Commits on Jun 29, 2012

1. Revert Fix ASSERTION(!dsl_pool_sync_context(tx->tx_pool)) …

   Commit eec8164 worked around an issue
   involving direct reclaim through the use of PF_MEMALLOC.   Since we
   are reworking thing to use KM_PUSHPAGE so that swap works, we revert
   this patch in favor of the use of KM_PUSHPAGE in the affected areas.
   
   Signed-off-by: Richard Yao <ryao@cs.stonybrook.edu>
   Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
   Issue openzfs#726

   

   ryao committed Jun 29, 2012
   Copy the full SHA

   7fdf111 View commit details

   Browse the repository at this point in the history

2. Revert Fix zpl_writepage() deadlock …

   The commit, cfc9a5c, to fix deadlocks
   in zpl_writepage() relied on PF_MEMALLOC.   That had the effect of
   disabling the direct reclaim path on all allocations originating from
   calls to this function, but it failed to address the actual cause of
   those deadlocks.  This led to the same deadlocks being observed with
   swap on zvols, but not with swap on the loop device, which exercises
   this code.
   
   The use of PF_MEMALLOC also had the side effect of permitting
   allocations to be made from ZONE_DMA in instances that did not require
   it.  This contributes to the possibility of panics caused by depletion
   of pages from ZONE_DMA.
   
   As such, we revert this patch in favor of a proper fix for both issues.
   
   Signed-off-by: Richard Yao <ryao@cs.stonybrook.edu>
   Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
   Issue openzfs#726

   

   ryao committed Jun 29, 2012
   Copy the full SHA

   77d8b3e View commit details

   Browse the repository at this point in the history

3. Revert Disable direct reclaim for z_wr_* threads …

   This commit used PF_MEMALLOC to prevent a memory reclaim deadlock.
   However, commit 49be0cc eliminated
   the invocation of __cv_init(), which was the cause of the deadlock.
   PF_MEMALLOC has the side effect of permitting pages from ZONE_DMA
   to be allocated.  The use of PF_MEMALLOC was found to cause stability
   problems when doing swap on zvols. Since this technique is known to
   cause problems and no longer fixes anything, we revert it.
   
   Signed-off-by: Richard Yao <ryao@cs.stonybrook.edu>
   Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
   Issue openzfs#726

   

   ryao committed Jun 29, 2012
   Copy the full SHA

   1dfb3c3 View commit details

   Browse the repository at this point in the history

4. Switch KM_SLEEP to KM_PUSHPAGE …

   Differences between how paging is done on Solaris and Linux can cause
   deadlocks if KM_SLEEP is used in any the following contexts.
   
     * The z_wr_* threads
     * The txg_sync thread
     * The zvol write/discard threads
     * The zpl_putpage() VFS callback
   
   This is because KM_SLEEP will allow for direct reclaim which may result
   in the VM calling back in to the filesystem or block layer to write out
   pages.  If a lock is held over this operation the potential exists to
   deadlock the system.  To ensure forward progress all memory allocations
   in these contexts must us KM_PUSHPAGE which disables performing any I/O
   to accomplish the memory allocation.
   
   Previously, this behavior was acheived by setting PF_MEMALLOC on the
   thread.  However, that resulted in unexpected side effects such as the
   exhaustion of pages in ZONE_DMA.  This approach touchs more of the zfs
   code, but it is more consistent with the right way to handle these cases
   under Linux.
   
   This is patch lays the ground work for being able to safely revert the
   following commits which used PF_MEMALLOC:
   
     21ade34 Disable direct reclaim for z_wr_* threads
     cfc9a5c Fix zpl_writepage() deadlock
     eec8164 Fix ASSERTION(!dsl_pool_sync_context(tx->tx_pool))
   
   Signed-off-by: Richard Yao <ryao@cs.stonybrook.edu>
   Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
   Issue openzfs#726

   

   ryao committed Jun 29, 2012
   Copy the full SHA

   0aee477 View commit details

   Browse the repository at this point in the history