| Message ID | 20250320160541.1635550-1-hch@lst.de (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | design: document the zoned on-disk format | expand |
On Thu, Mar 20, 2025 at 05:05:41PM +0100, Christoph Hellwig wrote: > Document the feature flags, superblock fields and new dinode union. > > Signed-off-by: Christoph Hellwig <hch@lst.de> > --- > .../ondisk_inode.asciidoc | 13 ++++++- > .../realtime.asciidoc | 34 +++++++++++++++++++ > .../superblock.asciidoc | 25 ++++++++++++++ > 3 files changed, 71 insertions(+), 1 deletion(-) > > diff --git a/design/XFS_Filesystem_Structure/ondisk_inode.asciidoc b/design/XFS_Filesystem_Structure/ondisk_inode.asciidoc > index ab4a503b4da6..ba111ebe6e3a 100644 > --- a/design/XFS_Filesystem_Structure/ondisk_inode.asciidoc > +++ b/design/XFS_Filesystem_Structure/ondisk_inode.asciidoc > @@ -139,7 +139,10 @@ struct xfs_dinode_core { > __be64 di_changecount; > __be64 di_lsn; > __be64 di_flags2; > - __be32 di_cowextsize; > + union { > + __be32 di_cowextsize; > + __be32 di_used_blocks; > + }; > __u8 di_pad2[12]; > xfs_timestamp_t di_crtime; > __be64 di_ino; > @@ -425,6 +428,14 @@ the source file to the destination file if the sharing operation completely > overwrites the destination file's contents and the destination file does not > already have +di_cowextsize+ set. > > +*di_used_blocks*:: > + > +Used only for the xref:Real_time_Reverse_Mapping_Btree[Reverse-Mapping B+tree] > +inode on filesystems with a xref:Zoned[Zoned Real-time Device]. Tracks the > +number of filesystem blocks in the rtgroup that have been written but not > +unmapped, i.e. the number of blocks that are referenced by at least one rmap > +entry. > + > *di_pad2*:: > Padding for future expansion of the inode. > > diff --git a/design/XFS_Filesystem_Structure/realtime.asciidoc b/design/XFS_Filesystem_Structure/realtime.asciidoc > index 16641525e201..fff0f691594a 100644 > --- a/design/XFS_Filesystem_Structure/realtime.asciidoc > +++ b/design/XFS_Filesystem_Structure/realtime.asciidoc > @@ -397,3 +397,37 @@ meta_uuid = 7e55b909-8728-4d69-a1fa-891427314eea > include::rtrmapbt.asciidoc[] > > include::rtrefcountbt.asciidoc[] > + > +[[Zoned]] > +== Zoned Real-time Devices > + > +If the +XFS_SB_FEAT_INCOMPAT_ZONED+ feature is enabled, the real time device > +uses an entirely different space allocator. This features does not use the > +xref:Real-Time_Bitmap_Inode[Free Space Bitmap Inode] and > +xref:Real-Time_Summary_Inode[Free Space Summary Inode]. > +Instead, writes to the storage hardware must always occur sequentially > +from the start to the end of a rtgroup. To support this requirement, > +file data are always written out of place using the so called copy on write > +or COW write path (which actually just redirects on write and never copies). > + > +When an rtgroup runs out of space to write, free space is reclaimed by > +copying and remapping still valid data from the full rtgroups into > +another rtgroup. Once the rtgroup is empty, it is written to from the > +beginning again. For this, the > +xref:Real_time_Reverse_Mapping_Btree[Reverse-Mapping B+tree] is required. > + > +For storage hardware that supports hardware zones, each rtgroup is mapped > +to exactly one zone. When a file system is created on a a zoned storage > +device that does support conventional (aka random writable) zones at the > +beginning of the LBA space, those zones are used for the xfs data device > +(which in this case is primarily used for metadata), and the zoned requiring > +sequential writes are presented as the real-time device. But when an external Dumb nit: sentence doesn't need to begin with "But", e.g. "When an external real-time device is used..." Otherwise I think this description matches what I saw in the kernel changes so with that one silly nit fixed, Reviewed-by: "Darrick J. Wong" <djwong@kernel.org> Actually, wait, I'm the maintainer of xfs-docs. I'll fix it on commit if there isn't a v2 in the next week or so. --D > +real-time device is used, rtgroups might also map to conventional zones. > + > +Filesystems