From 1211121f0e73b44fe1c6df23ffdc1e3c7c7e6152 Mon Sep 17 00:00:00 2001 From: Jinke Han Date: Sat, 3 Sep 2022 09:24:29 +0800 Subject: [PATCH] ext4: place buffer head allocation before handle start commit d1052d236eddf6aa851434db1897b942e8db9921 upstream. In our product environment, we encounter some jbd hung waiting handles to stop while several writters were doing memory reclaim for buffer head allocation in delay alloc write path. Ext4 do buffer head allocation with holding transaction handle which may be blocked too long if the reclaim works not so smooth. According to our bcc trace, the reclaim time in buffer head allocation can reach 258s and the jbd transaction commit also take almost the same time meanwhile. Except for these extreme cases, we often see several seconds delays for cgroup memory reclaim on our servers. This is more likely to happen considering docker environment. One thing to note, the allocation of buffer heads is as often as page allocation or more often when blocksize less than page size. Just like page cache allocation, we should also place the buffer head allocation before startting the handle. Cc: stable@kernel.org Signed-off-by: Jinke Han Link: https://lore.kernel.org/r/20220903012429.22555-1-hanjinke.666@bytedance.com Signed-off-by: Theodore Ts'o Signed-off-by: Greg Kroah-Hartman --- fs/ext4/inode.c | 7 +++++++ 1 file changed, 7 insertions(+) diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c index 22feae1d5f77..9f9135336a17 100644 --- a/fs/ext4/inode.c +++ b/fs/ext4/inode.c @@ -1317,6 +1317,13 @@ retry_grab: page = grab_cache_page_write_begin(mapping, index, flags); if (!page) return -ENOMEM; + /* + * The same as page allocation, we prealloc buffer heads before + * starting the handle. + */ + if (!page_has_buffers(page)) + create_empty_buffers(page, inode->i_sb->s_blocksize, 0); + unlock_page(page); retry_journal: