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Merge git://git.kernel.org/pub/scm/linux/kernel/git/steve/gfs2-3.0-nmw
Pull GFS2 changes from Steven Whitehouse. * git://git.kernel.org/pub/scm/linux/kernel/git/steve/gfs2-3.0-nmw: (24 commits) GFS2: Fix quota adjustment return code GFS2: Add rgrp information to block_alloc trace point GFS2: Eliminate unused "new" parameter to gfs2_meta_indirect_buffer GFS2: Update glock doc to add new stats info GFS2: Update main gfs2 doc GFS2: Remove redundant metadata block type check GFS2: Fix sgid propagation when using ACLs GFS2: eliminate log elements and simplify GFS2: Eliminate vestigial sd_log_le_rg GFS2: Eliminate needless parameter from function gfs2_setbit GFS2: Log code fixes GFS2: Remove unused argument from gfs2_internal_read GFS2: Remove bd_list_tr GFS2: Remove duplicate log code GFS2: Clean up log write code path GFS2: Use variable rather than qa to determine if unstuff necessary GFS2: Change variable blk to biblk GFS2: Fix function parameter comments in rgrp.c GFS2: Eliminate offset parameter to gfs2_setbit GFS2: Use slab for block reservation memory ...
This commit is contained in:
Linus Torvalds
commit
62c8d92278
23 changed files with 588 additions and 499 deletions
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@ -61,7 +61,9 @@ go_unlock | Called on the final local unlock of a lock
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go_dump | Called to print content of object for debugfs file, or on
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| error to dump glock to the log.
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go_type | The type of the glock, LM_TYPE_.....
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go_min_hold_time | The minimum hold time
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go_callback | Called if the DLM sends a callback to drop this lock
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go_flags | GLOF_ASPACE is set, if the glock has an address space
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| associated with it
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The minimum hold time for each lock is the time after a remote lock
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grant for which we ignore remote demote requests. This is in order to
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@ -89,6 +91,7 @@ go_demote_ok | Sometimes | Yes
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go_lock | Yes | No
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go_unlock | Yes | No
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go_dump | Sometimes | Yes
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go_callback | Sometimes (N/A) | Yes
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N.B. Operations must not drop either the bit lock or the spinlock
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if its held on entry. go_dump and do_demote_ok must never block.
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@ -111,4 +114,118 @@ itself (locking order as above), and the other, known as the iopen
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glock is used in conjunction with the i_nlink field in the inode to
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determine the lifetime of the inode in question. Locking of inodes
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is on a per-inode basis. Locking of rgrps is on a per rgrp basis.
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In general we prefer to lock local locks prior to cluster locks.
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Glock Statistics
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------------------
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The stats are divided into two sets: those relating to the
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super block and those relating to an individual glock. The
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super block stats are done on a per cpu basis in order to
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try and reduce the overhead of gathering them. They are also
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further divided by glock type. All timings are in nanoseconds.
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In the case of both the super block and glock statistics,
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the same information is gathered in each case. The super
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block timing statistics are used to provide default values for
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the glock timing statistics, so that newly created glocks
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should have, as far as possible, a sensible starting point.
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The per-glock counters are initialised to zero when the
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glock is created. The per-glock statistics are lost when
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the glock is ejected from memory.
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The statistics are divided into three pairs of mean and
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variance, plus two counters. The mean/variance pairs are
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smoothed exponential estimates and the algorithm used is
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one which will be very familiar to those used to calculation
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of round trip times in network code. See "TCP/IP Illustrated,
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Volume 1", W. Richard Stevens, sect 21.3, "Round-Trip Time Measurement",
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p. 299 and onwards. Also, Volume 2, Sect. 25.10, p. 838 and onwards.
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Unlike the TCP/IP Illustrated case, the mean and variance are
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not scaled, but are in units of integer nanoseconds.
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The three pairs of mean/variance measure the following
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things:
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1. DLM lock time (non-blocking requests)
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2. DLM lock time (blocking requests)
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3. Inter-request time (again to the DLM)
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A non-blocking request is one which will complete right
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away, whatever the state of the DLM lock in question. That
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currently means any requests when (a) the current state of
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the lock is exclusive, i.e. a lock demotion (b) the requested
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state is either null or unlocked (again, a demotion) or (c) the
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"try lock" flag is set. A blocking request covers all the other
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lock requests.
