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Mon, 28 Sep 2026 04:57:42 -0700 (PDT) Received: from [100.125.248.95] ([124.70.231.46]) by smtp.gmail.com with ESMTPSA id 98e67ed59e1d1-3a0b99e5711sm19979522a91.17.2026.09.28.04.57.28 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 28 Sep 2026 04:57:42 -0700 (PDT) Message-ID: <214177f4-11d1-47f9-94fc-2fc679911b13@gmail.com> Date: Mon, 28 Sep 2026 19:57:26 +0800 Precedence: bulk X-Mailing-List: linux-ext4@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v6 08/31] ext4: avoid unnecessary transaction in ext4_map_blocks() for unwritten extents To: Ojaswin Mujoo , Zhang Yi Cc: linux-ext4@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, tytso@mit.edu, adilger.kernel@dilger.ca, libaokun@linux.alibaba.com, jack@suse.cz, ritesh.list@gmail.com, djwong@kernel.org, hch@infradead.org, yi.zhang@huawei.com, chengzhihao1@huawei.com, yangerkun@huawei.com, wangkefeng.wang@huawei.com, yukuai@fnnas.com References: <20260903123543.2302999-1-yi.zhang@huaweicloud.com> <20260903123543.2302999-9-yi.zhang@huaweicloud.com> Content-Language: en-US From: Zhang Yi In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 9/28/2026 6:21 PM, Ojaswin Mujoo wrote: > On Thu, Sep 03, 2026 at 08:35:20PM +0800, Zhang Yi wrote: >> From: Zhang Yi >> >> When ext4_map_blocks() finds an unwritten extent in the extent cache and >> the caller is willing to accept unwritten extents without conversion, >> there is no need to start a journal transaction since no metadata update >> is required. This avoids unnecessary transaction overhead in the >> upcoming iomap writeback path when overwriting already-allocated >> unwritten extents. >> >> One thing to be careful about, as the comment in ext4_map_blocks() >> states, if the flags contain EXT4_GET_BLOCKS_CREATE, the function will >> mark @map as mapped. >> >> Signed-off-by: Zhang Yi > > Yeahh, I had something similar in one of my WIP branches :) > > Thanks for taking care of this. Feel free to add: > > Reviewed-by: Ojaswin Mujoo > > Regards, > ojaswin Hi ojaswin, Thank you for the review! The fast path implemented in the current version is missing check_block_validity(), I'll add it in the next iteration. Thanks, Yi. > >> --- >> fs/ext4/inode.c | 19 ++++++++++++++----- >> 1 file changed, 14 insertions(+), 5 deletions(-) >> >> diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c >> index c9dea4ca5caf..7a5c74af8ff3 100644 >> --- a/fs/ext4/inode.c >> +++ b/fs/ext4/inode.c >> @@ -809,14 +809,23 @@ int ext4_map_blocks(handle_t *handle, struct inode *inode, >> * Note that if blocks have been preallocated >> * ext4_ext_map_blocks() returns with buffer head unmapped >> */ >> - if (retval > 0 && map->m_flags & EXT4_MAP_MAPPED) >> + if (retval > 0) { >> /* >> - * If we need to convert extent to unwritten >> - * we continue and do the actual work in >> - * ext4_ext_map_blocks() >> + * If we need to convert written extent to unwritten or >> + * convert unwritten extent to written, continue and do >> + * the actual work in ext4_ext_map_blocks(). >> */ >> - if (!(flags & EXT4_GET_BLOCKS_CONVERT_UNWRITTEN)) >> + if (map->m_flags & EXT4_MAP_MAPPED && >> + !(flags & EXT4_GET_BLOCKS_CONVERT_UNWRITTEN)) >> goto out_handle; >> + if (map->m_flags & EXT4_MAP_UNWRITTEN && >> + (flags & EXT4_GET_BLOCKS_UNWRIT_EXT) && >> + !(flags & EXT4_GET_BLOCKS_CONVERT)) { >> + /* Contains EXT4_GET_BLOCKS_CREATE - mark mapped. */ >> + map->m_flags |= EXT4_MAP_MAPPED; >> + goto out_handle; >> + } >> + } >> >> if (!handle) { >> handle = ext4_journal_start(inode, EXT4_HT_MAP_BLOCKS, >> -- >> 2.52.0 >>