* spl-04-fix-taskq-spinlock-lockup.patch
Fixes a deadlock in the BIO completion handler, due to the taskq code
prematurely re-enabling interrupts when another spinlock had disabled
them in the IDE IRQ handler.
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from Ricardo which removes a dependency on the GPL-only symbol
set_cpus_allowed(). Using this symbol is simpler but in the name
of portability we are adopting a spinlock based solution here
to remove this dependency.
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were added to cover the 3 possible APIs from 2.6.9 to
2.6.26. We attempt to use the newest interfaces and if
not available fallback to the oldest. This a rework of
some changes proposed by Ricardo for RHEL4.
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at a time as I audit it. This chunk finishes moving the SPL entirely
off the linux slab on to the SPL implementation. It differs slightly
from the proposed version in that the spl continues to export to
all the Solaris types and functions. These do conflict with the
Linux slab so a module usings these interfaces must not include the
SPL slab if they also intend to use the linux slab. Or they must
explcitly #undef the macros which remap the functioin to their
spl_* equivilants.
A nice side of effect of dropping the entire linux slab is we
don't need to autoconf checks anymore. They kept messing with
the slab API endlessly!
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based of the spl_kmem_obj_t tacked on the end of each object.
This actually isn't so back because we are now allocing large
chunks for the slab and partitioning it ourselves. So there's
not a ton of wasted space. We may suffer a performance hit
however due to alignment issues.
- Remove remaining depenancies on the linux slab implementation.
We're standing on our own now for better or worse.
- Rework slabs to be either kmem or vmem based. If neither
KMC_VMEM of KMC_KMEM are specified we make a decent guess
about what will work best for their based on the object
size. Additionally we provide a kmem_virt() function caller
can use to see if they have a virtual or physical address.
- Minor fixups in the test suite.
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cycle count which was costing me overhead. It was hurting
performance pretty badly for heavily used caches. I'm also
thinking the hash may be hurting me as well and it might
be worth sticking a pointer in to a little space after the
alloced object.
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based by vmalloc()'ed memory. I now alloc a slab which is
roughly 32*spl_obj_size and in this block of memory I place
the slab descriptor, slab object descriptors, and objects
themselves. This greatly reduces vmalloc lock contention.
Still some minor cleanup remains and fine tuning but
it's working pretty well.
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well for the expected workloads. Improvement in this commit include:
- Added DEBUG_KMEM_TRACKING #define which can optionally be set
when DEBUG_KMEM is defined to do per allocation tracking. This
allows us to get all the lightweight kmem debugging enabled by
default which is pretty light weight, and only when looking
for a memory leak we can briefly enable the per alloc tracking.
- Added set_normalized_timespec() in to SPL to simply using
the timespec() primatives from within a module.
- Added per-spinlock cycle counters to the slab in an attempt
to run down a lock contention issue. The contended lock
was in vmalloc() but I'm going to leave the cycle counters
in place for a little while until I'm convinced there arn't
other locking improvement possible in the slab.
- Added a proc interface to the slab to export per slab
cache statistics to /proc/spl/kmem/slab for analysis.
- Reworked spl_slab_alloc() function to allocate from kmem for
small allocation and vmem for large allocations. This improved
things considerably but futher work is needed.
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when repopulating it. Plus I fixed a few more suble races in
that part of the code which were catching me. Finally I fixed
a small race in kmem_test8.
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factor of 10x improvement on SMP system due to reduced lock contention.
This may put me in the ballpark of what is needed. We can still further
improve things on NUMA systems by creating an additional L3 cache per
memory node instead of the current global pool. With luck this won't
be needed. I should also take another look at the locking now that
everything is working. There's a good chance I can tighten it up a
little bit and improve things a little more.
