> -----Original Message----- > From: Linux-nvdimm [mailto:linux-nvdimm-bounces@xxxxxxxxxxxx] On Behalf Of > Dan Williams > Sent: Wednesday, December 23, 2015 11:16 AM > To: Cholerae Hu <choleraehyq@xxxxxxxxx> > Cc: linux-nvdimm@xxxxxxxxxxxx > Subject: Re: A blocksize problem about dax and ext4 > > On Wed, Dec 23, 2015 at 4:03 AM, Cholerae Hu <choleraehyq@xxxxxxxxx> > wrote: ... > > [root@localhost cholerae]# mount -o dax /dev/pmem0 /mnt/mem > > mount: wrong fs type, bad option, bad superblock on /dev/pmem0, > > missing codepage or helper program, or other error > > > > In some cases useful info is found in syslog - try > > dmesg | tail or so. > > [root@localhost cholerae]# dmesg | tail ... > > [ 81.779582] EXT4-fs (pmem0): error: unsupported blocksize for dax ... > What's the fs block size? For example: > # dumpe2fs -h /dev/pmem0 | grep "Block size" > dumpe2fs 1.42.9 (28-Dec-2013) > Block size: 4096 > Depending on the size of /dev/pmem0 it may have automatically set it > to a block size less than 4 KiB which is incompatible with "-o dax". I noticed a few things while trying that out on both ext4 and xfs. $ sudo mkfs.ext4 -F -b 1024 /dev/pmem0 $ sudo mount -o dax /dev/pmem0 /mnt/ext4-pmem0 $ sudo mkfs.xfs -f -b size=1024 /dev/pmem0 $ sudo mount -o dax /dev/pmem0 /mnt/xfs-pmem0 [ 199.679195] EXT4-fs (pmem0): DAX enabled. Warning: EXPERIMENTAL, use at your own risk [ 199.724931] EXT4-fs (pmem0): error: unsupported block size 1024 for dax [ 859.077766] XFS (pmem0): DAX enabled. Warning: EXPERIMENTAL, use at your own risk [ 859.118106] XFS (pmem0): Filesystem block size invalid for DAX Turning DAX off. [ 859.156950] XFS (pmem0): Mounting V4 Filesystem [ 859.183626] XFS (pmem0): Ending clean mount 1. ext4 fails to mount the filesystem, while xfs just disables DAX. It seems like they should they be the same. 2. if CONFIG_FS_DAX is not supported, ext4 fails to mount, but prints the message at the KERN_INFO level. All the rest of its mount errors use KERN_ERR. Completely unknown mount options are reported like this at the KERN_ERR level: [ 2188.194775] EXT4-fs (pmem0): Unrecognized mount option "xyzzy" or missing value In contrast, if CONFIG_FS_DAX is not supported, then xfs lumps it in with the rest of the unknown mount options, which are reported with xfs_warn(): [ 2347.654182] XFS (pmem0): unknown mount option [xyzzy]. 3. It might be worth printing the problematic filesystem block size (here and in a few other similar messages). I like how xfs' wording of "Filesystem block size" helps distinguish the value from the block device's logical block size. Code excerpts ============= fs/xfs/xfs_super.c: #ifdef CONFIG_FS_DAX } else if (!strcmp(this_char, MNTOPT_DAX)) { mp->m_flags |= XFS_MOUNT_DAX; #endif ... if (mp->m_flags & XFS_MOUNT_DAX) { xfs_warn(mp, "DAX enabled. Warning: EXPERIMENTAL, use at your own risk"); if (sb->s_blocksize != PAGE_SIZE) { xfs_alert(mp, "Filesystem block size invalid for DAX Turning DAX off."); mp->m_flags &= ~XFS_MOUNT_DAX; } else if (!sb->s_bdev->bd_disk->fops->direct_access) { xfs_alert(mp, "Block device does not support DAX Turning DAX off."); mp->m_flags &= ~XFS_MOUNT_DAX; } } fs/ext4/super.c: } else if (token == Opt_dax) { #ifdef CONFIG_FS_DAX ext4_msg(sb, KERN_WARNING, "DAX enabled. Warning: EXPERIMENTAL, use at your own risk"); sbi->s_mount_opt |= m->mount_opt; #else ext4_msg(sb, KERN_INFO, "dax option not supported"); return -1; #endif --- Robert Elliott, HPE Persistent Memory -- 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
