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
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calibrate.c
do_mounts_initrd.c	Merge branch 'hch.init_path' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs	2020-08-07 09:40:34 -07:00
do_mounts_rd.c	init: add an init_unlink helper	2020-07-31 08:17:52 +02:00
do_mounts.c	block: remove genhd.h	2022-02-02 07:49:59 -07:00
do_mounts.h	init: add an init_mknod helper	2020-07-31 08:17:54 +02:00
init_task.c	kcsan: Remove redundant zero-initialization of globals	2021-12-09 16:42:26 -08:00
initramfs.c	initramfs: add INITRAMFS_PRESERVE_MTIME Kconfig option	2022-05-09 18:29:19 -07:00
Kconfig	initramfs: add INITRAMFS_PRESERVE_MTIME Kconfig option	2022-05-09 18:29:19 -07:00
main.c	Merge branch 'akpm' (patches from Andrew)	2022-03-24 14:14:07 -07:00
Makefile	sched/preempt: Tell about PREEMPT_DYNAMIC on kernel headers	2022-03-11 15:36:35 +01:00
noinitramfs.c	init: move usermodehelper_enable() to populate_rootfs()	2021-09-08 11:50:27 -07:00
version.c	kbuild: add an elfnote for whether vmlinux is built with lto	2021-04-25 05:25:42 +09:00