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Message-ID: <ceb8c9c1-f426-4cd0-b7d8-841190631a90@huaweicloud.com> Date: Thu, 3 Jul 2025 10:13:07 +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 2025/7/2 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'. Thanks, Yi.
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