with a zoned real-time device by default use the real-time device > +for all data, and the data device only for metadata, which makes the > +terminology a bit confusing. But this is merely the default setting. Like > +any other filesystem with a realtime volume, the +XFS_DIFLAG_REALTIME+ flag > +can be cleared on an empty regular file to target the data device; and the > ++XFS_DIFLAG_RTINHERIT+ flag can be cleared on a directory so that new > +children will target the data device." > diff --git a/design/XFS_Filesystem_Structure/superblock.asciidoc b/design/XFS_Filesystem_Structure/superblock.asciidoc > index f04553046357..bd34eb0d3066 100644 > --- a/design/XFS_Filesystem_Structure/superblock.asciidoc > +++ b/design/XFS_Filesystem_Structure/superblock.asciidoc > @@ -74,6 +74,8 @@ struct xfs_dsb { > __be32 sb_rgextents; > __u8 sb_rgblklog; > __u8 sb_pad[7]; > + __be64 sb_rtstart; > + __be64 sb_rtreserved; > > /* must be padded to 64 bit alignment */ > }; > @@ -449,6 +451,16 @@ pointers] for more information. > Metadata directory tree. See the section about the xref:Metadata_Directories[ > metadata directory tree] for more information. > > +| +XFS_SB_FEAT_INCOMPAT_ZONED+ | > +Zoned RT device. See the section about the xref:Zoned[Zoned Real-time Devices] > +for more information. > + > +| +XFS_SB_FEAT_INCOMPAT_ZONE_GAPS+ | > +Each hardware zone has unusable space at the end of its LBA range, which is > +mirrored by unusable filesystem blocks at the end of the rtgroup. The > ++xfs_rtblock_t startblock+ in file mappings is linearly mapped to the > +hardware LBA space. > + > |===== > > *sb_features_log_incompat*:: > @@ -505,6 +517,19 @@ generate absolute block numbers defined in extent maps from the segmented > *sb_pad[7]*:: > Zeroes, if the +XFS_SB_FEAT_RO_INCOMPAT_METADIR+ feature is enabled. > > +*sb_rtstart*:: > + > +If the +XFS_SB_FEAT_INCOMPAT_ZONED+ feature is enabled, this is the start > +of the internal RT section. That is the RT section is placed on the same > +device as the data device, and starts at this offset into the device. > +The value is in units of file system blocks. > + > +*sb_rtreserved*:: > + > +If the +XFS_SB_FEAT_INCOMPAT_ZONED+ feature is enabled, this is the amount > +of space in the realtime section that is reserved for internal use > +by garbage collection and reorganization algorithms. > + > === xfs_db Superblock Example > > A filesystem is made on a single disk with the following command: > -- > 2.45.2 > >
diff --git a/design/XFS_Filesystem_Structure/ondisk_inode.asciidoc b/design/XFS_Filesystem_Structure/ondisk_inode.asciidoc index ab4a503b4da6..ba111ebe6e3a 100644 --- a/design/XFS_Filesystem_Structure/ondisk_inode.asciidoc +++ b/design/XFS_Filesystem_Structure/ondisk_inode.asciidoc @@ -139,7 +139,10 @@ struct xfs_dinode_core { __be64 di_changecount; __be64 di_lsn; __be64 di_flags2; - __be32 di_cowextsize; + union { + __be32 di_cowextsize; + __be32 di_used_blocks; + }; __u8 di_pad2[12]; xfs_timestamp_t di_crtime; __be64 di_ino; @@ -425,6 +428,14 @@ the source file to the destination file if the sharing operation completely overwrites the destination file's contents and the destination file does not already have +di_cowextsize+ set. +*di_used_blocks*:: + +Used only for the xref:Real_time_Reverse_Mapping_Btree[Reverse-Mapping B+tree] +inode on filesystems with a xref:Zoned[Zoned Real-time Device]. Tracks the +number of filesystem blocks in the rtgroup that have been written but not +unmapped, i.e. the number of blocks that are referenced by at least one rmap +entry. + *di_pad2*:: Padding for future expansion of the inode. diff --git a/design/XFS_Filesystem_Structure/realtime.asciidoc b/design/XFS_Filesystem_Structure/realtime.asciidoc index 16641525e201..fff0f691594a 100644 --- a/design/XFS_Filesystem_Structure/realtime.asciidoc +++ b/design/XFS_Filesystem_Structure/realtime.asciidoc @@ -397,3 +397,37 @@ meta_uuid = 7e55b909-8728-4d69-a1fa-891427314eea include::rtrmapbt.asciidoc[] include::rtrefcountbt.asciidoc[] + +[[Zoned]] +== Zoned Real-time Devices + +If