This commit preserves the recursive function dbuf_hold_impl() but moves
the local variables and function arguments to the heap to minimize
the stack frame size. Enough space is initially allocated on the
stack for 20 levels of recursion. This technique was based on commit
34229a2f2a which reduced stack usage of
traverse_visitbp().
dbuf_hold_impl() is mutually recursive with dbuf_findbp(),
but the latter function is also called from other functions.
Therefore dbuf_findbp() must contain logic to determine how to call
dbuf_hold_impl(). To this end, dbuf_hold_impl() now takes a
struct dbuf_hold_impl_data pointer as an argument. If that argument
is NULL it calls dbuf_hold_impl() as before, otherwise it calls
__debuf_hold_impl() with a single dbuf_hold_impl_data pointer argument.
As the name implies, dbuf_hold_impl_data stores the arguments and local
variables for dbuf_hold_impl().
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Github issue 22 reported a stack overrun when the zfs module was
loaded, possibly related to the presence of existing zpools created
under zfs-fuse. The stack trace showed 9 levels of recursion between
dsl_scan_visitbp() and dsl_scan_recurse(). To reduce stack overhead in
that code path, this commit moves the 128 byte blkptr_t data strucutre
in dsl_scan_visitbp() to the heap.
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Eliminated local variables pointing to members of the zio struct.
Just refer to the struct members directly. This saved about 32 bytes per
call, but this function can be called recurisvely up to 19 levels deep,
so we potentially save up to 608 bytes.
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Deep recursive call chains are contributing to segfaults in ztest due to
heavy stack use. Inlining zio_execute() helps reduce the stack depth of
the zio_notify_parent() -> zio_execute() -> zio_wait() recursive cycle.
I am no longer seeing ztest segfaults in this code path with this change.
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Deep recursive call chains are contributing to segfaults in ztest due
to heavy stack use. Inlining dbuf_findbp() helps reduce the stack depth
of the dbuf_findbp() -> dbuf_hold_impl() cycle. However, segfaults are
still occurring in this code path, so further reductions are still needed.
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Deep recursive call chains are contributing to segfaults in ztest due
to heavy stack use. Inlining zio_notify_parent() helps reduce the
stack depth of the zio_notify_parent() -> zio_execute() -> zio_done()
recursive cycle. I am no longer seeing ztest segfaults in this code
path with this change combined with the zio_done() stack reduction in
the previous commit.
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
The spa_load function may call itself recursively through
the spa_load_impl function. This call path of spa_load->
spa_load_impl->spa_load->spa_load_impl takes 640 bytes of
stack. By forcing spa_load_impl to be inlined as part of
spa_load the can be reduced to 448 bytes, for a savings of
192 bytes,
A number of ztest functions create one or more 312B ztest_od_t data
structures. To conserve stack usage, this commit moves all of these data
structures to the heap. However, I am still seeing ztest segfaults due
to heavy stack usage of the dbuf_findbp() -> dbuf_hold_impl() recursion.
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
The feature branch 'fix-taskq' in Linux's ZFS tree changes the taskq_dispatch()
flag from TQ_SLEEP to TQ_NOSLEEP to avoid sleeping in some circumstances.
However, this has the side effect that taskq_dispatch() now may fail, and since
the return code was not even being checked, it could lead to zio's not being
scheduled to execute.
I'm fixing this in a simplistic but not very elegant way, by just looping until
taskq_dispatch() succeeds.
Signed-off-by: Ricardo M. Correia <ricardo.correia@oracle.com>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Some buggy NPTL threading implementations include the guard area within
the stack size allocations. In this case we need to allocate an extra
page to account for the guard area since we only have two pages of usable
stack on Linux. Added an autoconf test that detects such implementations
by running a test program designed to segfault if the bug is present.
Set a flag NPTL_GUARD_WITHIN_STACK that is tested to decide if extra
stack space must be allocated for the guard area.
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Brian Behlendorf
Ned Bass
Ricardo M. Correia