kmem_lock: time (sec) slabs objs hash
kmem_lock: tot/max/calc tot/max/calc size/depth
kmem_lock: 0.000999926 6/6/1 192/192/32 32768/0
kmem_lock: 0.000999926 4/4/2 128/128/64 32768/0
kmem_lock: 0.000999926 4/4/4 128/128/128 32768/0
kmem_lock: 0.000999926 4/4/8 128/128/256 32768/0
kmem_lock: 0.000999926 4/4/16 128/128/512 32768/0
kmem_lock: 0.000999926 4/4/32 128/128/1024 32768/0
kmem_lock: 0.000999926 4/4/64 128/128/2048 32768/0
kmem_lock: 0.000999926 8/8/128 256/256/4096 32768/0
kmem_lock: 0.003999704 24/23/256 768/736/8192 32768/1
kmem_lock: 0.012999038 44/41/512 1408/1312/16384 32768/1
kmem_lock: 0.051996153 96/93/1024 3072/2976/32768 32768/2
kmem_lock: 0.181986536 187/184/2048 5984/5888/65536 32768/3
kmem_lock: 0.655951469 342/339/4096 10944/10848/131072 32768/4
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to be overly clever and the context switch when the semaphore was busy
was destroying performance. Converting to a simple spin lock bough me
a factor of 50 or so. That said it's still not good enough. Tests
show bad performance and we are still CPU bound. The logical fix is
I need to implement per-cpu hot caches to minimize the SMP contention.
Linux and Solaris both have this, I was hoping to do without but it
looks like that's not to be.
kmem_lock: time (sec) slabs objs hash
kmem_lock: tot/max/calc tot/max/calc size/depth
kmem_lock: 0.022000000 7/6/64 224/177/2048 32768/1
kmem_lock: 0.039000000 13/13/128 416/404/4096 32768/1
kmem_lock: 0.079000000 23/21/256 736/672/8192 32768/1
kmem_lock: 0.158000000 48/47/512 1536/1504/16384 32768/1
kmem_lock: 0.345000000 105/105/1024 3360/3358/32768 32768/2
kmem_lock: 0.760000000 202/200/2048 6464/6400/65536 32768/3
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longer be based on the linux slab but to be its own complete
implementation. The new slab behaves much more like the
Solaris slab than the Linux slab.
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1) Ensure mutex_init() never fails in the case of ENOMEM by retrying
forever. I don't think I've ever seen this happen but it was clear
after code inspection that if it did we would immediately crash.
2) Enable full debugging in check.sh for sanity tests. Might as well
get as much debug as we can in the case of a failure.
3) Reworked list of kmem caches tracked by SPL in to a hash with the
key based on the address of the kmem_cache_t. This should speed
up the constructor/destructor/shrinker lookup needed now for newer
kernel which removed the destructor support.
4) Updated kmem_cache_create to handle the case where CONFIG_SLUB
is defined. The slub would occasionally merge slab caches which
resulted in non-unique keys for our hash lookup in 3). To fix this
we detect if the slub is enabled and then set the needed flag
to prevent this merging from ever occuring.
5) New kernels removed the proc_dir_entry pointer from items
registered by sysctl. This means we can no long be sneaky and
manually insert things in to the sysctl tree simply by walking
the proc tree. So I'm forced to create a seperate tree for
all the things I can't easily support via sysctl interface.
I don't like it but it will do for now.
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working on this branch for the next few days I suggested you work
off of the 0.3.1 tag. The following changes are fairly extensive
and are designed to make the SPL compatible with all kernels in
the range of 2.6.18-2.6.25. There were 13 relevant API changes
between these releases and I have added the needed autoconf tests
to check for them. However, this has not all been tested extensively.
I'll sort of the breakage on Fedora Core 9 and RHEL5 this week.
SPL_AC_TYPE_UINTPTR_T
SPL_AC_TYPE_KMEM_CACHE_T
SPL_AC_KMEM_CACHE_DESTROY_INT
SPL_AC_ATOMIC_PANIC_NOTIFIER
SPL_AC_3ARGS_INIT_WORK
SPL_AC_2ARGS_REGISTER_SYSCTL
SPL_AC_KMEM_CACHE_T
SPL_AC_KMEM_CACHE_CREATE_DTOR
SPL_AC_3ARG_KMEM_CACHE_CREATE_CTOR
SPL_AC_SET_SHRINKER
SPL_AC_PATH_IN_NAMEIDATA
SPL_AC_TASK_CURR
SPL_AC_CTL_UNNUMBERED
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compiled out when doing performance runs.
