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mlx4_core: Avoid recycling old FMR R_Keys too soon

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When a FMR is unmapped, mlx4 resets the map count to 0, and clears the
upper part of the R_Key which is used as the sequence counter.

This poses a problem for RDS, which uses ib_fmr_unmap as a fence
operation.  RDS assumes that after issuing an unmap, the old R_Keys
will be invalid for a "reasonable" period of time. For instance,
Oracle processes uses shared memory buffers allocated from a pool of
buffers.  When a process dies, we want to reclaim these buffers -- but
we must make sure there are no pending RDMA operations to/from those
buffers.  The only way to achieve that is by using unmap and sync the
TPT.

However, when the sequence count is reset on unmap, there is a high
likelihood that a new mapping will be given the same R_Key that was
issued a few milliseconds ago.

To prevent this, don't reset the sequence count when unmapping a FMR.

Signed-off-by: Olaf Kirch <olaf.kirch@oracle.com>
Signed-off-by: Roland Dreier <rolandd@cisco.com>
This commit is contained in:
Olaf Kirch 2008-04-29 13:46:53 -07:00 committed by Roland Dreier
parent d227fa7288
commit bbdc2821db
1 changed files with 0 additions and 6 deletions
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6
drivers/net/mlx4/mr.c
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@ -607,15 +607,9 @@ EXPORT_SYMBOL_GPL(mlx4_fmr_enable);
void mlx4_fmr_unmap(struct mlx4_dev *dev, struct mlx4_fmr *fmr,
u32 *lkey, u32 *rkey)
{
u32 key;
if (!fmr->maps)
return;
key = key_to_hw_index(fmr->mr.key);
key &= dev->caps.num_mpts - 1;
*lkey = *rkey = fmr->mr.key = hw_index_to_key(key);
fmr->maps = 0;
*(u8 *) fmr->mpt = MLX4_MPT_STATUS_SW;