From mboxrd@z Thu Jan 1 00:00:00 1970 From: Al Viro Date: Mon, 21 Sep 2020 15:29:37 +0000 Subject: Re: [PATCH 02/11] mm: call import_iovec() instead of rw_copy_check_uvector() in process_vm_rw() Message-Id: <20200921152937.GX3421308@ZenIV.linux.org.uk> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit List-Id: References: <20200921143434.707844-1-hch@lst.de> <20200921143434.707844-3-hch@lst.de> <20200921150211.GS3421308@ZenIV.linux.org.uk> In-Reply-To: To: David Laight Cc: Christoph Hellwig , Andrew Morton , Jens Axboe , Arnd Bergmann , David Howells , "linux-arm-kernel@lists.infradead.org" , "linux-kernel@vger.kernel.org" , "linux-mips@vger.kernel.org" , "linux-parisc@vger.kernel.org" , "linuxppc-dev@lists.ozlabs.org" , "linux-s390@vger.kernel.org" , "sparclinux@vger.kernel.org" , "linux-block@vger.kernel.org" , "linux-scsi@vger.kernel.org" , "linux-fsdevel@vger.kernel.org" , "linux-aio@kvack.org" , "io-uring@vger.kernel.org" , "linux-arch@vger.kernel.org" , "linux-mm@kvack.org" , "netdev@vger.kernel.org" , "keyrings@vger.kernel.org" , "linux-security-module@vger.kernel.org" On Mon, Sep 21, 2020 at 03:21:35PM +0000, David Laight wrote: > You really don't want to be looping through the array twice. Profiles, please. > I think the 'length' check can be optimised to do something like: > for (...) { > ssize_t len = (ssize_t)iov[seg].iov_len; > ret += len; > len_hi += (unsigned long)len >> 20; > } > if (len_hi) { > /* Something potentially odd in the lengths. > * Might just be a very long fragment. > * Check the individial values. */ > Add the exiting loop here. > } Far too ugly to live.