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Message-Id: <1295365843-29414-1-git-send-email-lczerner@redhat.com> Date: Tue, 18 Jan 2011 16:50:43 +0100 From: Lukas Czerner <lczerner@...hat.com> To: linux-ext4@...r.kernel.org Cc: tytso@....edu, lczerner@...hat.com, sandeen@...hat.com Subject: [PATCH] Ext4: Update ext4 documentation Since Documentation/filesystem/ext4.txt has not been updated for a while, there were some missing information. This commit add not yet documented mount options and ioctls. Also it adds sysfs documentation from Documentation/ABI/testing/sysfs-fs-ext4 which was really well hidden, as you can see. Some typo fixes in sysfs-fs-ext4 as well. Signed-off-by: Lukas Czerner <lczerner@...hat.com> --- Documentation/ABI/testing/sysfs-fs-ext4 | 13 ++- Documentation/filesystems/ext4.txt | 209 ++++++++++++++++++++++++++++++- 2 files changed, 218 insertions(+), 4 deletions(-) diff --git a/Documentation/ABI/testing/sysfs-fs-ext4 b/Documentation/ABI/testing/sysfs-fs-ext4 index 5fb7099..f22ac08 100644 --- a/Documentation/ABI/testing/sysfs-fs-ext4 +++ b/Documentation/ABI/testing/sysfs-fs-ext4 @@ -48,7 +48,7 @@ Description: will have its blocks allocated out of its own unique preallocation pool. -What: /sys/fs/ext4/<disk>/inode_readahead +What: /sys/fs/ext4/<disk>/inode_readahead_blks Date: March 2008 Contact: "Theodore Ts'o" <tytso@....edu> Description: @@ -85,7 +85,14 @@ Date: June 2008 Contact: "Theodore Ts'o" <tytso@....edu> Description: Tuning parameter which (if non-zero) controls the goal - inode used by the inode allocator in p0reference to - all other allocation hueristics. This is intended for + inode used by the inode allocator in preference to + all other allocation heuristics. This is intended for debugging use only, and should be 0 on production systems. + +What: /sys/fs/ext4/<disk>/max_writeback_mb_bump +Date: September 2009 +Contact: "Theodore Ts'o" <tytso@....edu> +Description: + The maximum number of megabytes the writeback code will + try to write out before move on to another inode. diff --git a/Documentation/filesystems/ext4.txt b/Documentation/filesystems/ext4.txt index 6ab9442..cd980f7 100644 --- a/Documentation/filesystems/ext4.txt +++ b/Documentation/filesystems/ext4.txt @@ -367,12 +367,47 @@ init_itable=n The lazy itable init code will wait n times the minimizes the impact on the systme performance while file system's inode table is being initialized. -discard Controls whether ext4 should issue discard/TRIM +discard Controls whether ext4 should issue discard/TRIM nodiscard(*) commands to the underlying block device when blocks are freed. This is useful for SSD devices and sparse/thinly-provisioned LUNs, but it is off by default until sufficient testing has been done. +nouid32 Disables 32-bit UIDs and GIDs. This is for + interoperability with older kernels which only + store and expect 16-bit values. + +resize Allows to resize filesystem to the end of the last + existing block group, further resize has to be done + with resize2fs either online, or offline. It can be + used only with conjunction with remount. + +block_validity This options allows to enables/disables the in-kernel +noblock_validity facility for tracking filesystem metadata blocks + within internal data structures. This allows multi- + block allocator and other routines to quickly locate + extents which might overlap with filesystem metadata + blocks. This option is intended for debugging + purposes and since it negatively affects the + performance, it is off by default. + +dioread_lock Controls whether or not ext4 should use the DIO read +dioread_nolock locking. If the dioread_nolock option is specified + ext4 will allocate uninitialized extent before buffer + write and convert the extent to initialized after IO + completes. This approach allows ext4 code to avoid + using inode mutex, which improves scalability on high + speed storages. However this does not work with nobh + option and the mount will fail. Nor does it work with + data journaling and dioread_nolock option will be + ignored with kernel warning. Note that dioread_nolock + code path is only used for extent-based files. + Because of the restrictions this options comprises + it is off by default (e.g. dioread_lock). + +i_version Enable 64-bit inode version support. This option is + off by default. + Data Mode ========= There are 3 different data modes: @@ -400,6 +435,178 @@ needs to be read from and written to disk at the same time where it outperforms all others modes. Currently ext4 does not have delayed allocation support if this data journalling mode is selected. +/proc entries +============= + +Information about mounted ext4 file systems can be found in +/proc/fs/ext4. Each mounted filesystem will have a directory in +/proc/fs/ext4 based on its device name (i.e., /proc/fs/ext4/hdc or +/proc/fs/ext4/dm-0). The files in each per-device directory are shown +in table below. + +Files in /proc/fs/ext4/<devname> +.............................................................................. + File Content + mb_groups details of multiblock allocator buddy cache of free blocks +.............................................................................. + +/sys entries +============ + +Information about mounted ext4 file systems can be found in +/sys/fs/ext4. Each mounted filesystem will have a directory in +/sys/fs/ext4 based on its device name (i.e., /sys/fs/ext4/hdc or +/sys/fs/ext4/dm-0). The files in each per-device directory are shown +in table below. + +Files in /sys/fs/ext4/<devname> +(see also Documentation/ABI/testing/sysfs-fs-ext4) +.............................................................................. + File Content + + delayed_allocation_blocks This file is read-only and shows the