xfs: convert xfs_alloc_vextent_iterate_ags() to use perag walker

Now that the AG iteration code in the core allocation code has been
cleaned up, we can easily convert it to use a for_each_perag..()
variant to use active references and skip AGs that it can't get
active references on.

Signed-off-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Darrick J. Wong <djwong@kernel.org>

diff --git a/fs/xfs/libxfs/xfs_ag.h b/fs/xfs/libxfs/xfs_ag.h
index 8f43b91..5e18536 100644 (file)
--- a/fs/xfs/libxfs/xfs_ag.h
+++ b/fs/xfs/libxfs/xfs_ag.h
@@ -253,6 +253,7 @@ xfs_perag_next_wrap(
        struct xfs_perag        *pag,
        xfs_agnumber_t          *agno,
        xfs_agnumber_t          stop_agno,
+       xfs_agnumber_t          restart_agno,
        xfs_agnumber_t          wrap_agno)
 {
        struct xfs_mount        *mp = pag->pag_mount;
@@ -260,10 +261,11 @@ xfs_perag_next_wrap(
        *agno = pag->pag_agno + 1;
        xfs_perag_rele(pag);
        while (*agno != stop_agno) {
-               if (*agno >= wrap_agno)
-                       *agno = 0;
-               if (*agno == stop_agno)
-                       break;
+               if (*agno >= wrap_agno) {
+                       if (restart_agno >= stop_agno)
+                               break;
+                       *agno = restart_agno;
+               }
 
                pag = xfs_perag_grab(mp, *agno);
                if (pag)
@@ -274,14 +276,20 @@ xfs_perag_next_wrap(
 }
 
 /*
- * Iterate all AGs from start_agno through wrap_agno, then 0 through
+ * Iterate all AGs from start_agno through wrap_agno, then restart_agno through
  * (start_agno - 1).
  */
-#define for_each_perag_wrap_at(mp, start_agno, wrap_agno, agno, pag) \
+#define for_each_perag_wrap_range(mp, start_agno, restart_agno, wrap_agno, agno, pag) \
        for ((agno) = (start_agno), (pag) = xfs_perag_grab((mp), (agno)); \
                (pag) != NULL; \
                (pag) = xfs_perag_next_wrap((pag), &(agno), (start_agno), \
-                               (wrap_agno)))
+                               (restart_agno), (wrap_agno)))
+/*
+ * Iterate all AGs from start_agno through wrap_agno, then 0 through
+ * (start_agno - 1).
+ */
+#define for_each_perag_wrap_at(mp, start_agno, wrap_agno, agno, pag) \
+       for_each_perag_wrap_range((mp), (start_agno), 0, (wrap_agno), (agno), (pag))
 
 /*
  * Iterate all AGs from start_agno through to the end of the filesystem, then 0

diff --git a/fs/xfs/libxfs/xfs_alloc.c b/fs/xfs/libxfs/xfs_alloc.c
index 94cea96..6a03717 100644 (file)
--- a/fs/xfs/libxfs/xfs_alloc.c
+++ b/fs/xfs/libxfs/xfs_alloc.c
@@ -3156,6 +3156,7 @@ xfs_alloc_vextent_prepare_ag(
        if (need_pag)
                args->pag = xfs_perag_get(args->mp, args->agno);
 
+       args->agbp = NULL;
        error = xfs_alloc_fix_freelist(args, 0);
        if (error) {
                trace_xfs_alloc_vextent_nofix(args);
@@ -3255,8 +3256,8 @@ xfs_alloc_vextent_finish(
        XFS_STATS_ADD(mp, xs_allocb, args->len);
 
 out_drop_perag:
-       if (drop_perag) {
-               xfs_perag_put(args->pag);
+       if (drop_perag && args->pag) {
+               xfs_perag_rele(args->pag);
                args->pag = NULL;
        }
        return error;
@@ -3304,6 +3305,10 @@ xfs_alloc_vextent_this_ag(
  * we attempt to allocation in as there is no locality optimisation possible for
  * those allocations.
  *
+ * On return, args->pag may be left referenced if we finish before the "all
+ * failed" return point. The allocation finish still needs the perag, and
+ * so the caller will release it once they've finished the allocation.
+ *
  * When we wrap the AG iteration at the end of the filesystem, we have to be
  * careful not to wrap into AGs below ones we already have locked in the
  * transaction if we are doing a blocking iteration. This will result in an
@@ -3318,72 +3323,55 @@ xfs_alloc_vextent_iterate_ags(
        uint32_t                flags)
 {
        struct xfs_mount        *mp = args->mp;
+       xfs_agnumber_t          agno;
        int                     error = 0;
 
