maple_tree: clarify comments on mas_nomem()

When an allocation completely fails, the return is false.  If the
allocation succeeds or partially succeeds, return true to indicate a retry
of the operation.  Note that since the lock may have been dropped, the
operation is retried from the start - including potentially allocating
more memory.

Link: https://lore.kernel.org/20260821192627.4085470-8-liam@infradead.org
Signed-off-by: Liam R. Howlett (Oracle) <liam@infradead.org>
Cc: Boqun Feng <boqun.feng@gmail.com>
Cc: Breno Leitao <leitao@debian.org>
Cc: Chris Mason <clm@meta.com>
Cc: Chuck Lever <cel@kernel.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Jason Gunthorpe <jgg@ziepe.ca>
Cc: Joe Perches <joe@perches.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Rik van Riel <riel@surriel.com>
Cc: Waiman Long <longman@redhat.com>
Cc: Will Deacon <will@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

lib/maple_tree.c

@@ -5677,10 +5677,11 @@ EXPORT_SYMBOL_GPL(mas_erase);
 
 /**
  * mas_nomem() - Check if there was an error allocating and do the allocation
- * if necessary If there are allocations, then free them.
+ * if necessary.
+ *
  * @mas: The maple state
  * @gfp: The GFP_FLAGS to use for allocations
- * Return: true on allocation, false otherwise.
+ * Return: False on no memory.  True otherwise (partial success as well)
  */
 bool mas_nomem(struct ma_state *mas, gfp_t gfp)
 	__must_hold(mas->tree->ma_lock)
@@ -5696,6 +5697,10 @@ bool mas_nomem(struct ma_state *mas, gfp_t gfp)
 		mas_alloc_nodes(mas, gfp);
 	}
 
+	/*
+	 * Return false on zero forward progress.  Partial allocations are kept
+	 * so the retry path will attempt to get the rest.
+	 */
 	if (!mas->sheaf && !mas->alloc)
 		return false;