Re: [PATCH 00/23] per device dirty throttling -v8

[Ingo Molnar <mingo@elte.hu>]

* Linus Torvalds <torvalds@linux-foundation.org> wrote:

> Well, we could make it the default for the kernel (possibly under a 
> "fast-atime" config option), and then people can add "atime" or 
> "noatime" as they wish, since mount has supported _those_ options for 
> a long time.

the patch below implements this, but there's a problem: we only have 
MNT_NOATIME, we have no MNT_ATIME option AFAICS. So there's no good way 
to detect it when a user _does_ want to have atime :-( Perhaps a boot 
option to turn this off? [sucks a bit but keeps the solution within the 
kernel.]

	Ingo

--------------------------------->
Subject: [patch] add CONFIG_FASTATIME
From: Ingo Molnar <mingo@elte.hu>

add the CONFIG_FASTATIME kernel option, which makes "relatime" the
default for all mounts.

Signed-off-by: Ingo Molnar <mingo@elte.hu>
---
 fs/Kconfig     |   10 ++++++++++
 fs/namespace.c |    4 ++++
 2 files changed, 14 insertions(+)

Index: linux/fs/Kconfig
===================================================================
--- linux.orig/fs/Kconfig
+++ linux/fs/Kconfig
@@ -2060,6 +2060,16 @@ config 9P_FS
 
 endmenu
 
+config FASTATIME
+	bool "Fast atime support by default"
+	default y
+	help
+	  If you say Y here, all your filesystems that do not have
+	  the "noatime" or "atime" mount option specified will get
+	  the "relatime" option by default, which speeds up atime
+	  updates. (atime will only be updated if ctime or mtime
+	  is more recent than atime)
+
 if BLOCK
 menu "Partition Types"
 
Index: linux/fs/namespace.c
===================================================================
--- linux.orig/fs/namespace.c
+++ linux/fs/namespace.c
@@ -1409,6 +1409,10 @@ long do_mount(char *dev_name, char *dir_
 		mnt_flags |= MNT_NODIRATIME;
 	if (flags & MS_RELATIME)
 		mnt_flags |= MNT_RELATIME;
+#ifdef CONFIG_FASTATIME
+	if (!(flags & (MNT_NOATIME | MNT_NODIRATIME)))
+		mnt_flags |= MNT_RELATIME;
+#endif
 
 	flags &= ~(MS_NOSUID | MS_NOEXEC | MS_NODEV | MS_ACTIVE |
 		   MS_NOATIME | MS_NODIRATIME | MS_RELATIME);
-
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