linux-kernel - [PATCH 0/5] ext4: fix insufficient credits when writing back large folios

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Message-ID: <20250530062858.458039-1-yi.zhang@huaweicloud.com>
Date: Fri, 30 May 2025 14:28:53 +0800
From: Zhang Yi <yi.zhang@...weicloud.com>
To: linux-ext4@...r.kernel.org
Cc: linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	tytso@....edu,
	adilger.kernel@...ger.ca,
	jack@...e.cz,
	ojaswin@...ux.ibm.com,
	yi.zhang@...wei.com,
	yi.zhang@...weicloud.com,
	libaokun1@...wei.com,
	yukuai3@...wei.com,
	yangerkun@...wei.com
Subject: [PATCH 0/5] ext4: fix insufficient credits when writing back large folios

From: Zhang Yi <yi.zhang@...wei.com>

This series addresses the issue that Jan pointed out regarding large
folios support for ext4[1]. The problem is that the credits calculation
may insufficient in ext4_meta_trans_blocks() when allocating blocks
during write back a sufficiently large and discontinuous folio, it
doesn't involve the credits for updating bitmap and group descriptor
block. However, if we fix this issue, it may lead to significant
overestimation on the some filesystems with a lot of block groups.

The solution involves first reserving credit for one page when writing
back a sufficiently large and discontinuous folio, and then attempting
to extend the current transaction's credits. If the credits reach the
upper limit, the handler stops and initiates a new transaction. Again,
fix the wrong credits calculation in ext4_meta_trans_blocks(). Finally,
this solution only works in dioread_nolock mode, so disable large folios
if dioread_nolock is disabled. Please see the following patches for
details.

[1] https://lore.kernel.org/linux-ext4/ht54j6bvjmiqt62xmcveqlo7bmrunqs4ji7wikfteftdjijzek@7tz5gpejaoen/

Thanks,
Yi.

Zhang Yi (5):
  ext4: restart handle if credits are insufficient during writepages
  ext4: correct the reserved credits for extent conversion
  ext4/jbd2: reintroduce jbd2_journal_blocks_per_page()
  ext4: fix insufficient credits calculation in ext4_meta_trans_blocks()
  ext4: disable large folios if dioread_nolock is not enabled

 fs/ext4/ext4_jbd2.h  | 14 ++++++++++
 fs/ext4/inode.c      | 64 +++++++++++++++++++++++++++++++++++---------
 fs/jbd2/journal.c    |  6 +++++
 include/linux/jbd2.h |  1 +
 4 files changed, 72 insertions(+), 13 deletions(-)

-- 
2.46.1