From: Eric Sandeen Subject: Re: [PATCH 5 2/4] Return 32/64-bit dir name hash according to usage type Date: Mon, 23 Apr 2012 15:37:06 -0500 Message-ID: <4F95BD72.6090200@redhat.com> References: <20120109132137.2616029.76288.stgit@localhost.localdomain> <20120109132148.2616029.68798.stgit@localhost.localdomain> <4F91C15B.6070200@redhat.com> <4F93FED6.6090505@itwm.fraunhofer.de> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Cc: linux-nfs@vger.kernel.org, linux-ext4@vger.kernel.org, linux-fsdevel@vger.kernel.org, Fan Yong , bfields@redhat.com, Andreas Dilger To: Bernd Schubert Return-path: In-Reply-To: <4F93FED6.6090505@itwm.fraunhofer.de> Sender: linux-fsdevel-owner@vger.kernel.org List-Id: linux-ext4.vger.kernel.org On 4/22/12 7:51 AM, Bernd Schubert wrote: > On 04/20/2012 10:04 PM, Eric Sandeen wrote: >> On 1/9/12 7:21 AM, Bernd Schubert wrote: >>> From: Fan Yong >>> >>> Traditionally ext2/3/4 has returned a 32-bit hash value from llseek() >>> to appease NFSv2, which can only handle a 32-bit cookie for seekdir() >>> and telldir(). However, this causes problems if there are 32-bit hash >>> collisions, since the NFSv2 server can get stuck resending the same >>> entries from the directory repeatedly. >>> >>> Allow ext4 to return a full 64-bit hash (both major and minor) for >>> telldir to decrease the chance of hash collisions. This still needs >>> integration on the NFS side. >>> >>> Patch-updated-by: Bernd Schubert >>> (blame me if something is not correct) >> >> Bernd, I've merged this to ext3. Bruce thought maybe you were working >> on the same. Should I send mine? > > That is perfectly fine with me. > >> >> Also... >> >>> +/* >>> + * ext4_dir_llseek() based on generic_file_llseek() to handle both >>> + * non-htree and htree directories, where the "offset" is in terms >>> + * of the filename hash value instead of the byte offset. >>> + * >>> + * NOTE: offsets obtained *before* ext4_set_inode_flag(dir, EXT4_INODE_INDEX) >>> + * will be invalid once the directory was converted into a dx directory >>> + */ >>> +loff_t ext4_dir_llseek(struct file *file, loff_t offset, int origin) >> >> ext4_llseek() worries about max offset for direct/indirect vs. extent-mapped >> files. Do we need to worry about the same thing in this function? > > Hrmm, I just checked it and I think either is wrong. We only have to > care about non-dx directories, so ext4_readdir() applies, which limits > filp->f_pos < inode->i_size. > Going to send a patch tomorrow. Thanks for spotting this! The other thing I'm wondering is whether, in light of ef3d0fd27e90f67e35da516dafc1482c82939a60 vfs: do (nearly) lockless generic_file_llseek taking the i_mutex in ext4_dir_llseek could be a perf regression vs what was there before? Is there anything about the new function which requires stronger locking? I may be missing something obvious about the nfs interaction, not sure. -Eric > Cheers, > Bernd > > > > -- > To unsubscribe from this list: send the line "unsubscribe linux-ext4" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html