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malloc: Use _int_free_chunk for remainders 

When splitting a chunk, release the tail part by calling int_free_chunk.
This avoids inserting random blocks into tcache that were never requested
by the user.  Fragmentation will be worse if they are never used again.
Note if the tail is fairly small, we could avoid splitting it at all.
Also remove an oddly placed initialization of tcache in _libc_realloc.

Reviewed-by: DJ Delorie <dj@redhat.com>
This commit is contained in:
Wilco Dijkstra 2025-03-20 16:23:07 +00:00
parent 8bac7f7a43
commit cd33535002
1 changed files with 6 additions and 9 deletions
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15
malloc/malloc.c
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@ -2646,7 +2646,7 @@ sysmalloc (INTERNAL_SIZE_T nb, mstate av)
CHUNK_HDR_SZ | PREV_INUSE);
set_foot (chunk_at_offset (old_top, old_size), CHUNK_HDR_SZ);
set_head (old_top, old_size | PREV_INUSE | NON_MAIN_ARENA);
_int_free (av, old_top, 1);
_int_free_chunk (av, old_top, chunksize (old_top), 1);
}
else
{
@ -2912,7 +2912,7 @@ sysmalloc (INTERNAL_SIZE_T nb, mstate av)
/* If possible, release the rest. */
if (old_size >= MINSIZE)
{
_int_free (av, old_top, 1);
_int_free_chunk (av, old_top, chunksize (old_top), 1);
}
}
}
@ -3530,10 +3530,7 @@ __libc_realloc (void *oldmem, size_t bytes)
if (chunk_is_mmapped (oldp))
ar_ptr = NULL;
else
{
MAYBE_INIT_TCACHE ();
ar_ptr = arena_for_chunk (oldp);
}
ar_ptr = arena_for_chunk (oldp);
/* Little security check which won't hurt performance: the allocator
never wraps around at the end of the address space. Therefore
@ -3608,7 +3605,7 @@ __libc_realloc (void *oldmem, size_t bytes)
size_t sz = memsize (oldp);
memcpy (newp, oldmem, sz);
(void) tag_region (chunk2mem (oldp), sz);
_int_free (ar_ptr, oldp, 0);
_int_free_chunk (ar_ptr, oldp, chunksize (oldp), 0);
}
}
@ -5059,7 +5056,7 @@ _int_realloc (mstate av, mchunkptr oldp, INTERNAL_SIZE_T oldsize,
(void) tag_region (oldmem, sz);
newmem = tag_new_usable (newmem);
memcpy (newmem, oldmem, sz);
_int_free (av, oldp, 1);
_int_free_chunk (av, oldp, chunksize (oldp), 1);
check_inuse_chunk (av, newp);
return newmem;
}
@ -5087,7 +5084,7 @@ _int_realloc (mstate av, mchunkptr oldp, INTERNAL_SIZE_T oldsize,
(av != &main_arena ? NON_MAIN_ARENA : 0));
/* Mark remainder as inuse so free() won't complain */
set_inuse_bit_at_offset (remainder, remainder_size);
_int_free (av, remainder, 1);
_int_free_chunk (av, remainder, chunksize (remainder), 1);
}
check_inuse_chunk (av, newp);