Alas, mvff and mvt can't round up alignment because they need to support buffered allocation.

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 Change: 185381
 ServerID: perforce.ravenbrook.com

mps/code/poolmv2.c

@@ -254,6 +254,11 @@ static Res MVTInit(Pool pool, ArgList args)
   }
 
   AVERT(Align, align);
+  /* This restriction on the alignment is necessary because of the use
+   * of a Freelist to store the free address ranges in low-memory
+   * situations. See <design/freelist/#impl.grain.align>.
+   */
+  AVER(AlignIsAligned(align, FreelistMinimumAlignment));
   AVER(0 < minSize);
   AVER(minSize <= meanSize);
   AVER(meanSize <= maxSize);
@@ -261,12 +266,6 @@ static Res MVTInit(Pool pool, ArgList args)
   AVER(fragLimit <= 100);
   /* TODO: More sanity checks possible? */
 
-  /* This restriction on the alignment is necessary because of the use
-   * of a Freelist to store the free address ranges in low-memory
-   * situations. See <design/freelist/#impl.grain.align>.
-   */
-  align = AlignAlignUp(align, FreelistMinimumAlignment);
-
   /* see <design/poolmvt/#arch.parameters> */
   fillSize = SizeAlignUp(maxSize, ArenaAlign(arena));
   /* see <design/poolmvt/#arch.fragmentation.internal> */

mps/code/poolmvff.c

@@ -571,15 +571,14 @@ static Res MVFFInit(Pool pool, ArgList args)
   AVER(avgSize > 0);            /* .arg.check */
   AVER(avgSize <= extendBy);    /* .arg.check */
   AVERT(Align, align);
-  AVERT(Bool, slotHigh);
-  AVERT(Bool, arenaHigh);
-  AVERT(Bool, firstFit);
-
   /* This restriction on the alignment is necessary because of the use
    * of a Freelist to store the free address ranges in low-memory
    * situations. <design/freelist/#impl.grain.align>.
    */
-  align = AlignAlignUp(align, FreelistMinimumAlignment);
+  AVER(AlignIsAligned(align, FreelistMinimumAlignment));
+  AVERT(Bool, slotHigh);
+  AVERT(Bool, arenaHigh);
+  AVERT(Bool, firstFit);
 
   mvff = Pool2MVFF(pool);
 

mps/manual/source/pool/intro.rst

@@ -156,8 +156,8 @@ Blocks may use :term:`in-band headers`?        yes    yes    yes    yes    yes
            :c:macro:`MPS_PF_ALIGN`.
 
     .. [7] :ref:`pool-mvt` and :ref:`pool-mvff` pools have
-           configurable alignment, but smaller values than
-           ``sizeof(void *)`` are rounded up.
+           configurable alignment, but it may not be smaller than
+           ``sizeof(void *)``.
 
     .. [8] In pools with this property, each object may specify an
            :term:`dependent object` which the client program

mps/manual/source/pool/mvff.rst

@@ -79,8 +79,8 @@ MVFF properties
 
 * Allocations may be variable in size.
 
-* The :term:`alignment` of blocks is configurable, but smaller
-  alignments than ``sizeof(void *)`` are rounded up.
+* The :term:`alignment` of blocks is configurable, but may not be
+  smaller than ``sizeof(void *)``.
 
 * Blocks do not have :term:`dependent objects`.
 
@@ -130,8 +130,7 @@ MVFF interface
       the pool. If an unaligned size is passed to :c:func:`mps_alloc`
       or :c:func:`mps_free`, it will be rounded up to the pool's
       alignment. The minimum alignment supported by pools of this
-      class is ``sizeof(void *)``; you can pass a smaller alignment
-      but it will be rounded up.
+      class is ``sizeof(void *)``.
 
     * :c:macro:`MPS_KEY_MVFF_ARENA_HIGH` (type :c:type:`mps_bool_t`,
       default false) determines whether new segments are acquired at high

mps/manual/source/pool/mvt.rst

@@ -78,8 +78,8 @@ MVT properties
 
 * Allocations may be variable in size.
 
-* The :term:`alignment` of blocks is configurable, but smaller
-  alignments than ``sizeof(void *)`` are rounded up.
+* The :term:`alignment` of blocks is configurable, but may not be
+  smaller than ``sizeof(void *)``.
 
 * Blocks do not have :term:`dependent objects`.
 
@@ -120,8 +120,7 @@ MVT interface
       the pool. If an unaligned size is passed to :c:func:`mps_alloc` or
       :c:func:`mps_free`, it will be rounded up to the pool's alignment.
       The minimum alignment supported by pools of this class is
-      ``sizeof(void *)``; you can pass a smaller alignment but it will
-      be rounded up.
+      ``sizeof(void *)``.
 
     * :c:macro:`MPS_KEY_MIN_SIZE` (type :c:type:`size_t`, default is
       :c:macro:`MPS_PF_ALIGN`) is the

mps/manual/source/release.rst

@@ -34,13 +34,10 @@ Interface changes
    in a :ref:`pool-mv` pool, by passing the :c:macro:`MPS_KEY_ALIGN`
    keyword argument to :c:func:`mps_pool_create_k`.
 
-#. It is now possible to specify any alignment for :ref:`pool-mvff`
-   and :ref:`pool-mvt` pools. Alignments smaller than
-   ``sizeof(void *)`` are rounded up automatically. This means that on
-   the platforms ``w3i3mv`` and ``w3i6mv``, where
-   :c:macro:`MPS_PF_ALIGN` is larger than ``sizeof(void *)``, it is
-   now possible to specify the latter as the alignment for these
-   pools.
+#. The alignment requirements for :ref:`pool-mvff` and :ref:`pool-mvt`
+   pools have been relaxed on the platforms ``w3i3mv`` and ``w3i6mv``.
+   On all platforms it is now possible to specify alignments down to
+   ``sizeof(void *)`` as the alignment for pools of these classes.
 
 
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