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imf12.hostedemail.com; dkim=none; dmarc=none; spf=pass (imf12.hostedemail.com: domain of yi.zhang@huaweicloud.com designates 45.249.212.51 as permitted sender) smtp.mailfrom=yi.zhang@huaweicloud.com ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1715000733; a=rsa-sha256; cv=none; b=TsSEgr0+3EiUxRleXVfHY3B3JE1h40wGSzvJLb7hP174x0pGgHgIcEdUmolZ1NbTKdHFRg HR1k4i0A+XDFie0wOewftSLCTQT74I4so57DP9D82bMmqxwjD63298v8IbUoYgAm9dXH/U c+SnYLp3sMYFT95neOcy62x1uFtIqYA= Received: from mail.maildlp.com (unknown [172.19.163.235]) by dggsgout11.his.huawei.com (SkyGuard) with ESMTP id 4VY1q33bFBz4f3l8W for ; Mon, 6 May 2024 21:05:19 +0800 (CST) Received: from mail02.huawei.com (unknown [10.116.40.75]) by mail.maildlp.com (Postfix) with ESMTP id BC33D1A0568 for ; Mon, 6 May 2024 21:05:24 +0800 (CST) Received: from [10.174.179.80] (unknown [10.174.179.80]) by APP2 (Coremail) with SMTP id Syh0CgAnmAuS1ThmXifRMA--.45497S3; Mon, 06 May 2024 21:05:24 +0800 (CST) Subject: Re: [RFC PATCH v4 29/34] ext4: fall back to buffer_head path for defrag To: Dave Chinner Cc: linux-ext4@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, tytso@mit.edu, adilger.kernel@dilger.ca, jack@suse.cz, ritesh.list@gmail.com, hch@infradead.org, djwong@kernel.org, willy@infradead.org, zokeefe@google.com, yi.zhang@huawei.com, chengzhihao1@huawei.com, yukuai3@huawei.com, wangkefeng.wang@huawei.com References: <20240410142948.2817554-1-yi.zhang@huaweicloud.com> <20240410150313.2820364-1-yi.zhang@huaweicloud.com> From: Zhang Yi Message-ID: <5dbb3021-b92e-2e53-7eee-5a6595a5ad03@huaweicloud.com> Date: Mon, 6 May 2024 21:05:22 +0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; 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Changing >> active inode is dangerous, before we start, we must hold the inode lock >> and the mapping->invalidate_lock, and writeback all dirty folios and >> drop the inode's pagecache. > > Even then, I don't think this is obviously safe. We went through > this with DAX and we couldn't make it work safely. > > Just return EOPNOTSUPP to the online defrag ioctl if iomap is in use > - that avoids all the excitement involved in doing dangerous things > like swapping aops structures on actively referenced inodes... > Okay, this is just a temporary solution to support defrag. I've been looking at how to support defrag for iomap recently, I hope it could be supported in the near future, so let's drop this dangerous operation. Thanks, Yi.