From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.2 (2018-09-13) on archive.lwn.net X-Spam-Level: X-Spam-Status: No, score=-5.7 required=5.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,RCVD_IN_DNSWL_HI,SPF_HELO_NONE,SPF_NONE autolearn=ham autolearn_force=no version=3.4.2 Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by archive.lwn.net (Postfix) with ESMTP id 663BE7D90F for ; Thu, 31 Oct 2019 06:55:18 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726911AbfJaGzP (ORCPT ); Thu, 31 Oct 2019 02:55:15 -0400 Received: from szxga05-in.huawei.com ([45.249.212.191]:5235 "EHLO huawei.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1726479AbfJaGzP (ORCPT ); Thu, 31 Oct 2019 02:55:15 -0400 Received: from DGGEMS402-HUB.china.huawei.com (unknown [172.30.72.58]) by Forcepoint Email with ESMTP id E01DC2C04A56620C2F94; Thu, 31 Oct 2019 14:55:12 +0800 (CST) Received: from [10.134.22.195] (10.134.22.195) by smtp.huawei.com (10.3.19.202) with Microsoft SMTP Server (TLS) id 14.3.439.0; Thu, 31 Oct 2019 14:55:07 +0800 Subject: Re: [f2fs-dev] [PATCH] f2fs: bio_alloc should never fail To: Jaegeuk Kim , "Theodore Y. Ts'o" CC: Jonathan Corbet , , Gao Xiang , , References: <20191030035518.65477-1-gaoxiang25@huawei.com> <20aa40bd-280d-d223-9f73-d9ed7dbe4f29@huawei.com> <20191030091542.GA24976@architecture4> <19a417e6-8f0e-564e-bc36-59bfc883ec16@huawei.com> <20191030104345.GB170703@architecture4> <20191030151444.GC16197@mit.edu> <20191030155020.GA3953@hsiangkao-HP-ZHAN-66-Pro-G1> <20191030162243.GA18729@mit.edu> <20191030163313.GB34056@jaegeuk-macbookpro.roam.corp.google.com> From: Chao Yu Message-ID: <0ef44e01-13a6-2519-bce2-075ca14a0cb9@huawei.com> Date: Thu, 31 Oct 2019 14:55:06 +0800 User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:52.0) Gecko/20100101 Thunderbird/52.9.1 MIME-Version: 1.0 In-Reply-To: <20191030163313.GB34056@jaegeuk-macbookpro.roam.corp.google.com> Content-Type: text/plain; charset="windows-1252" Content-Language: en-US Content-Transfer-Encoding: 7bit X-Originating-IP: [10.134.22.195] X-CFilter-Loop: Reflected Sender: linux-doc-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-doc@vger.kernel.org On 2019/10/31 0:33, Jaegeuk Kim wrote: > On 10/30, Theodore Y. Ts'o wrote: >> On Wed, Oct 30, 2019 at 11:50:37PM +0800, Gao Xiang wrote: >>> >>> So I'm curious about the original issue in commit 740432f83560 >>> ("f2fs: handle failed bio allocation"). Since f2fs manages multiple write >>> bios with its internal fio but it seems the commit is not helpful to >>> resolve potential mempool deadlock (I'm confused since no calltrace, >>> maybe I'm wrong)... >> >> Two possibilities come to mind. (a) It may be that on older kernels >> (when f2fs is backported to older Board Support Package kernels from >> the SOC vendors) didn't have the bio_alloc() guarantee, so it was >> necessary on older kernels, but not on upstream, or (b) it wasn't >> *actually* possible for bio_alloc() to fail and someone added the >> error handling in 740432f83560 out of paranoia. > > Yup, I was checking old device kernels but just stopped digging it out. > Instead, I hesitate to apply this patch since I can't get why we need to > get rid of this code for clean-up purpose. This may be able to bring > some hassles when backporting to android/device kernels. Jaegeuk, IIUC, as getting hint from commit 740432f83560, are we trying to fix potential deadlock like this? In low memory scenario: - f2fs_write_checkpoint() - block_operations() - f2fs_sync_node_pages() step 1) flush cold nodes, allocate new bio from mempool - bio_alloc() - mempool_alloc() step 2) flush hot nodes, allocate a bio from mempool - bio_alloc() - mempool_alloc() step 3) flush warm nodes, be stuck in below call path - bio_alloc() - mempool_alloc() - loop to wait mempool element release, as we only reserved memory for two bio allocation, however above allocated two bios never getting submitted. #define BIO_POOL_SIZE 2 If so, we need avoid using bioset, or introducing private bioset, at least enlarging mempool size to three (adapt to total log headers' number)... Thanks, > >> >> (Hence my suggestion that in the ext4 version of the patch, we add a >> code comment justifying why there was no error checking, to make it >> clear that this was a deliberate choice. :-) >> >> - Ted > > > _______________________________________________ > Linux-f2fs-devel mailing list > Linux-f2fs-devel@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/linux-f2fs-devel > . >