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Message-ID: <zqrcmug26tnhhjombztjjqwcorbnk4elqg2dqayhtfo2gkx3e3@wvzykthigny6> Date: Thu, 3 Jul 2025 18:27:26 +0200 From: Jan Kara <jack@...e.cz> To: Zhang Yi <yi.zhang@...weicloud.com> Cc: Jan Kara <jack@...e.cz>, 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 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. Honza -- Jan Kara <jack@...e.com> SUSE Labs, CR
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