: ZhangPeng > > When vma->vm_userfaultfd_ctx.ctx is NULL, vma->vm_flags should have > cleared __VM_UFFD_FLAGS. Therefore, there is no need to down_write or > clear the flag, which will affect fork performance. Fix this by > returning early if octx is NULL in dup_userfaultfd(). > > By applying this patch we can get a 1.3% performance improvement for > lmbench fork_prot. Results are as follows: > base early return > Process fork+exit: 419.1106 413.4804 > > Signed-off-by: ZhangPeng Reviewed-by: Peter Xu -- Peter Xu