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Message-ID: <6a47b6f2-08d5-49ae-aee5-9068a421de05@huaweicloud.com> Date: Fri, 4 Jul 2025 16:47:09 +0800 From: Zhang Yi <yi.zhang@...weicloud.com> To: Jan Kara <jack@...e.cz> Cc: linux-ext4@...r.kernel.org, linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org, tytso@....edu, adilger.kernel@...ger.ca, ojaswin@...ux.ibm.com, sashal@...nel.org, yi.zhang@...wei.com, libaokun1@...wei.com, yukuai3@...wei.com, yangerkun@...wei.com Subject: Re: [PATCH v3 05/10] ext4: restart handle if credits are insufficient during allocating blocks On 2025/7/4 16:18, Jan Kara wrote: > On Fri 04-07-25 09:40:23, Zhang Yi wrote: >> On 2025/7/4 0:27, Jan Kara wrote: >>> On Thu 03-07-25 10:13:07, Zhang Yi wrote: >>>> On 2025/7/2 22:18, Jan Kara wrote: >>>>> On Tue 01-07-25 21:06:30, Zhang Yi wrote: >>>>>> From: Zhang Yi <yi.zhang@...wei.com> >>>>>> >>>>>> After large folios are supported on ext4, writing back a sufficiently >>>>>> large and discontinuous folio may consume a significant number of >>>>>> journal credits, placing considerable strain on the journal. For >>>>>> example, in a 20GB filesystem with 1K block size and 1MB journal size, >>>>>> writing back a 2MB folio could require thousands of credits in the >>>>>> worst-case scenario (when each block is discontinuous and distributed >>>>>> across different block groups), potentially exceeding the journal size. >>>>>> This issue can also occur in ext4_write_begin() and ext4_page_mkwrite() >>>>>> when delalloc is not enabled. >>>>>> >>>>>> Fix this by ensuring that there are sufficient journal credits before >>>>>> allocating an extent in mpage_map_one_extent() and >>>>>> ext4_block_write_begin(). If there are not enough credits, return >>>>>> -EAGAIN, exit the current mapping loop, restart a new handle and a new >>>>>> transaction, and allocating blocks on this folio again in the next >>>>>> iteration. >>>>>> >>>>>> Suggested-by: Jan Kara <jack@...e.cz> >>>>>> Signed-off-by: Zhang Yi <yi.zhang@...wei.com> >>>>> >>>>> Very nice. Feel free to add: >>>>> >>>>> Reviewed-by: Jan Kara <jack@...e.cz> >>>>> >>>>> One small comment below: >>>>> >>>>>> +/* >>>>>> + * Make sure that the current journal transaction has enough credits to map >>>>>> + * one extent. Return -EAGAIN if it cannot extend the current running >>>>>> + * transaction. >>>>>> + */ >>>>>> +static inline int ext4_journal_ensure_extent_credits(handle_t *handle, >>>>>> + struct inode *inode) >>>>>> +{ >>>>>> + int credits; >>>>>> + int ret; >>>>>> + >>>>>> + if (!handle) >>>>> >>>>> Shouldn't this rather be ext4_handle_valid(handle) to catch nojournal mode >>>>> properly? >>>>> >>>> __ext4_journal_ensure_credits() already calls ext4_handle_valid() to handle >>>> nojournal mode, and the '!handle' check here is to handle the case where >>>> ext4_block_write_begin() passes in a NULL 'handle'. >>> >>> Ah, right. But then you don't need the test at all, do you? Anyway, >>> whatever you decide to do with this (or nothing) is fine by me. >>> >> >> Yeah, remove this test is fine with me. I added this one is because the >> comments in ext4_handle_valid() said "Do not use this for NULL handles." >> I think it is best to follow this rule. :) > > Right, I didn't read that comment :) So maybe the best fix will be just > adding a comment before the test like: > > /* Called from ext4_da_write_begin() which has no handle started? */ > if (!handle) > return 0; > Sure, it looks good, will do. Thanks, Yi.
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