the +XFS_SB_FEAT_INCOMPAT_ZONED+ feature is enabled, the real time device +uses an entirely different space allocator. This features does not use the +xref:Real-Time_Bitmap_Inode[Free Space Bitmap Inode] and +xref:Real-Time_Summary_Inode[Free Space Summary Inode]. +Instead, writes to the storage hardware must always occur sequentially +from the start to the end of a rtgroup. To support this requirement, +file data are always written out of place using the so called copy on write +or COW write path (which actually just redirects on write and never copies). + +When an rtgroup runs out of space to write, free space is reclaimed by +copying and remapping still valid data from the full rtgroups into +another rtgroup. Once the rtgroup is empty, it is written to from the +beginning again. For this, the +xref:Real_time_Reverse_Mapping_Btree[Reverse-Mapping B+tree] is required. + +For storage hardware that supports hardware zones, each rtgroup is mapped +to exactly one zone. When a file system is created on a a zoned storage +device that does support conventional (aka random writable) zones at the +beginning of the LBA space, those zones are used for the xfs data device +(which in this case is primarily used for metadata), and the zoned requiring +sequential writes are presented as the real-time device. But when an external +real-time device is used, rtgroups might also map to conventional zones. + +Filesystems with a zoned real-time device by default use the real-time device +for all data, and the data device only for metadata, which makes the +terminology a bit confusing. But this is merely the default setting. Like +any other filesystem with a realtime volume, the +XFS_DIFLAG_REALTIME+ flag +can be cleared on an empty regular file to target the data device; and the ++XFS_DIFLAG_RTINHERIT+ flag can be cleared on a directory so that new +children will target the data device." diff --git a/design/XFS_Filesystem_Structure/superblock.asciidoc b/design/XFS_Filesystem_Structure/superblock.asciidoc index f04553046357..bd34eb0d3066 100644 --- a/design/XFS_Filesystem_Structure/superblock.asciidoc +++ b/design/XFS_Filesystem_Structure/superblock.asciidoc @@ -74,6 +74,8 @@ struct xfs_dsb { __be32 sb_rgextents; __u8 sb_rgblklog; __u8 sb_pad[7]; + __be64 sb_rtstart; + __be64 sb_rtreserved; /* must be padded to 64 bit alignment */ }; @@ -449,6 +451,16 @@ pointers] for more information. Metadata directory tree. See the section about the xref:Metadata_Directories[ metadata directory tree] for more information. +| +XFS_SB_FEAT_INCOMPAT_ZONED+ | +Zoned RT device. See the section about the xref:Zoned[Zoned Real-time Devices] +for more information. + +| +XFS_SB_FEAT_INCOMPAT_ZONE_GAPS+ | +Each hardware zone has unusable space at the end of its LBA range, which is +mirrored by unusable filesystem blocks at the end of the rtgroup. The ++xfs_rtblock_t startblock+ in file mappings is linearly mapped to the +hardware LBA space. + |===== *sb_features_log_incompat*:: @@ -505,6 +517,19 @@ generate absolute block numbers defined in extent maps from the segmented *sb_pad[7]*:: Zeroes, if the +XFS_SB_FEAT_RO_INCOMPAT_METADIR+ feature is enabled. +*sb_rtstart*:: + +If the +XFS_SB_FEAT_INCOMPAT_ZONED+ feature is enabled, this is the start +of the internal RT section. That is the RT section is placed on the same +device as the data device, and starts at this offset into the device. +The value is in units of file system blocks. + +*sb_rtreserved*:: + +If the +XFS_SB_FEAT_INCOMPAT_ZONED+ feature is enabled, this is the amount +of space in the realtime section that is reserved for internal use +by garbage collection and reorganization algorithms. + === xfs_db Superblock Example A filesystem is made on a single disk with the following command:
Document the feature flags, superblock fields and new dinode union. Signed-off-by: Christoph Hellwig <hch@lst.de> --- .../ondisk_inode.asciidoc | 13 ++++++- .../realtime.asciidoc | 34 +++++++++++++++++++ .../superblock.asciidoc | 25 ++++++++++++++ 3 files changed, 71 insertions(+), 1 deletion(-)