diff mbox series

[v2] malloc: Remove bin scanning from memalign (bug 30723)

Message ID 87r0o9x6gz.fsf@oldenburg.str.redhat.com
State New
Headers show
Series [v2] malloc: Remove bin scanning from memalign (bug 30723) | expand

Commit Message

Florian Weimer Aug. 11, 2023, 9:40 a.m. UTC
On the test workload (mpv --cache=yes with VP9 video decoding), the
bin scanning has a very poor success rate (less than 2%).  The tcache
scanning has about 50% success rate, so keep that.

Remove the part of malloc/tst-memalign-2 that is supposedly exercise
bin scanning (supposedly because on x86-64, removing the bin scanning
does not cause this part to fail).

---
v2: Remove the bin scanning part of malloc/tst-memalign-2.
 malloc/malloc.c         | 127 ++----------------------------------------------
 malloc/tst-memalign-2.c |  53 --------------------
 2 files changed, 5 insertions(+), 175 deletions(-)


base-commit: 542b1105852568c3ebc712225ae78b8c8ba31a78
diff mbox series

Patch

diff --git a/malloc/malloc.c b/malloc/malloc.c
index 948f9759af..9c2cab7a59 100644
--- a/malloc/malloc.c
+++ b/malloc/malloc.c
@@ -5082,7 +5082,6 @@  _int_memalign (mstate av, size_t alignment, size_t bytes)
   mchunkptr remainder;            /* spare room at end to split off */
   unsigned long remainder_size;   /* its size */
   INTERNAL_SIZE_T size;
-  mchunkptr victim;
 
   nb = checked_request2size (bytes);
   if (nb == 0)
@@ -5101,129 +5100,13 @@  _int_memalign (mstate av, size_t alignment, size_t bytes)
      we don't find anything in those bins, the common malloc code will
      scan starting at 2x.  */
 
-  /* This will be set if we found a candidate chunk.  */
-  victim = NULL;
+  /* Call malloc with worst case padding to hit alignment. */
+  m = (char *) (_int_malloc (av, nb + alignment + MINSIZE));
 
-  /* Fast bins are singly-linked, hard to remove a chunk from the middle
-     and unlikely to meet our alignment requirements.  We have not done
-     any experimentation with searching for aligned fastbins.  */
+  if (m == 0)
+    return 0;           /* propagate failure */
 
-  if (av != NULL)
-    {
-      int first_bin_index;
-      int first_largebin_index;
-      int last_bin_index;
-
-      if (in_smallbin_range (nb))
-	first_bin_index = smallbin_index (nb);
-      else
-	first_bin_index = largebin_index (nb);
-
-      if (in_smallbin_range (nb * 2))
-	last_bin_index = smallbin_index (nb * 2);
-      else
-	last_bin_index = largebin_index (nb * 2);
-
-      first_largebin_index = largebin_index (MIN_LARGE_SIZE);
-
-      int victim_index;                 /* its bin index */
-
-      for (victim_index = first_bin_index;
-	   victim_index < last_bin_index;
-	   victim_index ++)
-	{
-	  victim = NULL;
-
-	  if (victim_index < first_largebin_index)
-	    {
-	      /* Check small bins.  Small bin chunks are doubly-linked despite
-		 being the same size.  */
-
-	      mchunkptr fwd;                    /* misc temp for linking */
-	      mchunkptr bck;                    /* misc temp for linking */
-
-	      bck = bin_at (av, victim_index);
-	      fwd = bck->fd;
-	      while (fwd != bck)
-		{
-		  if (chunk_ok_for_memalign (fwd, alignment, nb) > 0)
-		    {
-		      victim = fwd;
-
-		      /* Unlink it */
-		      victim->fd->bk = victim->bk;
-		      victim->bk->fd = victim->fd;
-		      break;
-		    }
-
-		  fwd = fwd->fd;
-		}
-	    }
-	  else
-	    {
-	      /* Check large bins.  */
-	      mchunkptr fwd;                    /* misc temp for linking */
-	      mchunkptr bck;                    /* misc temp for linking */
-	      mchunkptr best = NULL;
-	      size_t best_size = 0;
-
-	      bck = bin_at (av, victim_index);
-	      fwd = bck->fd;
-
-	      while (fwd != bck)
-		{
-		  int extra;
-
-		  if (chunksize (fwd) < nb)
-		    break;
-		  extra = chunk_ok_for_memalign (fwd, alignment, nb);
-		  if (extra > 0
-		      && (extra <= best_size || best == NULL))
-		    {
-		      best = fwd;
-		      best_size = extra;
-		    }
-
-		  fwd = fwd->fd;
-		}
-	      victim = best;
-
-	      if (victim != NULL)
-		{
-		  unlink_chunk (av, victim);
-		  break;
-		}
-	    }
-
-	  if (victim != NULL)
-	    break;
-	}
-    }
-
-  /* Strategy: find a spot within that chunk that meets the alignment
-     request, and then possibly free the leading and trailing space.
-     This strategy is incredibly costly and can lead to external
-     fragmentation if header and footer chunks are unused.  */
-
-  if (victim != NULL)
-    {
-      p = victim;
-      m = chunk2mem (p);
-      set_inuse (p);
-      if (av != &main_arena)
-	set_non_main_arena (p);
-    }
-  else
-    {
-      /* Call malloc with worst case padding to hit alignment. */
-
-      m = (char *) (_int_malloc (av, nb + alignment + MINSIZE));
-
-      if (m == 0)
-	return 0;           /* propagate failure */
-
-      p = mem2chunk (m);
-    }
+  p = mem2chunk (m);
 