number of + blocks that are dirty in the page cache, but + which do not have their location in the + filesystem allocated yet. + + inode_goal Tuning parameter which (if non-zero) controls + the goal inode used by the inode allocator in + preference to all other allocation heuristics. + This is intended for debugging use only, and + should be 0 on production systems. + + inode_readahead_blks Tuning parameter which controls the maximum + number of inode table blocks that ext4's inode + table readahead algorithm will pre-read into + the buffer cache + + lifetime_write_kbytes This file is read-only and shows the number of + kilobytes of data that have been written to this + filesystem since it was created. + + max_writeback_mb_bump The maximum number of megabytes the writeback + code will try to write out before move on to + another inode. + + mb_group_prealloc The multiblock allocator will round up allocation + requests to a multiple of this tuning parameter if + the stripe size is not set in the ext4 superblock + + mb_max_to_scan The maximum number of extents the multiblock + allocator will search to find the best extent + + mb_min_to_scan The minimum number of extents the multiblock + allocator will search to find the best extent + + mb_order2_req Tuning parameter which controls the minimum size + for requests (as a power of 2) where the buddy + cache is used + + mb_stats Controls whether the multiblock allocator should + collect statistics, which are shown during the + unmount. 1 means to collect statistics, 0 means + not to collect statistics + + mb_stream_req Files which have fewer blocks than this tunable + parameter will have their blocks allocated out + of a block group specific preallocation pool, so + that small files are packed closely together. + Each large file will have its blocks allocated + out of its own unique preallocation pool. + + session_write_kbytes This file is read-only and shows the number of + kilobytes of data that have been written to this + filesystem since it was mounted. +.............................................................................. + +Ioctls +====== + +There is some Ext4 specific functionality which can be accessed by applications +through the system call interfaces. The list of all Ext4 specific ioctls are +shown in the table below. + +Table of Ext4 specific ioctls +.............................................................................. + Ioctl Description + EXT4_IOC_GETFLAGS Get additional attributes associated with files + in Ext4. The argument point to the integer. + Meaning of the particular bits are defined in + fs/ext4/ext4. + + EXT4_IOC_SETFLAGS Set additional attributes associated with files + in Ext4. The argument point to the integer. + Meaning of the particular bits are defined in + fs/ext4/ext4. If the file is a subject to quota, + setting inode flags is prohibited. + + EXT4_IOC_GETVERSION + EXT4_IOC_GETVERSION_OLD + Get the inode i_generation number stored for + each inode. This is particularly useful for + NFS in cases when one inode is unlinked and + then a new inode is created with the same inode + number. NFS daemon should know that it is not + the same inode, thus i_generation is needed. + All that said, it is normally changed only when + new inode is created. + + EXT4_IOC_SETVERSION + EXT4_IOC_SETVERSION_OLD + Set the inode i_generation number stored for + each inode. + + EXT4_IOC_GROUP_EXTEND This ioctl has the same purpose as the resize + mount option. It allows to resize filesystem + to the end of the last existing block group, + further resize has to be done with resize2fs, + either online, or offline. The argument points + to the unsigned logn number representing the + filesystem new block count. + + EXT4_IOC_MOVE_EXT Move the block extents from orig_fd (the one + this ioctl is pointing to) to the donor_fd (the + one specified in move_extent structure passed + as an argument to this ioctl). Then, exchange + inode metadata between orig_fd and donor_fd. + This is especially useful for online + defragmentation, because the allocator has the + opportunity to allocate moved blocks better, + ideally into one contiguous extent. + + EXT4_IOC_GROUP_ADD Add a new group descriptor to an existing or + new group descriptor block. The new group + descriptor is described by ext4_new_group_input + structure, which is passed as an argument to + this ioctl. This is especially useful in + conjunction with EXT4_IOC_GROUP_EXTEND, + which allows online resize of the filesystem + to the end of the last existing block group. + Those two ioctls combined is used in userspace + online resize tool (e.g. resize2fs). + + EXT4_IOC_MIGRATE This ioctl operates on the filesystem itself. + It converts (migrates) ext3 indirect block mapped + inode to ext4 extent mapped inode by walking + through indirect block mapping of the original + inode and converting contiguous block ranges + into ext4 extents of the temporary inode. Then, + inodes are swapped. This ioctl might help, when + migrating from ext3 to ext4 filesystem, however + suggestion is to create fresh ext4 filesystem + and copy data from the backup. Note, that + filesystem has to support extents for this ioctl + to work. + + EXT4_IOC_ALLOC_DA_BLKS Force all of the delay allocated blocks to be + allocated to preserve application-expected ext3 + behaviour. Note that this will also start + triggering a write of the data blocks, but this + behaviour may change in the future as it is + not necessary and has been done this way only + for sake of simplicity. +.............................................................................. + References ========== -- 1.7.2.3 -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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