Hi Jan:
On Mon, Aug 15, 2011 at 8:03 AM, Jan Kara <jack@xxxxxxx> wrote:
> On Fri 12-08-11 15:47:25, Curt Wohlgemuth wrote:
>> Add a new file, /proc/writeback/stats, which displays
>> machine global data for how many pages were cleaned for
>> which reasons. It also displays some additional counts for
>> various writeback events.
>>
>> These data are also available for each BDI, in
>> /sys/block/<device>/bdi/writeback_stats .
> I think /sys/kernel/debug/bdi/<device>/writeback_stats might be a better
> place since we don't really want to make a stable interface out of this,
> do we?
Okay, I was waiting for someone to request this, I'll change it.
>> Sample output:
>>
>> page: balance_dirty_pages 2561544
>> page: background_writeout 5153
>> page: try_to_free_pages 0
>> page: sync 0
>> page: kupdate 102723
>> page: fdatawrite 1228779
>> page: laptop_periodic 0
>> page: free_more_memory 0
>> page: fs_free_space 0
> The above stats are probably useful. I'm not so convinced about the stats
> below - it looks like it should be simple enough to get them by enabling
> some trace points and processing output (or if we are missing some
> tracepoints, it would be worthwhile to add them).
For these specifically, I'd agree with you. In general, though, I
think that having generally available aggregated stats is really
useful, in a different way than tracepoints are.
>
>> periodic writeback 377
>> single inode wait 0
>> writeback_wb wait 1
>>
>> Signed-off-by: Curt Wohlgemuth <curtw@xxxxxxxxxx>
> ...
>> +static size_t writeback_stats_to_str(struct writeback_stats *stats,
>> + char *buf, size_t len)
>> +{
>> + int bufsize = len - 1;
>> + int i, printed = 0;
>> + for (i = 0; i < WB_STAT_MAX; i++) {
>> + const char *label = wb_stats_labels[i];
>> + if (label == NULL)
>> + continue;
>> + printed += snprintf(buf + printed, bufsize - printed,
>> + "%-32s %10llu\n", label, stats->stats[i]);
> Cast stats->stats[i] to unsigned long long explicitely since it doesn't
> have to be u64...
Thanks.
>> + if (printed >= bufsize) {
>> + buf[len - 1] = '\n';
>> + return len;
>> + }
>> + }
>> +
>> + buf[printed - 1] = '\n';
>> + return printed;
>> +}
>> +
>> +static int writeback_seq_show(struct seq_file *m, void *data)
>> +{
>> + char *buf;
>> + size_t size;
>> + switch ((enum writeback_op)m->private) {
>> + case WB_STATS_OP:
> What's the point of WB_STATS_OP?
It's a vestige of the many more files under /proc/writeback/ that we
have in our kernels (see my response to Fengguang's email) -- and so
processing each file is done via a different WB_xxx_OP. I forgot to
simplify this in the patch I sent out; will fix this.
>
>> + size = seq_get_buf(m, &buf);
>> + if (size == 0)
>> + return 0;
>> + size = writeback_stats_print(writeback_sys_stats, buf, size);
>> + seq_commit(m, size);
>> + break;
>> + default:
>> + break;
>> + }
>> +
>> + return 0;
>> +}
>> +
>> +static int writeback_open(struct inode *inode, struct file *file)
>> +{
>> + return single_open(file, writeback_seq_show, PDE(inode)->data);
>> +}
>> +
>> +static const struct file_operations writeback_ops = {
>> + .open = writeback_open,
>> + .read = seq_read,
>> + .llseek = seq_lseek,
>> + .release = single_release,
>> +};
>> +
>> +
>> +void __init proc_writeback_init(void)
>> +{
>> + struct proc_dir_entry *base_dir;
>> + base_dir = proc_mkdir("writeback", NULL);
>> + if (base_dir == NULL) {
>> + printk(KERN_ERR "Creating /proc/writeback/ failed");
>> + return;
>> + }
>> +
>> + writeback_sys_stats = alloc_percpu(struct writeback_stats);
>> +
>> + proc_create_data("stats", S_IRUGO|S_IWUSR, base_dir,
> Can user really write to the file?
No to this file, I'll fix, thanks. (Yes to some of our
/proc/writeback/ files, to clear them.)
Thanks,
Curt
>
>> + &writeback_ops, (void *)WB_STATS_OP);
>> +}
>
> Honza
> --
> Jan Kara <jack@xxxxxxx>
> SUSE Labs, CR
>
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