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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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