-       ASSERT(start_agno >= minimum_agno);
-
-       /*
-        * Loop over allocation groups twice; first time with
-        * trylock set, second time without.
-        */
-       args->agno = start_agno;
-       for (;;) {
-               args->pag = xfs_perag_get(mp, args->agno);
+restart:
+       for_each_perag_wrap_range(mp, start_agno, minimum_agno,
+                       mp->m_sb.sb_agcount, agno, args->pag) {
+               args->agno = agno;
                error = xfs_alloc_vextent_prepare_ag(args);
                if (error)
                        break;
-
-               if (args->agbp) {
-                       /*
-                        * Allocation is supposed to succeed now, so break out
-                        * of the loop regardless of whether we succeed or not.
-                        */
-                       if (args->agno == start_agno && target_agbno) {
-                               args->agbno = target_agbno;
-                               error = xfs_alloc_ag_vextent_near(args);
-                       } else {
-                               args->agbno = 0;
-                               error = xfs_alloc_ag_vextent_size(args);
-                       }
-                       break;
-               }
-
-               trace_xfs_alloc_vextent_loopfailed(args);
-
-               /*
-                * If we are try-locking, we can't deadlock on AGF locks so we
-                * can wrap all the way back to the first AG. Otherwise, wrap
-                * back to the start AG so we can't deadlock and let the end of
-                * scan handler decide what to do next.
-                */
-               if (++(args->agno) == mp->m_sb.sb_agcount) {
-                       if (flags & XFS_ALLOC_FLAG_TRYLOCK)
-                               args->agno = 0;
-                       else
-                               args->agno = minimum_agno;
+               if (!args->agbp) {
+                       trace_xfs_alloc_vextent_loopfailed(args);
+                       continue;
                }
 
                /*
-                * Reached the starting a.g., must either be done
-                * or switch to non-trylock mode.
+                * Allocation is supposed to succeed now, so break out of the
+                * loop regardless of whether we succeed or not.
                 */
-               if (args->agno == start_agno) {
-                       if (flags == 0) {
-                               args->agbno = NULLAGBLOCK;
-                               trace_xfs_alloc_vextent_allfailed(args);
-                               break;
-                       }
+               if (args->agno == start_agno && target_agbno) {
                        args->agbno = target_agbno;
-                       flags = 0;
+                       error = xfs_alloc_ag_vextent_near(args);
+               } else {
+                       args->agbno = 0;
+                       error = xfs_alloc_ag_vextent_size(args);
                }
-               xfs_perag_put(args->pag);
+               break;
+       }
+       if (error) {
+               xfs_perag_rele(args->pag);
                args->pag = NULL;
+               return error;
        }
+       if (args->agbp)
+               return 0;
+
        /*
-        * The perag is left referenced in args for the caller to clean
-        * up after they've finished the allocation.
+        * We didn't find an AG we can alloation from. If we were given
+        * constraining flags by the caller, drop them and retry the allocation
+        * without any constraints being set.
         */
-       return error;
+       if (flags) {
+               flags = 0;
+               goto restart;
+       }
+
+       ASSERT(args->pag == NULL);
+       trace_xfs_alloc_vextent_allfailed(args);
+       return 0;
 }
 
 /*
@@ -3524,7 +3512,7 @@ xfs_alloc_vextent_near_bno(
        }
 
        if (needs_perag)
-               args->pag = xfs_perag_get(mp, args->agno);
+               args->pag = xfs_perag_grab(mp, args->agno);
 
        error = xfs_alloc_vextent_prepare_ag(args);
        if (!error && args->agbp)