Re: [PATCH 004 of 11] md: Increase the delay before marking metadata clean, and make it configurable.

Andrew Morton
2006-05-01T05:45:59Z

NeilBrown <neilb@suse.de> wrote:
>
>
> When a md array has been idle (no writes) for 20msecs it is marked as
> 'clean'. This delay turns out to be too short for some real
> workloads. So increase it to 200msec (the time to update the metadata
> should be a tiny fraction of that) and make it sysfs-configurable.
>
>
> ...
>
> + safe_mode_delay
> + When an md array has seen no write requests for a certain period
> + of time, it will be marked as 'clean'. When another write
> + request arrive, the array is marked as 'dirty' before the write
> + commenses. This is known as 'safe_mode'.
> + The 'certain period' is controlled by this file which stores the
> + period as a number of seconds. The default is 200msec (0.200).
> + Writing a value of 0 disables safemode.
> +

Why not make the units milliseconds? Rename this to safe_mode_delay_msecs
to remove any doubt.

> +static ssize_t
> +safe_delay_store(mddev_t *mddev, const char *cbuf, size_t len)
> +{
> + int scale=1;
> + int dot=0;
> + int i;
> + unsigned long msec;
> + char buf[30];
> + char *e;
> + /* remove a period, and count digits after it */
> + if (len >= sizeof(buf))
> + return -EINVAL;
> + strlcpy(buf, cbuf, len);
> + buf[len] = 0;
> + for (i=0; i<len; i++) {
> + if (dot) {
> + if (isdigit(buf[i])) {
> + buf[i-1] = buf[i];
> + scale *= 10;
> + }
> + buf[i] = 0;
> + } else if (buf[i] == '.') {
> + dot=1;
> + buf[i] = 0;
> + }
> + }
> + msec = simple_strtoul(buf, &e, 10);
> + if (e == buf || (*e && *e != '\n'))
> + return -EINVAL;
> + msec = (msec * 1000) / scale;
> + if (msec == 0)
> + mddev->safemode_delay = 0;
> + else {
> + mddev->safemode_delay = (msec*HZ)/1000;
> + if (mddev->safemode_delay == 0)
> + mddev->safemode_delay = 1;
> + }
> + return len;

And most of that goes away.