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SubjectRe: [PATCH 1/2] relatime: Make atime updates more useful
On Wed, 26 Nov 2008 19:54:57 +0000 Matthew Garrett <mjg59@srcf.ucam.org> wrote:
> Allow atime to be updated once per day even with relatime enabled. This
> lets utilities like tmpreaper (which deletes files based on last access
> time) continue working.
>
> Signed-off-by: Matthew Garrett <mjg@redhat.com>
>
> ---
>
> Updated version of Ingo's patch from last year - this section is
> identical.
>
> commit 2c145e187600ca961715fa82ae3ae7919d744bc9
> Author: Matthew Garrett <mjg@redhat.com>
> Date: Wed Nov 26 17:44:07 2008 +0000
>
> Make relatime smarter
>
> Allow atime to be updated once per day even with relatime. This lets
> utilities like tmpreaper (which delete files based on last access time)
> continue working.
>

Two changelogs always sends me into a panic. It's easier when they are
identical ;)

> index 0487ddb..348fa16 100644
> --- a/fs/inode.c
> +++ b/fs/inode.c
> @@ -1179,6 +1179,41 @@ sector_t bmap(struct inode * inode, sector_t block)
> }
> EXPORT_SYMBOL(bmap);
>
> +/*
> + * Relative atime updates frequency (default: 1 day):
> + */
> +int relatime_interval __read_mostly = 24*60*60;

I assume that it's global for the benefit of the second patch.

Yes, we do put a lot of extern-decls-in-C over in sysctl.c. But that
doesn't make it good. It would be better to add the declaration to a
header which is visible to all sites which use the symbol.

We should perhaps have a standalone sysctl-definitions.h for this
purpose, so we don't end up having to #include <everything> in
sysctl.c.

> +/*
> + * With relative atime, only update atime if the
> + * previous atime is earlier than either the ctime or
> + * mtime.
> + */
> +static int relatime_need_update(struct inode *inode, struct timespec now)
> +{
> + /*
> + * Is mtime younger than atime? If yes, update atime:
> + */
> + if (timespec_compare(&inode->i_mtime, &inode->i_atime) >= 0)
> + return 1;
> + /*
> + * Is ctime younger than atime? If yes, update atime:
> + */
> + if (timespec_compare(&inode->i_ctime, &inode->i_atime) >= 0)
> + return 1;
> +
> + /*
> + * Is the previous atime value older than the update interval?
> + * If yes, update atime:
> + */
> + if ((long)(now.tv_sec - inode->i_atime.tv_sec) >= relatime_interval)
> + return 1;

I dunno what type those tv_secs have, but the whole thing is cast to a
long and is then signed-compared with an integer.

Is this correct and intended? I guess it is, but.. just checking?

> + /*
> + * Good, we can skip the atime update:
> + */
> + return 0;
> +}
> +
> /**
> * touch_atime - update the access time
> * @mnt: mount the inode is accessed on
> @@ -1206,17 +1241,12 @@ void touch_atime(struct vfsmount *mnt, struct dentry *dentry)
> goto out;
> if ((mnt->mnt_flags & MNT_NODIRATIME) && S_ISDIR(inode->i_mode))
> goto out;
> - if (mnt->mnt_flags & MNT_RELATIME) {
> - /*
> - * With relative atime, only update atime if the previous
> - * atime is earlier than either the ctime or mtime.
> - */
> - if (timespec_compare(&inode->i_mtime, &inode->i_atime) < 0 &&
> - timespec_compare(&inode->i_ctime, &inode->i_atime) < 0)
> - goto out;
> - }
>
> now = current_fs_time(inode->i_sb);
> +
> + if (mnt->mnt_flags & MNT_RELATIME)
> + if (!relatime_need_update(inode, now))
> + goto out;
> if (timespec_equal(&inode->i_atime, &now))
> goto out;



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