On Thu, 2013-09-12 at 10:18 -0500, Eric Sandeen wrote:
> On 9/12/13 9:54 AM, Calvin Walton wrote:
> > On Thu, 2013-09-12 at 16:18 +0200, Julian Andres Klode wrote:
> >> Hi,
> >>
> >> I installed my new laptop on Saturday and setup an ext4 filesystem
> >> on my / and /home partitions. Without me doing much file transfers,
> >> I noticed today:
> >>
> >> jak@jak-x230:~$ cat /sys/fs/ext4/sdb3/lifetime_write_kbytes
> >> 342614039
> >>
> >> This is on a 100GB partition. I used fstrim multiple times. I analysed
> >> the increase over some time today and issued an fstrim in between:
> > <snip>
> >> So it seems that ext4 counts the trims as writes? I don't know how I could
> >> get 300GB of writes on a 100GB partition -- of which only 8 GB are occupied
> >> -- otherwise.
> >
> > The way fstrim works is that it allocates a temporary file that fills
> > almost the entire free space on the partition.
>
> No, that's not correct.
> Nope. ;) strace it and see, it does nothing like this - it calls a special
> ioctl to ask the fs to find and issue discards on unused blocks.
>
> # strace -e open,write,fallocate,unlink,ioctl fstrim mnt/
> open("/etc/ld.so.cache", O_RDONLY) = 3
> open("/lib64/libc.so.6", O_RDONLY) = 3
> open("/usr/lib/locale/locale-archive", O_RDONLY) = 3
> open("mnt/", O_RDONLY) = 3
> ioctl(3, 0xc0185879, 0x7fff6ac47d40) = 0 <=== FITRIM ioctl
>
> (old hdparm discard might have done what you say, but that was a hack).
Alright, you got me there :) To be honest, I got the name 'fstrim'
confused with the old 'wiper.sh' script that used to be the only way to
do this, and did in fact function as I said.
Having this all integrated into the filesystem itself is quite a nice
change for the better - the old way was definitely a hack! I suppose
this was added sometime in the 2011 timeframe?
--
Calvin Walton <calvin.walton@xxxxxxxxxx>
--
To unsubscribe from this list: send the line "unsubscribe linux-ext4" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
