From: Darrick J. Wong <djwong@xxxxxxxxxx> In preparation for documenting the realtime modernization project, move the discussions of the realtime-realted ondisk metadata to a separate file. Since realtime reverse mapping btrees haven't been added to the filesystem yet, stop including them in the final output. Signed-off-by: Darrick J. Wong <djwong@xxxxxxxxxx> Reviewed-by: Christoph Hellwig <hch@xxxxxx> --- .../allocation_groups.asciidoc | 20 -------- .../internal_inodes.asciidoc | 36 +------------- design/XFS_Filesystem_Structure/realtime.asciidoc | 50 ++++++++++++++++++++ .../xfs_filesystem_structure.asciidoc | 2 + 4 files changed, 54 insertions(+), 54 deletions(-) create mode 100644 design/XFS_Filesystem_Structure/realtime.asciidoc diff --git a/design/XFS_Filesystem_Structure/allocation_groups.asciidoc b/design/XFS_Filesystem_Structure/allocation_groups.asciidoc index e2cdaab5e03d3f..c746a92ca47dd6 100644 --- a/design/XFS_Filesystem_Structure/allocation_groups.asciidoc +++ b/design/XFS_Filesystem_Structure/allocation_groups.asciidoc @@ -772,23 +772,3 @@ core.magic = 0x494e The chunk record also indicates that this chunk has 32 inodes, and that the missing inodes are also ``free''. - -[[Real-time_Devices]] -== Real-time Devices - -The performance of the standard XFS allocator varies depending on the internal -state of the various metadata indices enabled on the filesystem. For -applications which need to minimize the jitter of allocation latency, XFS -supports the notion of a ``real-time device''. This is a special device -separate from the regular filesystem where extent allocations are tracked with -a bitmap and free space is indexed with a two-dimensional array. If an inode -is flagged with +XFS_DIFLAG_REALTIME+, its data will live on the real time -device. The metadata for real time devices is discussed in the section about -xref:Real-time_Inodes[real time inodes]. - -By placing the real time device (and the journal) on separate high-performance -storage devices, it is possible to reduce most of the unpredictability in I/O -response times that come from metadata operations. - -None of the XFS per-AG B+trees are involved with real time files. It is not -possible for real time files to share data blocks. diff --git a/design/XFS_Filesystem_Structure/internal_inodes.asciidoc b/design/XFS_Filesystem_Structure/internal_inodes.asciidoc index eaa0a50aa848f3..68c86d30ff8206 100644 --- a/design/XFS_Filesystem_Structure/internal_inodes.asciidoc +++ b/design/XFS_Filesystem_Structure/internal_inodes.asciidoc @@ -287,41 +287,9 @@ Log sequence number of the last DQ block write. *dd_crc*:: Checksum of the DQ block. - [[Real-time_Inodes]] == Real-time Inodes There are two inodes allocated to managing the real-time device's space, the -Bitmap Inode and the Summary Inode. - -[[Real-Time_Bitmap_Inode]] -=== Real-Time Bitmap Inode - -The real time bitmap inode, +sb_rbmino+, tracks the used/free space in the -real-time device using an old-style bitmap. One bit is allocated per real-time -extent. The size of an extent is specified by the superblock's +sb_rextsize+ -value. - -The number of blocks used by the bitmap inode is equal to the number of -real-time extents (+sb_rextents+) divided by the block size (+sb_blocksize+) -and bits per byte. This value is stored in +sb_rbmblocks+. The nblocks and -extent array for the inode should match this. Each real time block gets its -own bit in the bitmap. - -[[Real-Time_Summary_Inode]] -=== Real-Time Summary Inode - -The real time summary inode, +sb_rsumino+, tracks the used and free space -accounting information for the real-time device. This file indexes the -approximate location of each free extent on the real-time device first by -log2(extent size) and then by the real-time bitmap block number. The size of -the summary inode file is equal to +sb_rbmblocks+ × log2(realtime device size) -× sizeof(+xfs_suminfo_t+). The entry for a given log2(extent size) and -rtbitmap block number is 0 if there is no free extents of that size at that -rtbitmap location, and positive if there are any. - -This data structure is not particularly space efficient, however it is a very -fast way to provide the same data as the two free space B+trees for regular -files since the space is preallocated and metadata maintenance is minimal. - -include::rtrmapbt.asciidoc[] +xref:Real-Time_Bitmap_Inode[Bitmap Inode] and the +xref:Real-Time_Summary_Inode[Summary Inode]. diff --git a/design/XFS_Filesystem_Structure/realtime.asciidoc b/design/XFS_Filesystem_Structure/realtime.asciidoc new file mode 100644 index 00000000000000..11426e8fdb632d --- /dev/null +++ b/design/XFS_Filesystem_Structure/realtime.asciidoc @@ -0,0 +1,50 @@ +[[Real-time_Devices]] += Real-time Devices + +The performance of the standard XFS allocator varies depending on the internal +state of the various metadata indices enabled on the filesystem. For +applications which need to minimize the jitter of allocation latency, XFS +supports the notion of a ``real-time device''. This is a special device +separate from the regular filesystem where extent allocations are tracked with +a bitmap and free space is indexed with a two-dimensional array. If an inode +is flagged with +XFS_DIFLAG_REALTIME+, its data will live on the real time +device. + +By placing the real time device (and the journal) on separate high-performance +storage devices, it is possible to reduce most of the unpredictability in I/O +response times that come from metadata operations. + +None of the XFS per-AG B+trees are involved with real time files. It is not +possible for real time files to share data blocks. + +[[Real-Time_Bitmap_Inode]] +== Free Space Bitmap Inode + +The real time bitmap inode, +sb_rbmino+, tracks the used/free space in the +real-time device using an old-style bitmap. One bit is allocated per real-time +extent. The size of an extent is specified by the superblock's +sb_rextsize+ +value. + +The number of blocks used by the bitmap inode is equal to the number of +real-time extents (+sb_rextents+) divided by the block size (+sb_blocksize+) +and bits per byte. This value is stored in +sb_rbmblocks+. The nblocks and +extent array for the inode should match this. Each real time block gets its +own bit in the bitmap. + +[[Real-Time_Summary_Inode]] +== Free Space Summary Inode + +The real time summary inode, +sb_rsumino+, tracks the used and free space +accounting information for the real-time device. This file indexes the +approximate location of each free extent on the real-time device first by +log2(extent size) and then by the real-time bitmap block number. The size of +the summary inode file is equal to +sb_rbmblocks+ × log2(realtime device size) +× sizeof(+xfs_suminfo_t+). The entry for a given log2(extent size) and +rtbitmap block number is 0 if there is no free extents of that size at that +rtbitmap location, and positive if there are any. + +This data structure is not particularly space efficient, however it is a very +fast way to provide the same data as the two free space B+trees for regular +files since the space is preallocated and metadata maintenance is minimal. + +include::rtrmapbt.asciidoc[] diff --git a/design/XFS_Filesystem_Structure/xfs_filesystem_structure.asciidoc b/design/XFS_Filesystem_Structure/xfs_filesystem_structure.asciidoc index 689e2a874c13e9..a643d18add6094 100644 --- a/design/XFS_Filesystem_Structure/xfs_filesystem_structure.asciidoc +++ b/design/XFS_Filesystem_Structure/xfs_filesystem_structure.asciidoc @@ -84,6 +84,8 @@ include::journaling_log.asciidoc[] include::internal_inodes.asciidoc[] +include::realtime.asciidoc[] + include::fs_properties.asciidoc[] :leveloffset: 0
