c1220522 - xfs: grant heads track byte counts, not LSNs

Thu, 20 Jun 2024 07:21:27 +0000

xfs: grant heads track byte counts, not LSNsThe grant heads in the log track the space reserved in the log forrunning transactions. They do this by tracking how far ahead of thetail that the reservation has reached, and the units for doing thisare {cycle,bytes} for the reserve head rather than {cycle,blocks}which are normal used by LSNs.This is annoyingly complex because we have to split, crack andcombined these tuples for any calculation we do to determine logspace and targets. This is computationally expensive as well asdifficult to do atomically and locklessly, as well as limiting thesize of the log to 2^32 bytes.Really, though, all the grant heads are tracking is how much spaceis currently available for use in the log. We can track this as asimply byte count - we just don't care what the actual physicallocation in the log the head and tail are at, just how much space wehave remaining before the head and tail overlap.So, convert the grant heads to track the byte reservations that areactive rather than the current (cycle, offset) tuples. This means anempty log has zero bytes consumed, and a full log is when thereservations reach the size of the log minus the space consumed bythe AIL.This greatly simplifies the accounting and checks for whether thereis space available. We no longer need to crack or combine LSNs todetermine how much space the log has left, nor do we need to look atthe head or tail of the log to determine how close to full we are.There is, however, a complexity that needs to be handled. We knowhow much space is being tracked in the AIL now via log->l_tail_spaceand the log tickets track active reservations and return the unusedportions to the grant heads when ungranted. Unfortunately, we don'ttrack the used portion of the grant, so when we transfer log itemsfrom the CIL to the AIL, the space accounted to the grant heads istransferred to the log tail space. Hence when we move the AIL headforwards on item insert, we have to remove that space from the grantheads.We also remove the xlog_verify_grant_tail() debug function as it isno longer useful. The check it performs has been racy since delayedlogging was introduced, but now it is clearly only detecting falsepositives so remove it.The result of this substantially simpler accounting algorithm is anincrease in sustained transaction rate from ~1.3 milliontransactions/s to ~1.9 million transactions/s with no increase inCPU usage. We also remove the 32 bit space limitation on the grantheads, which will allow us to increase the journal size beyond 2GBin future.Note that this renames the sysfs files exposing the log grant spacenow that the values are exported in bytes. This allows xfsteststo auto-detect the old or new ABI.[hch: move xlog_grant_sub_space out of line, update the xlog_grant_{add,sub}_space prototypes, rename the sysfs files to allow auto-detection in xfstests]Signed-off-by: Dave Chinner Reviewed-by: Darrick J. Wong Signed-off-by: Christoph Hellwig Reviewed-by: Dave Chinner Signed-off-by: Chandan Babu R List of files: /linux-6.15/Documentation/ABI/testing/sysfs-fs-xfs

9ff4490e - xfs: fix the contact address for the sysfs ABI documentation

Thu, 20 Jun 2024 07:21:18 +0000

xfs: fix the contact address for the sysfs ABI documentationoss.sgi.com is long dead, refer to the current linux-xfs list instead.Signed-off-by: Christoph Hellwig Reviewed-by: Darrick J. Wong Signed-off-by: Chandan Babu R List of files: /linux-6.15/Documentation/ABI/testing/sysfs-fs-xfs

08a20438 - docs: ABI: Fix the spelling oustanding to outstanding in the file sysfs-fs-xfs

Tue, 09 Mar 2021 17:45:51 +0000

docs: ABI: Fix the spelling oustanding to outstanding in the file sysfs-fs-xfss/oustanding/outstanding/Signed-off-by: Bhaskar Chowdhury Reviewed-by: Darrick J. Wong Signed-off-by: Darrick J. Wong List of files: /linux-6.15/Documentation/ABI/testing/sysfs-fs-xfs

a0874818 - xfs: document log sysfs attributes in testing ABI

Mon, 14 Jul 2014 22:09:06 +0000

xfs: document log sysfs attributes in testing ABICreate a sysfs-fs-xfs ABI documentation file for newly added sysfsattributes. This is created under the testing section.Signed-off-by: Brian Foster Reviewed-by: Dave Chinner Signed-off-by: Dave Chinner List of files: /linux-6.15/Documentation/ABI/testing/sysfs-fs-xfs

Changes in sysfs-fs-xfs

c1220522 - xfs: grant heads track byte counts, not LSNs

9ff4490e - xfs: fix the contact address for the sysfs ABI documentation

08a20438 - docs: ABI: Fix the spelling oustanding to outstanding in the file sysfs-fs-xfs

a0874818 - xfs: document log sysfs attributes in testing ABI