[PATCH 3/3] NFS/localio: issue commit inline when not in a memory-reclaim context

[Mike Snitzer]

Extend the memory-reclaim-context test used for LOCALIO reads and writes to
the commit (fsync) path.  As with data IO, bouncing every commit through the
dedicated !WQ_MEM_RECLAIM nfslocaliod_workqueue is only required when the
submitting context is a memory-reclaim context: nfs_local_run_commit() calls
vfs_fsync_range(), which may flush the underlying filesystem's own
!WQ_MEM_RECLAIM workqueue, and doing so from a WQ_MEM_RECLAIM worker or a
PF_MEMALLOC task trips check_flush_dependency().

The writeback path does exercise this: nfs_write_inode() (the ->write_inode
super_op) runs under wb_workfn on the WQ_MEM_RECLAIM bdi_wq and reaches
nfs_local_commit() via __nfs_commit_inode(), so that case must keep
deferring.  Application-context commits -- fsync (nfs_file_fsync), O_DIRECT
(nfs_direct), and copy/clone (nfs42) -- are not in a reclaim context and now
run the fsync inline via nfs_local_defer_io(), avoiding the per-commit
workqueue hop.

Completion (nfs_commit_release_pages -> nfs_commit_end) then runs
synchronously in the submitting context; higher layers already cope with
this, as __nfs_commit_inode() dispatches the commit async and waits for it
separately via wait_on_commit().

Assisted-by: Claude:claude-opus-4-8
Signed-off-by: Mike Snitzer <snitzer@xxxxxxxxxx>
---
 fs/nfs/localio.c | 14 +++++++++++++-
 1 file changed, 13 insertions(+), 1 deletion(-)

diff --git a/fs/nfs/localio.c b/fs/nfs/localio.c
index acbc2bddcf81..f42b6112a613 100644
--- a/fs/nfs/localio.c
+++ b/fs/nfs/localio.c
@@ -1132,7 +1132,19 @@ int nfs_local_commit(struct nfsd_file *localio,
 	}
 
 	nfs_local_init_commit(data, call_ops);
-	queue_work(nfslocaliod_workqueue, &ctx->work);
+
+	/*
+	 * Run the commit (fsync) inline when not in a memory-reclaim context,
+	 * rather than bouncing through nfslocaliod_workqueue; see
+	 * nfs_local_defer_io().  Completion (nfs_commit_release_pages ->
+	 * nfs_commit_end) then runs synchronously, which higher layers cope
+	 * with: __nfs_commit_inode() dispatches async and waits via
+	 * wait_on_commit().
+	 */
+	if (nfs_local_defer_io())
+		queue_work(nfslocaliod_workqueue, &ctx->work);
+	else
+		nfs_local_fsync_work(&ctx->work);
 
 	return 0;
 }
-- 
2.44.0