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Diffstat (limited to 'Documentation/filesystems/ext4/orphan.rst')
| -rw-r--r-- | Documentation/filesystems/ext4/orphan.rst | 44 |
1 files changed, 17 insertions, 27 deletions
diff --git a/Documentation/filesystems/ext4/orphan.rst b/Documentation/filesystems/ext4/orphan.rst index bb19ecd1b626..03cca178864b 100644 --- a/Documentation/filesystems/ext4/orphan.rst +++ b/Documentation/filesystems/ext4/orphan.rst @@ -12,41 +12,31 @@ track the inode as orphan so that in case of crash extra blocks allocated to the file get truncated. Traditionally ext4 tracks orphan inodes in a form of single linked list where -superblock contains the inode number of the last orphan inode (s\_last\_orphan +superblock contains the inode number of the last orphan inode (s_last_orphan field) and then each inode contains inode number of the previously orphaned -inode (we overload i\_dtime inode field for this). However this filesystem +inode (we overload i_dtime inode field for this). However this filesystem global single linked list is a scalability bottleneck for workloads that result in heavy creation of orphan inodes. When orphan file feature -(COMPAT\_ORPHAN\_FILE) is enabled, the filesystem has a special inode -(referenced from the superblock through s\_orphan_file_inum) with several +(COMPAT_ORPHAN_FILE) is enabled, the filesystem has a special inode +(referenced from the superblock through s_orphan_file_inum) with several blocks. Each of these blocks has a structure: -.. list-table:: - :widths: 8 8 24 40 - :header-rows: 1 - - * - Offset - - Type - - Name - - Description - * - 0x0 - - Array of \_\_le32 entries - - Orphan inode entries - - Each \_\_le32 entry is either empty (0) or it contains inode number of - an orphan inode. - * - blocksize - 8 - - \_\_le32 - - ob\_magic - - Magic value stored in orphan block tail (0x0b10ca04) - * - blocksize - 4 - - \_\_le32 - - ob\_checksum - - Checksum of the orphan block. +============= ================ =============== =============================== +Offset Type Name Description +============= ================ =============== =============================== +0x0 Array of Orphan inode Each __le32 entry is either + __le32 entries entries empty (0) or it contains + inode number of an orphan + inode. +blocksize-8 __le32 ob_magic Magic value stored in orphan + block tail (0x0b10ca04) +blocksize-4 __le32 ob_checksum Checksum of the orphan block. +============= ================ =============== =============================== When a filesystem with orphan file feature is writeably mounted, we set -RO\_COMPAT\_ORPHAN\_PRESENT feature in the superblock to indicate there may +RO_COMPAT_ORPHAN_PRESENT feature in the superblock to indicate there may be valid orphan entries. In case we see this feature when mounting the filesystem, we read the whole orphan file and process all orphan inodes found there as usual. When cleanly unmounting the filesystem we remove the -RO\_COMPAT\_ORPHAN\_PRESENT feature to avoid unnecessary scanning of the orphan +RO_COMPAT_ORPHAN_PRESENT feature to avoid unnecessary scanning of the orphan file and also make the filesystem fully compatible with older kernels. |