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Currently AGFL blocks can be filled from the following three sources:
- allocbt free blocks, as in xfs_allocbt_free_block();
- rmapbt free blocks, as in xfs_rmapbt_free_block();
- refilled from freespace btrees, as in xfs_alloc_fix_freelist().
Originally, allocbt free blocks would be marked as stale only when they
put back in the general free space pool as Dave mentioned on IRC, "we
don't stale AGF metadata btree blocks when they are returned to the
AGFL .. but once they get put back in the general free space pool, we
have to make sure the buffers are marked stale as the next user of
those blocks might be user data...."
However, after commit ca250b1b3d71 ("xfs: invalidate allocbt blocks
moved to the free list") and commit edfd9dd54921 ("xfs: move buffer
invalidation to xfs_btree_free_block"), even allocbt / bmapbt free
blocks will be invalidated immediately since they may fail to pass
V5 format validation on writeback even writeback to free space would be
safe.
IOWs, IMHO currently there is actually no difference of free blocks
between AGFL freespace pool and the general free space pool. So let's
avoid extra redundant AGFL buffer invalidation, since otherwise we're
currently facing unnecessary xfs_log_force() due to xfs_trans_binval()
again on buffers already marked as stale before as below:
[ 333.507469] Call Trace:
[ 333.507862] xfs_buf_find+0x371/0x6a0 <- xfs_buf_lock
[ 333.508451] xfs_buf_get_map+0x3f/0x230
[ 333.509062] xfs_trans_get_buf_map+0x11a/0x280
[ 333.509751] xfs_free_agfl_block+0xa1/0xd0
[ 333.510403] xfs_agfl_free_finish_item+0x16e/0x1d0
[ 333.511157] xfs_defer_finish_noroll+0x1ef/0x5c0
[ 333.511871] xfs_defer_finish+0xc/0xa0
[ 333.512471] xfs_itruncate_extents_flags+0x18a/0x5e0
[ 333.513253] xfs_inactive_truncate+0xb8/0x130
[ 333.513930] xfs_inactive+0x223/0x270
xfs_log_force() will take tens of milliseconds with AGF buffer locked.
It becomes an unnecessary long latency especially on our PMEM devices
with FSDAX enabled and fsops like xfs_reflink_find_shared() at the same
time are stuck due to the same AGF lock. Removing the double
invalidation on the AGFL blocks does not make this issue go away, but
this patch fixes for our workloads in reality and it should also work
by the code analysis.
Note that I'm not sure I need to remove another redundant one in
xfs_alloc_ag_vextent_small() since it's unrelated to our workloads.
Also fstests are passed with this patch.
Signed-off-by: Gao Xiang <hsiangkao@linux.alibaba.com>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Signed-off-by: Chandan Babu R <chandanbabu@kernel.org>
d40c2865bd