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There are two counters. The first is there primarily to show
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how many lock requests have been made, and thus how much data
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has gone into the mean/variance calculations. The other counter
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is counting queuing of holders at the top layer of the glock
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code. Hopefully that number will be a lot larger than the number
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of dlm lock requests issued.
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So why gather these statistics? There are several reasons
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we'd like to get a better idea of these timings:
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1. To be able to better set the glock "min hold time"
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2. To spot performance issues more easily
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3. To improve the algorithm for selecting resource groups for
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allocation (to base it on lock wait time, rather than blindly
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using a "try lock")
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Due to the smoothing action of the updates, a step change in
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some input quantity being sampled will only fully be taken
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into account after 8 samples (or 4 for the variance) and this
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needs to be carefully considered when interpreting the
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results.
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Knowing both the time it takes a lock request to complete and
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the average time between lock requests for a glock means we
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can compute the total percentage of the time for which the
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node is able to use a glock vs. time that the rest of the
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cluster has its share. That will be very useful when setting
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the lock min hold time.
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Great care has been taken to ensure that we
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measure exactly the quantities that we want, as accurately
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as possible. There are always inaccuracies in any
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measuring system, but I hope this is as accurate as we
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can reasonably make it.
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Per sb stats can be found here:
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/sys/kernel/debug/gfs2/<fsname>/sbstats
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Per glock stats can be found here:
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/sys/kernel/debug/gfs2/<fsname>/glstats
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Assuming that debugfs is mounted on /sys/kernel/debug and also
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that <fsname> is replaced with the name of the gfs2 filesystem
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in question.
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The abbreviations used in the output as are follows:
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srtt - Smoothed round trip time for non-blocking dlm requests
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srttvar - Variance estimate for srtt
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srttb - Smoothed round trip time for (potentially) blocking dlm requests
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srttvarb - Variance estimate for srttb
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sirt - Smoothed inter-request time (for dlm requests)
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sirtvar - Variance estimate for sirt
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dlm - Number of dlm requests made (dcnt in glstats file)
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queue - Number of glock requests queued (qcnt in glstats file)
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The sbstats file contains a set of these stats for each glock type (so 8 lines
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for each type) and for each cpu (one column per cpu). The glstats file contains
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a set of these stats for each glock in a similar format to the glocks file, but
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using the format mean/variance for each of the timing stats.
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The gfs2_glock_lock_time tracepoint prints out the current values of the stats
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for the glock in question, along with some addition information on each dlm
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reply that is received:
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status - The status of the dlm request
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flags - The dlm request flags
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tdiff - The time taken by this specific request
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(remaining fields as per above list)
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@ -1,7 +1,7 @@
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Global File System
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------------------
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http://sources.redhat.com/cluster/wiki/
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https://fedorahosted.org/cluster/wiki/HomePage
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GFS is a cluster file system. It allows a cluster of computers to
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simultaneously use a block device that is shared between them (with FC,
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@ -30,7 +30,8 @@ needed, simply:
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If you are using Fedora, you need to install the gfs2-utils package
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and, for lock_dlm, you will also need to install the cman package
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and write a cluster.conf as per the documentation.
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and write a cluster.conf as per the documentation. For F17 and above
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cman has been replaced by the dlm package.
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GFS2 is not on-disk compatible with previous versions of GFS, but it
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is pretty close.
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@ -39,8 +40,6 @@ The following man pages can be found at the URL above:
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fsck.gfs2 to repair a filesystem
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gfs2_grow to expand a filesystem online
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gfs2_jadd to add journals to a filesystem online
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gfs2_tool to manipulate, examine and tune a filesystem
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gfs2_quota to examine and change quota values in a filesystem
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tunegfs2 to manipulate, examine and tune a filesystem
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gfs2_convert to convert a gfs filesystem to gfs2 in-place
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mount.gfs2 to help mount(8) mount a filesystem
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mkfs.gfs2 to make a filesystem
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