mirror of
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
synced 2026-05-02 13:23:35 -04:00
0a2d82946b
Readahead support for IOCB_NOWAIT was introduced in commit2e85abf053("mm: allow read-ahead with IOCB_NOWAIT set"). However, this implementation broke the semantics of IOCB_NOWAIT by potentially causing it to wait on I/O during memory reclamation. This behavior was later modified in commitefa8480a83("fs: RWF_NOWAIT should imply IOCB_NOIO"). To resolve the blocking issue during memory reclamation, we can use memalloc_noio_{save,restore} to ensure non-blocking behavior. This change restores the original functionality, allowing preadv2(IOCB_NOWAIT) to trigger readahead if the file content is not present in the page cache. While this process may trigger direct memory reclamation, the __GFP_NORETRY flag is set in the readahead GFP flags, ensuring it won't block. A use case for this change is when we want to trigger readahead in the preadv2(2) syscall if the file cache is absent, but without waiting for certain filesystem locks, like xfs_ilock. A simple example is as follows: retry: if (preadv2(fd, iovec, cnt, offset, RWF_NOWAIT) < 0) { do_other_work(); goto retry; } Link: https://lore.gnuweeb.org/io-uring/20200624164127.GP21350@casper.infradead.org/ Link: https://lkml.kernel.org/r/20240820022639.89562-1-laoar.shao@gmail.com Signed-off-by: Yafang Shao <laoar.shao@gmail.com> Cc: Jens Axboe <axboe@kernel.dk> Cc: Matthew Wilcox <willy@infradead.org> Cc: Dave Chinner <david@fromorbit.com> Cc: Jan Kara <jack@suse.cz> Cc: Christian Brauner <brauner@kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
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 reStructuredText 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.