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David Disseldorp 1274aea127 initramfs: add INITRAMFS_PRESERVE_MTIME Kconfig option 
initramfs cpio mtime preservation, as implemented in commit 889d51a107
("initramfs: add option to preserve mtime from initramfs cpio images"),
uses a linked list to defer directory mtime processing until after all
other items in the cpio archive have been processed.  This is done to
ensure that parent directory mtimes aren't overwritten via subsequent
child creation.

The lkml link below indicates that the mtime retention use case was for
embedded devices with applications running exclusively out of initramfs,
where the 32-bit mtime value provided a rough file version identifier. 
Linux distributions which discard an extracted initramfs immediately after
the root filesystem has been mounted may want to avoid the unnecessary
overhead.

This change adds a new INITRAMFS_PRESERVE_MTIME Kconfig option, which can
be used to disable on-by-default mtime retention and in turn speed up
initramfs extraction, particularly for cpio archives with large directory
counts.

Benchmarks with a one million directory cpio archive extracted 20 times
demonstrated:
				mean extraction time (s)	std dev
INITRAMFS_PRESERVE_MTIME=y		3.808			 0.006
INITRAMFS_PRESERVE_MTIME unset		3.056			 0.004

The above extraction times were measured using ftrace (initcall_finish -
initcall_start) values for populate_rootfs() with initramfs_async
disabled.

[ddiss@suse.de: rebase atop dir_entry.name flexible array member and drop separate initramfs_mtime.h header]
Link: https://lkml.org/lkml/2008/9/3/424
Link: https://lkml.kernel.org/r/20220404093429.27570-4-ddiss@suse.de
Signed-off-by: David Disseldorp <ddiss@suse.de>
Reviewed-by: Martin Wilck <mwilck@suse.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Christian Brauner <christian.brauner@ubuntu.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
2022-05-09 18:29:19 -07:00
arch net: unexport csum_and_copy_{from,to}_user 2022-04-29 14:37:59 -07:00
block block: don't print I/O error warning for dead disks 2022-04-15 06:33:03 -06:00
certs Kbuild updates for v5.18 2022-03-31 11:59:03 -07:00
crypto for-5.18/64bit-pi-2022-03-25 2022-03-26 12:01:35 -07:00
Documentation Networking fixes for 5.18-rc5, including fixes from bluetooth, bpf 2022-04-28 12:34:50 -07:00
drivers rapidio: remove unnecessary use of list iterator 2022-04-29 14:38:03 -07:00
fs proc: fix dentry/inode overinstantiating under /proc/${pid}/net 2022-05-09 18:29:19 -07:00
include taskstats: version 12 with thread group and exe info 2022-04-29 14:38:03 -07:00
init initramfs: add INITRAMFS_PRESERVE_MTIME Kconfig option 2022-05-09 18:29:19 -07:00
ipc fs: allocate inode by using alloc_inode_sb() 2022-03-22 15:57:03 -07:00
kernel kernel: make taskstats available from all net namespaces 2022-04-29 14:38:03 -07:00
lib lib: remove back_str initialization 2022-04-29 14:38:01 -07:00
LICENSES LICENSES/LGPL-2.1: Add LGPL-2.1-or-later as valid identifiers 2021-12-16 14:33:10 +01:00
mm kasan: prevent cpu_quarantine corruption when CPU offline and cache shrink occur at same time 2022-04-27 13:28:48 -07:00
net tcp: fix F-RTO may not work correctly when receiving DSACK 2022-04-28 10:35:38 -07:00
samples dma-mapping updates for Linux 5.18 2022-03-29 08:50:14 -07:00
scripts get_maintainer: Honor mailmap for in file emails 2022-04-29 14:38:00 -07:00
security hardening updates for v5.18-rc1-fix1 2022-03-31 11:43:01 -07:00
sound ALSA: hda/realtek: Add quirk for Clevo NP70PNP 2022-04-21 21:23:47 +02:00
tools taskstats: version 12 with thread group and exe info 2022-04-29 14:38:03 -07:00
usr Kbuild updates for v5.18 2022-03-31 11:59:03 -07:00
virt KVM: SEV: add cache flush to solve SEV cache incoherency issues 2022-04-21 15:41:00 -04:00
.clang-format genirq/msi: Make interrupt allocation less convoluted 2021-12-16 22:22:20 +01:00
.cocciconfig
.get_maintainer.ignore Opt out of scripts/get_maintainer.pl 2019-05-16 10:53:40 -07:00
.gitattributes .gitattributes: use 'dts' diff driver for dts files 2019-12-04 19:44:11 -08:00
.gitignore .gitignore: ignore only top-level modules.builtin 2021-05-02 00:43:35 +09:00
.mailmap mailmap: update Vasily Averin's email address 2022-04-08 14:20:36 -10:00
COPYING COPYING: state that all contributions really are covered by this file 2020-02-10 13:32:20 -08:00
CREDITS MAINTAINERS: replace a Microchip AT91 maintainer 2022-02-09 11:30:01 +01:00
Kbuild kbuild: rename hostprogs-y/always to hostprogs/always-y 2020-02-04 01:53:07 +09:00
Kconfig kbuild: ensure full rebuild when the compiler is updated 2020-05-12 13:28:33 +09:00
MAINTAINERS MAINTAINERS: remove redundant file of PTRACE SUPPORT entry 2022-04-29 14:38:03 -07:00
Makefile Linux 5.18-rc4 2022-04-24 14:51:22 -07:00
README Drop all 00-INDEX files from Documentation/ 2018-09-09 15:08:58 -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 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.