Holger Hoffstätte <holger.hoffstaette <at> googlemail.com> writes:
> > On 11/11/15 23:08, Holger Hoffstätte wrote: > > On 11/11/15 22:29, Jens Axboe wrote: > >> On 11/11/2015 08:21 AM, Holger Hoffstätte wrote: > >>> > >>> The loop driver always declares the rotational flag of its device as > >>> rotational, even when the device of the mapped file is nonrotational, > >>> as is the case with SSDs or on tmpfs. This can confuse filesystem tools > >>> which are SSD-aware; in my case I frequently forget to tell mkfs.btrfs > >>> that my loop device on tmpfs is nonrotational, and that I really don't > >>> need any automatic metadata redundancy. > >>> > >>> The attached patch fixes this by introspecting the rotational flag of the > >>> mapped file's underlying block device, if it exists. If the mapped file's > >>> filesystem has no associated block device - as is the case on e.g. tmpfs - > >>> we assume nonrotational storage. If there is a better way to identify such > >>> non-devices I'd love to hear them. > >>> > >>> Signed-off-by: Holger Hoffstätte <holger.hoffstaette <at> googlemail.com> > > Jens, > > I haven't seen this merged in any trees yet and was wondering if there's > any chance to get this into 4.5? If there's something left to fix up please > let me know. > > Thanks, > Holger > > This patch proved useful for ureadahead: when we use it on a loop device, it would use the HDD method to place the data in cache using the pack information instead of the SSD method. Signed-off-by: Gwendal Grignou <[email protected]>
