Re: kernel 3.17-rc3: task rsync:2524 blocked for more than 120 seconds

[Duncan <1i5t5.duncan@cox.net>]

Chris Murphy posted on Tue, 02 Sep 2014 20:44:06 -0600 as excerpted:

> On Sep 2, 2014, at 12:40 AM, Duncan <1i5t5.duncan@cox.net> wrote:
>> 
>> Mkfs.btrfs used to default to 4 KiB node/leaf sizes; now days it
>> defaults to 16 KiB as that's far better for most usage.  I wonder if
>> USB sticks are an exception…
> 
> USB sticks > 1 GB get 16KB nodesize also.

Seems you read into that a meaning I didn't even consider when I wrote 
it. =:^/

I /meant/ that AFAIK mkfs.btrfs did the usual 16K thing, but that perhaps 
(some, depending on erase-block size) USB sticks are an exception to 16K 
being better than 4K thing.

> At <= 1 GB, mixed-bg is
> default as is 4KB nodesize. Probably because queue/rotational is 1 for
> USB sticks, they mount without ssd or ssd_spread which may be
> unfortunate (I haven't benchmarked it but I suspect ssd_spread would
> work well for USB sticks).

I did mention ssd_spread somewhere in my replies, due to the same 
suspicion.  Good to see you have the same suspicion I do. =:^)

> It was suggested a while ago that maybe mixed-bg should apply to larger
> volumes, maybe up to 8GB or 16GB?

Indeed.  Considering the default data chunk size is 1 GiB, that as the 
cutoff for default mixed-bg mode seems kinda low.  If anything, I think 
16 GiB is still a low cutoff value, at least as long as the only way to 
reclaim out-of-balance data/metadata assigned chunks is via a manual 
balance.  I'd suggest a 32 GiB cutover by default.

Tho if btrfs gets a good auto-balance-trigger mechanism that say triggers 
when allocated (fi show device figure) is within say 10% of total 
filesystem space (rounded up to the nearest GiB, minimum 2 GiB) AND data 
or metadata has more than say 10% spread between used and allocated (fi 
df, again rounded up, 2 GiB minimum), that can arguably come down a 
notch, to say 16 GiB.

-- 
Duncan - List replies preferred.   No HTML msgs.
"Every nonfree program has a lord, a master --
and if you use the program, he is your master."  Richard Stallman