jobcore/glibc/fix-malloc-p2.patch
2023-08-17 23:50:49 +03:00

249 lines
7.6 KiB
Diff

commit 0dc7fc1cf094406a138e4d1bcf9553e59edcf89d
Author: Florian Weimer <fweimer@redhat.com>
Date: Thu Aug 10 19:36:56 2023 +0200
malloc: Remove bin scanning from memalign (bug 30723)
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.
Update comments in malloc/tst-memalign-2 to indicate the purpose
of the tests. Even with the scanning removed, the additional
merging opportunities since commit 542b1105852568c3ebc712225ae78b
("malloc: Enable merging of remainders in memalign (bug 30723)")
are sufficient to pass the existing large bins test.
Remove leftover variables from _int_free from refactoring in the
same commit.
Reviewed-by: DJ Delorie <dj@redhat.com>
diff --git a/malloc/malloc.c b/malloc/malloc.c
index 948f9759af..d0bbbf3710 100644
--- a/malloc/malloc.c
+++ b/malloc/malloc.c
@@ -4488,12 +4488,6 @@ _int_free (mstate av, mchunkptr p, int have_lock)
{
INTERNAL_SIZE_T size; /* its size */
mfastbinptr *fb; /* associated fastbin */
- mchunkptr nextchunk; /* next contiguous chunk */
- INTERNAL_SIZE_T nextsize; /* its size */
- int nextinuse; /* true if nextchunk is used */
- INTERNAL_SIZE_T prevsize; /* size of previous contiguous chunk */
- mchunkptr bck; /* misc temp for linking */
- mchunkptr fwd; /* misc temp for linking */
size = chunksize (p);
@@ -5032,42 +5026,6 @@ _int_realloc (mstate av, mchunkptr oldp, INTERNAL_SIZE_T oldsize,
------------------------------ memalign ------------------------------
*/
-/* Returns 0 if the chunk is not and does not contain the requested
- aligned sub-chunk, else returns the amount of "waste" from
- trimming. NB is the *chunk* byte size, not the user byte
- size. */
-static size_t
-chunk_ok_for_memalign (mchunkptr p, size_t alignment, size_t nb)
-{
- void *m = chunk2mem (p);
- INTERNAL_SIZE_T size = chunksize (p);
- void *aligned_m = m;
-
- if (__glibc_unlikely (misaligned_chunk (p)))
- malloc_printerr ("_int_memalign(): unaligned chunk detected");
-
- aligned_m = PTR_ALIGN_UP (m, alignment);
-
- INTERNAL_SIZE_T front_extra = (intptr_t) aligned_m - (intptr_t) m;
-
- /* We can't trim off the front as it's too small. */
- if (front_extra > 0 && front_extra < MINSIZE)
- return 0;
-
- /* If it's a perfect fit, it's an exception to the return value rule
- (we would return zero waste, which looks like "not usable"), so
- handle it here by returning a small non-zero value instead. */
- if (size == nb && front_extra == 0)
- return 1;
-
- /* If the block we need fits in the chunk, calculate total waste. */
- if (size > nb + front_extra)
- return size - nb;
-
- /* Can't use this chunk. */
- return 0;
-}
-
/* BYTES is user requested bytes, not requested chunksize bytes. */
static void *
_int_memalign (mstate av, size_t alignment, size_t bytes)
@@ -5082,7 +5040,6 @@ _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 +5058,13 @@ _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;
-
- /* 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 (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;
+ /* Call malloc with worst case padding to hit alignment. */
+ m = (char *) (_int_malloc (av, nb + alignment + MINSIZE));
- 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;
- }
+ if (m == 0)
+ return 0; /* propagate failure */
- 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..ecd6fa249e 100644
--- a/malloc/tst-memalign-2.c
+++ b/malloc/tst-memalign-2.c
@@ -86,7 +86,8 @@ do_test (void)
TEST_VERIFY (tcache_allocs[i].ptr1 == tcache_allocs[i].ptr2);
}
- /* Test for non-head tcache hits. */
+ /* Test for non-head tcache hits. This exercises the memalign
+ scanning code to find matching allocations. */
for (i = 0; i < array_length (ptr); ++ i)
{
if (i == 4)
@@ -113,7 +114,9 @@ do_test (void)
free (p);
TEST_VERIFY (count > 0);
- /* Large bins test. */
+ /* Large bins test. This verifies that the over-allocated parts
+ that memalign releases for future allocations can be reused by
+ memalign itself at least in some cases. */
for (i = 0; i < LN; ++ i)
{