From: Eric Sandeen Subject: Re: [PATCH v2] e2fsprogs: Limit number of reserved gdt blocks on small fs Date: Mon, 27 Apr 2015 11:23:19 -0500 Message-ID: <553E6277.3040800@redhat.com> References: <1427280382-31120-1-git-send-email-lczerner@redhat.com> <553ABAF0.2020702@redhat.com> <20150427161451.GA22448@quack.suse.cz> Mime-Version: 1.0 Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit Cc: Lukas Czerner , linux-ext4@vger.kernel.org To: Jan Kara , Andreas Dilger Return-path: Received: from mx1.redhat.com ([209.132.183.28]:47452 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752967AbbD0QXZ (ORCPT ); Mon, 27 Apr 2015 12:23:25 -0400 In-Reply-To: <20150427161451.GA22448@quack.suse.cz> Sender: linux-ext4-owner@vger.kernel.org List-ID: On 4/27/15 11:14 AM, Jan Kara wrote: > On Fri 24-04-15 22:25:06, Andreas Dilger wrote: >> On Apr 24, 2015, at 3:51 PM, Eric Sandeen wrote: >>> On 3/25/15 5:46 AM, Lukas Czerner wrote: >>>> Currently we're unable to online resize very small (smaller than 32 MB) >>>> file systems with 1k block size because there is not enough space in the >>>> journal to put all the reserved gdt blocks. >>> >>> So, I'll get to the patch review if I need to, but this all seemed a little >>> odd; this is a regression, so do we really need to restrict things at mkfs >>> time? >>> >>> On the userspace side, things were ok until: >>> >>> 9f6ba88 resize2fs: add support for new in-kernel online resize ioctl >>> >>> and even with that, on the kernelspace side, things were ok until: >>> >>> 8f7d89f jbd2: transaction reservation support >>> >>> I guess I'm trying to understand why that jbd2 commit regressed this. >>> I've not been paying enough attention to ext4 lately. ;) >>> >>> I mean, the threshold got chopped in half: >>> >>> - if (nblocks > journal->j_max_transaction_buffers) { >>> + /* >>> + * 1/2 of transaction can be reserved so we can practically handle >>> + * only 1/2 of maximum transaction size per operation >>> + */ >>> + if (WARN_ON(blocks > journal->j_max_transaction_buffers / 2)) { >>> printk(KERN_ERR "JBD2: %s wants too many credits (%d > %d)\n", >>> - current->comm, nblocks, >>> - journal->j_max_transaction_buffers); >>> + current->comm, blocks, >>> + journal->j_max_transaction_buffers / 2); >>> return -ENOSPC; >>> } >>> >>> so it's clear why the behavior changed, I guess, but it feels like I >>> must be missing something here. >> >> Is there some way to reserve these journal blocks only in the case of >> delalloc usage? This has caused a performance regression with Lustre >> servers on 3.10 kernels because the journal commits twice as often. >> We've worked around this for now by doubling the journal size, but it >> seems a bit of a hack since we can never use the whole journal anymore. > Hum, so the above hunk only limits maximum number of credits used by a > single handle. Multiple handles can still consume upto maximum transaction > size buffers (at least that's the intention :). So I don't see how that can > cause the problem you describe. What can happen though is that there are > quite a few outstanding reserved handles and so we have to reserve space > for them in the running transaction. Do you use dioread_nolock option? That > enables the use of reserved handles in ext4 for conversion of unwritten > extents... You're probably asking Andreas, but just in case, for my testcase, it's all defaults & standard options. i.e. just this fails, after the above commit, whereas it worked before. mkfs.ext4 /dev/sda 20M mount /dev/sda /mnt/test resize2fs /dev/sda 200M -Eric