On Thu, Dec 29, 2011 at 12:02:48PM +0800, Li Zefan wrote: > Martin Steigerwald wrote: > > Hi! > > > > With 3.2-rc4 (probably earlier), Ext4 seems to remember what areas it > > trimmed: > > > > merkaba:~> fstrim -v /boot > > /boot: 224657408 bytes were trimmed > > merkaba:~> fstrim -v /boot > > /boot: 0 bytes were trimmed > > > > > > But BTRFS does not: > > > > merkaba:~> fstrim -v / > > /: 4431613952 bytes were trimmed > > merkaba:~> fstrim -v / > > /: 4341846016 bytes were trimmed > > > > > > Is it planned to add this feature to BTRFS as well? > > > > There's no such plan, but it's do-able, and I can take care of it. > There's an issue though. > > Whether we want to store TRIMMED information on disk? ext4 doesn't > do this, so the first fstrim will be slow though you've done fstrim > in previous mount. I'd rather not store the trim status on disk. The extra trims don't have a huge cost, and since some devices have a large granularity for trims, they may ignore the trim until it tosses a larger contiguous area of the disk. I'd be fine with a flag to the in-memory free extent struct that indicates if it has been trimmed down to the device. -chris -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