- Bite the bullet and fully autoconfize the debug options in the configure
time parameters. By default all the debug support is disable in the core
SPL build, but available to modules which enable it when building against
the SPL. To enable particular SPL debug support use the follow configure
options:
--enable-debug Internal ASSERTs
--enable-debug-kmem Detailed memory accounting
--enable-debug-mutex Detailed mutex tracking
--enable-debug_kstat Kstat info exported to /proc
--enable-debug-callb Additional callb debug
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other primitive implementations. Additionally ensure that GFP_ATOMIC
is use for allocations when in interrupt context.
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may not fail. To get this behavior I'd added a retry to the shim layer
even though it is abusive to the VM, at least it should prevent the crash.
Additionally I added a proc counter so I can easily check how often this
is happening. It should be fairly rare, but likely will get worse and
worse the longer the machine has been up.
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not to support a few flags (we assert if they are used), and I
did not add the libkstat interface and instead exported everything
to proc for easy access.
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- Ensure the mutex_stats_sem and mutex_stats_list are initialized
- Only spin if you have to in mutex_init
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- Detailed kmem memory allocation tracking. We can now get on
spl module unload a list of all memory allocations which were
not free'd and where the original alloc was. E.g.
SPL: 15554:632:(spl-kmem.c:442:kmem_fini()) kmem leaked 90/319332 bytes
SPL: 15554:648:(spl-kmem.c:451:kmem_fini()) address size data func:line
SPL: 15554:648:(spl-kmem.c:457:kmem_fini()) ffff8100734b68b8 32 0100000001005a5a __spl_mutex_init:70
SPL: 15554:648:(spl-kmem.c:457:kmem_fini()) ffff8100734b6148 13 &tl->tl_lock __spl_mutex_init:74
SPL: 15554:648:(spl-kmem.c:457:kmem_fini()) ffff81007ac43730 32 0100000001005a5a __spl_mutex_init:70
SPL: 15554:648:(spl-kmem.c:457:kmem_fini()) ffff81007ac437d8 13 &tl->tl_lock __spl_mutex_init:74
- Shift to using rwsems in kmem implmentation, to simply locking and
improve concurency.
- Shift to using rwsems in mutex implementation, additionally ensure we
never sleep in the init function if non-zero preempt_count or
interrupts are disabled as can happen in a slab cache ctor/dtor.
- Other minor formating fixes and such.
TODO:
- Finish the vmem memory allocation tracking
- Vet all other SPL primatives for potential sleeping during *_init. I
suspect the rwlock implemenation does this and should be fixes just
like the mutex implemenation.
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crashes but it's not clear to me yet if these are a problem with
the mutex implementation or ZFSs usage of it.
Minor taskq fixes to add new tasks to the end of the pending list.
Minor enhansements to the debug infrastructure.
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configurable number of threads like the Solaris version and almost
all of the options are supported. Unfortunately, it appears to have
made absolutely no difference to our performance numbers. I need
to keep looking for where we are bottle necking.
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do not have __GFP_ZERO set. Once the memory is allocated
then zero out the memory if __GFP_ZERO is passed to
__vmem_alloc.
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ensure I never add anything to the stack I don't absolutely need.
All this debug code could be removed from a production build
anyway so I'm not so worried about the performance impact. We
may also consider revisting the mutex and condvar implementation
to ensure no additional stack is used there.
Initial indications are I have reduced the worst case stack
usage to 9080 bytes. Still to large for the default 8k stacks
so I have been forced to run with 16k stacks until I can
reduce the worst offenders.
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process of destroying the stacks. Threshhold set fairly aggressively
top 80% of stack usage.
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- Replacing all BUG_ON()'s with proper ASSERT()'s
- Using ENTRY,EXIT,GOTO, and RETURN macro to instument call paths
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changes bring over everything lustre had for debugging with
two exceptions. I dropped by the debug daemon and upcalls
just because it made things a little easier. They can be
readded easily enough if we feel they are needed.
Everything compiles and seems to work on first inspection
but I suspect there are a handful of issues still lingering
which I'll be sorting out right away. I just wanted to get
all these changes commited and safe. I'm getting a little
paranoid about losing them.
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think this should fix anything but it's a good idea regardless.
- Drop the lock before calling the construct/destructor for the slab
otherwise we can't sleep in a constructor/destructor and for long running
functions we may NMI.
- Do something braindead, but safe for the console debug logs for now.
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