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Right now, discard is issued and waited to be completed in jbd2 commit kthread context after the logs are committed. When large amount of files are deleted and discard is flooding, jbd2 commit kthread can be blocked for long time. Then all of the metadata operations can be blocked to wait the log space. One case is the page fault path with read mm->mmap_sem held, which wants to update the file time but has to wait for the log space. When other threads in the task wants to do mmap, then write mmap_sem is blocked. Finally all of the following read mmap_sem requirements are blocked, even the ps command which need to read the /proc/pid/ -cmdline. Our monitor service which needs to read /proc/pid/cmdline used to be blocked for 5 mins. This patch frees the blocks back to buddy after commit and then do discard in a async kworker context in fstrim fashion, namely, - mark blocks to be discarded as used if they have not been allocated - do discard - mark them free After this, jbd2 commit kthread won't be blocked any more by discard and we won't get NOSPC even if the discard is slow or throttled. Link: https://marc.info/?l=linux-kernel&m=162143690731901&w=2 Suggested-by: Theodore Ts'o <tytso@mit.edu> Reviewed-by: Jan Kara <jack@suse.cz> Signed-off-by: Wang Jianchao <wangjianchao@kuaishou.com> Link: https://lore.kernel.org/r/20210830075246.12516-5-jianchao.wan9@gmail.com Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.