1 files changed, 81 insertions, 1 deletions

diff --git a/fs/xfs/xfs_btree.c b/fs/xfs/xfs_btree.c
index bf810c6baf2b..cf893bc1e373 100644
--- a/fs/xfs/xfs_btree.c
+++ b/fs/xfs/xfs_btree.c
@@ -33,6 +33,7 @@
 #include "xfs_error.h"
 #include "xfs_trace.h"
 #include "xfs_cksum.h"
+#include "xfs_alloc.h"
 
 /*
  * Cursor allocation zone.
@@ -2323,7 +2324,7 @@ error1:
  * record (to be inserted into parent).
  */
 STATIC int                                      /* error */
-xfs_btree_split(
+__xfs_btree_split(
         struct xfs_btree_cur    *cur,
         int                     level,
         union xfs_btree_ptr     *ptrp,
@@ -2503,6 +2504,85 @@ error0:
         return error;
 }
 
+struct xfs_btree_split_args {
+        struct xfs_btree_cur    *cur;
+        int                     level;
+        union xfs_btree_ptr     *ptrp;
+        union xfs_btree_key     *key;
+        struct xfs_btree_cur    **curp;
+        int                     *stat;          /* success/failure */
+        int                     result;
+        bool                    kswapd; /* allocation in kswapd context */
+        struct completion       *done;
+        struct work_struct      work;
+};
+
+/*
+ * Stack switching interfaces for allocation
+ */
+static void
+xfs_btree_split_worker(
+        struct work_struct      *work)
+{
+        struct xfs_btree_split_args     *args = container_of(work,
+                                                struct xfs_btree_split_args, work);
+        unsigned long           pflags;
+        unsigned long           new_pflags = PF_FSTRANS;
+
+        /*
+         * we are in a transaction context here, but may also be doing work
+         * in kswapd context, and hence we may need to inherit that state
+         * temporarily to ensure that we don't block waiting for memory reclaim
+         * in any way.
+         */
+        if (args->kswapd)
+                new_pflags |= PF_MEMALLOC | PF_SWAPWRITE | PF_KSWAPD;
+
+        current_set_flags_nested(&pflags, new_pflags);
+
+        args->result = __xfs_btree_split(args->cur, args->level, args->ptrp,
+                                         args->key, args->curp, args->stat);
+        complete(args->done);
+
+        current_restore_flags_nested(&pflags, new_pflags);
+}
+
+/*
+ * BMBT split requests often come in with little stack to work on. Push
+ * them off to a worker thread so there is lots of stack to use. For the other
+ * btree types, just call directly to avoid the context switch overhead here.
+ */
+STATIC int                                      /* error */
+xfs_btree_split(
+        struct xfs_btree_cur    *cur,
+        int                     level,
+        union xfs_btree_ptr     *ptrp,
+        union xfs_btree_key     *key,
+        struct xfs_btree_cur    **curp,
+        int                     *stat)          /* success/failure */
+{
+        struct xfs_btree_split_args     args;
+        DECLARE_COMPLETION_ONSTACK(done);
+
+        if (cur->bc_btnum != XFS_BTNUM_BMAP)
+                return __xfs_btree_split(cur, level, ptrp, key, curp, stat);
+
+        args.cur = cur;
+        args.level = level;
+        args.ptrp = ptrp;
+        args.key = key;
+        args.curp = curp;
+        args.stat = stat;
+        args.done = &done;
+        args.kswapd = current_is_kswapd();
+        INIT_WORK_ONSTACK(&args.work, xfs_btree_split_worker);
+        queue_work(xfs_alloc_wq, &args.work);
+        wait_for_completion(&done);
+        destroy_work_on_stack(&args.work);
+        return args.result;
+}
+
+
 /*
  * Copy the old inode root contents into a real block and make the
  * broot point to it.