6.1-stable review patch. If anyone has any objections, please let me know.
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From: Mike Snitzer snitzer@kernel.org
[ Upstream commit 867da60d463bb2a3e28c9235c487e56e96cffa00 ]
Multi-threaded buffered reads to the same file exposed significant inode spinlock contention in nfs_clear_invalid_mapping().
Eliminate this spinlock contention by checking flags without locking, instead using smp_rmb and smp_load_acquire accordingly, but then take spinlock and double-check these inode flags.
Also refactor nfs_set_cache_invalid() slightly to use smp_store_release() to pair with nfs_clear_invalid_mapping()'s smp_load_acquire().
While this fix is beneficial for all multi-threaded buffered reads issued by an NFS client, this issue was identified in the context of surprisingly low LOCALIO performance with 4K multi-threaded buffered read IO. This fix dramatically speeds up LOCALIO performance:
before: read: IOPS=1583k, BW=6182MiB/s (6482MB/s)(121GiB/20002msec) after: read: IOPS=3046k, BW=11.6GiB/s (12.5GB/s)(232GiB/20001msec)
Fixes: 17dfeb911339 ("NFS: Fix races in nfs_revalidate_mapping") Signed-off-by: Mike Snitzer snitzer@kernel.org Reviewed-by: Jeff Layton jlayton@kernel.org Signed-off-by: Anna Schumaker anna.schumaker@oracle.com Signed-off-by: Sasha Levin sashal@kernel.org --- fs/nfs/inode.c | 20 +++++++++++++++----- 1 file changed, 15 insertions(+), 5 deletions(-)
diff --git a/fs/nfs/inode.c b/fs/nfs/inode.c index 82e846611d5e1..719448d81aed2 100644 --- a/fs/nfs/inode.c +++ b/fs/nfs/inode.c @@ -206,12 +206,15 @@ void nfs_set_cache_invalid(struct inode *inode, unsigned long flags) nfs_fscache_invalidate(inode, 0); flags &= ~NFS_INO_REVAL_FORCED;
- nfsi->cache_validity |= flags; + flags |= nfsi->cache_validity; + if (inode->i_mapping->nrpages == 0) + flags &= ~NFS_INO_INVALID_DATA;
- if (inode->i_mapping->nrpages == 0) { - nfsi->cache_validity &= ~NFS_INO_INVALID_DATA; - nfs_ooo_clear(nfsi); - } else if (nfsi->cache_validity & NFS_INO_INVALID_DATA) { + /* pairs with nfs_clear_invalid_mapping()'s smp_load_acquire() */ + smp_store_release(&nfsi->cache_validity, flags); + + if (inode->i_mapping->nrpages == 0 || + nfsi->cache_validity & NFS_INO_INVALID_DATA) { nfs_ooo_clear(nfsi); } trace_nfs_set_cache_invalid(inode, 0); @@ -1331,6 +1334,13 @@ int nfs_clear_invalid_mapping(struct address_space *mapping) TASK_KILLABLE|TASK_FREEZABLE_UNSAFE); if (ret) goto out; + smp_rmb(); /* pairs with smp_wmb() below */ + if (test_bit(NFS_INO_INVALIDATING, bitlock)) + continue; + /* pairs with nfs_set_cache_invalid()'s smp_store_release() */ + if (!(smp_load_acquire(&nfsi->cache_validity) & NFS_INO_INVALID_DATA)) + goto out; + /* Slow-path that double-checks with spinlock held */ spin_lock(&inode->i_lock); if (test_bit(NFS_INO_INVALIDATING, bitlock)) { spin_unlock(&inode->i_lock);