On Mon, Mar 16, 2015 at 03:34:12PM -0600, Andreas Dilger wrote:
> I wonder if something more lightweight could be added to avoid this
> problem? For example, we only care about this case if it has been
> going on for more than the lazytime interval (about a day), so the
> inode could store a 16-bit i_dirtied_time_when that is approximately
> (jiffies >> bits_in_a_half_a_day) and only check time_after() that.
> The __u16 could fit into some existing hole (e.g. after i_bytes on my
> kernel) and avoid expanding the size of the inode at all.
>
> The remaining high bits of i_dirtied_time_when would be irrelevant, since
> a __u16 of half-days is about 80 years, so it would be enough to compare:
>
>
> time_after(i_dirtied_time_when, (__u16)(jiffies >> bits_in_half_a_day))
That won't work correctly; we'd have to do something like this
#define u16_after(a,b) (typecheck(__u16, a) && typecheck(__u16, b) && \
((__s16)((b) - (a)) < 0))
> Minor issue, is there a good reason why dirtied_time_when doesn't have an
> "i_" prefix?
It's because dirtied_when also doesn't have an i_ prefix, but arguably
it should.
- Ted
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