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Yafang Shao 0a2d82946b mm: allow read-ahead with IOCB_NOWAIT set 
Readahead support for IOCB_NOWAIT was introduced in commit 2e85abf053
("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 commit efa8480a83 ("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>
2024-09-03 21:15:40 -07:00
arch mm: make range-to-target_node lookup facility a part of numa_memblks 2024-09-03 21:15:32 -07:00
block block: fix detection of unsupported WRITE SAME in blkdev_issue_write_zeroes 2024-08-28 08:49:25 -06:00
certs kbuild: use $(src) instead of $(srctree)/$(src) for source directory 2024-05-10 04:34:52 +09:00
crypto crypto: testmgr - generate power-of-2 lengths more often 2024-07-13 11:50:28 +12:00
Documentation mm,memcg: provide per-cgroup counters for NUMA balancing operations 2024-09-03 21:15:36 -07:00
drivers mm: make range-to-target_node lookup facility a part of numa_memblks 2024-09-03 21:15:32 -07:00
fs mm: remove PG_error 2024-09-01 20:26:05 -07:00
include mm: allow read-ahead with IOCB_NOWAIT set 2024-09-03 21:15:40 -07:00
init mm: fix typo in Kconfig 2024-09-01 20:25:45 -07:00
io_uring io_uring/kbuf: return correct iovec count from classic buffer peek 2024-08-30 10:45:54 -06:00
ipc sysctl: treewide: constify the ctl_table argument of proc_handlers 2024-07-24 20:59:29 +02:00
kernel mm: move kernel/numa.c to mm/ 2024-09-03 21:15:26 -07:00
lib maple_tree: make write helper functions void 2024-09-01 20:26:18 -07:00
LICENSES LICENSES: Add the copyleft-next-0.3.1 license 2022-11-08 15:44:01 +01:00
mm mm: allow read-ahead with IOCB_NOWAIT set 2024-09-03 21:15:40 -07:00
net Including fixes from bluetooth, wireless and netfilter. 2024-08-30 06:14:39 +12:00
rust Rust fixes for v6.11 2024-08-16 11:24:06 -07:00
samples kmemleak-test: add percpu leak 2024-09-01 20:25:50 -07:00
scripts kasan: simplify and clarify Makefile 2024-09-03 21:15:35 -07:00
security Merge branch 'fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/groeck/linux-staging 2024-09-01 09:18:48 +12:00
sound sound fixes for 6.11-rc6 2024-08-28 06:24:22 +12:00
tools selftests: mm: support shmem mTHP collapse testing 2024-09-03 21:15:39 -07:00
usr initramfs: shorten cmd_initfs in usr/Makefile 2024-07-16 01:07:52 +09:00
virt KVM: x86: Disallow read-only memslots for SEV-ES and SEV-SNP (and TDX) 2024-08-14 12:28:24 -04:00
.clang-format Docs: Move clang-format from process/ to dev-tools/ 2024-06-26 16:36:00 -06:00
.cocciconfig
.editorconfig .editorconfig: remove trim_trailing_whitespace option 2024-06-13 16:47:52 +02:00
.get_maintainer.ignore Add Jeff Kirsher to .get_maintainer.ignore 2024-03-08 11:36:54 +00:00
.gitattributes .gitattributes: set diff driver for Rust source code files 2023-05-31 17:48:25 +02:00
.gitignore kbuild: add script and target to generate pacman package 2024-07-22 01:24:22 +09:00
.mailmap ARM: SoC fixes for 6.11, part 2 2024-09-01 06:42:13 +12:00
.rustfmt.toml rust: add .rustfmt.toml 2022-09-28 09:02:20 +02:00
COPYING
CREDITS tracing: Update of MAINTAINERS and CREDITS file 2024-07-18 14:08:42 -07:00
Kbuild Kbuild updates for v6.1 2022-10-10 12:00:45 -07:00
Kconfig
MAINTAINERS tools: add skeleton code for userland testing of VMA logic 2024-09-01 20:25:55 -07:00
Makefile Linux 6.11-rc6 2024-09-01 19:46:02 +12:00
README README: Fix spelling 2024-03-18 03:36:32 -06:00

README 

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.