   if ((((unsigned long) (m)) % alignment) != 0)   /* misaligned */
     {
diff --git a/malloc/tst-memalign-2.c b/malloc/tst-memalign-2.c
index f229283dbf..a99fb2c6d3 100644
--- a/malloc/tst-memalign-2.c
+++ b/malloc/tst-memalign-2.c
@@ -40,18 +40,6 @@  static TestCase tcache_allocs[] = {
 };
 #define TN array_length (tcache_allocs)
 
-static TestCase large_allocs[] = {
-  { 23450, 64, NULL, NULL },
-  { 23450, 64, NULL, NULL },
-  { 23550, 64, NULL, NULL },
-  { 23550, 64, NULL, NULL },
-  { 23650, 64, NULL, NULL },
-  { 23650, 64, NULL, NULL },
-  { 33650, 64, NULL, NULL },
-  { 33650, 64, NULL, NULL }
-};
-#define LN array_length (large_allocs)
-
 void *p;
 
 /* Sanity checks, ancillary to the actual test.  */
@@ -113,47 +101,6 @@  do_test (void)
   free (p);
   TEST_VERIFY (count > 0);
 
-  /* Large bins test.  */
-
-  for (i = 0; i < LN; ++ i)
-    {
-      large_allocs[i].ptr1 = memalign (large_allocs[i].alignment, large_allocs[i].size);
-      CHECK (large_allocs[i].ptr1, large_allocs[i].alignment);
-      /* Keep chunks from combining by fragmenting the heap.  */
-      p = malloc (512);
-      CHECK (p, 4);
-    }
-
-  for (i = 0; i < LN; ++ i)
-    free (large_allocs[i].ptr1);
-
-  /* Force the unsorted bins to be scanned and moved to small/large
-     bins.  */
-  p = malloc (60000);
-
-  for (i = 0; i < LN; ++ i)
-    {
-      large_allocs[i].ptr2 = memalign (large_allocs[i].alignment, large_allocs[i].size);
-      CHECK (large_allocs[i].ptr2, large_allocs[i].alignment);
-    }
-
-  count = 0;
-  for (i = 0; i < LN; ++ i)
-    {
-      int ok = 0;
-      for (j = 0; j < LN; ++ j)
-	if (large_allocs[i].ptr1 == large_allocs[j].ptr2)
-	  ok = 1;
-      if (ok == 1)
-	count ++;
-    }
-
-  /* The allocation algorithm is complicated outside of the memalign
-     logic, so just make sure it's working for most of the
-     allocations.  This avoids possible boundary conditions with
-     empty/full heaps.  */
-  TEST_VERIFY (count > LN / 2);
-
   return 0;
 }