svn commit: r364819 - head/sys/kern
Mark Johnston
markj at FreeBSD.org
Wed Aug 26 14:31:36 UTC 2020
Author: markj
Date: Wed Aug 26 14:31:35 2020
New Revision: 364819
URL: https://svnweb.freebsd.org/changeset/base/364819
Log:
vmem: Avoid allocating span tags when segments are never released.
vmem uses span tags to delimit imported segments, so that they can be
released if the segment becomes free in the future. However, the
per-domain kernel KVA arenas never release resources, so the span tags
between imported ranges are unused when the ranges are contiguous.
Furthermore, such span tags prevent coalescing of free segments across
KVA_QUANTUM boundaries, resulting in internal fragmentation which
inhibits superpage promotion in the kernel map.
Stop allocating span tags in arenas that never release resources. This
saves a small amount of memory and allows free segements to coalesce
across import boundaries. This manifests as improved kernel superpage
usage during poudriere runs, which also helps to reduce physical memory
fragmentation by reducing the number of broken partially populated
reservations.
Tested by: pho
Sponsored by: The FreeBSD Foundation
Differential Revision: https://reviews.freebsd.org/D24548
Modified:
head/sys/kern/subr_vmem.c
Modified: head/sys/kern/subr_vmem.c
==============================================================================
--- head/sys/kern/subr_vmem.c Wed Aug 26 14:02:38 2020 (r364818)
+++ head/sys/kern/subr_vmem.c Wed Aug 26 14:31:35 2020 (r364819)
@@ -249,6 +249,18 @@ static struct vmem memguard_arena_storage;
vmem_t *memguard_arena = &memguard_arena_storage;
#endif
+static bool
+bt_isbusy(bt_t *bt)
+{
+ return (bt->bt_type == BT_TYPE_BUSY);
+}
+
+static bool
+bt_isfree(bt_t *bt)
+{
+ return (bt->bt_type == BT_TYPE_FREE);
+}
+
/*
* Fill the vmem's boundary tag cache. We guarantee that boundary tag
* allocation will not fail once bt_fill() passes. To do so we cache
@@ -795,25 +807,49 @@ SYSINIT(vfs, SI_SUB_CONFIGURE, SI_ORDER_ANY, vmem_star
static void
vmem_add1(vmem_t *vm, vmem_addr_t addr, vmem_size_t size, int type)
{
- bt_t *btspan;
- bt_t *btfree;
+ bt_t *btfree, *btprev, *btspan;
+ VMEM_ASSERT_LOCKED(vm);
MPASS(type == BT_TYPE_SPAN || type == BT_TYPE_SPAN_STATIC);
MPASS((size & vm->vm_quantum_mask) == 0);
- btspan = bt_alloc(vm);
- btspan->bt_type = type;
- btspan->bt_start = addr;
- btspan->bt_size = size;
- bt_insseg_tail(vm, btspan);
+ if (vm->vm_releasefn == NULL) {
+ /*
+ * The new segment will never be released, so see if it is
+ * contiguous with respect to an existing segment. In this case
+ * a span tag is not needed, and it may be possible now or in
+ * the future to coalesce the new segment with an existing free
+ * segment.
+ */
+ btprev = TAILQ_LAST(&vm->vm_seglist, vmem_seglist);
+ if ((!bt_isbusy(btprev) && !bt_isfree(btprev)) ||
+ btprev->bt_start + btprev->bt_size != addr)
+ btprev = NULL;
+ } else {
+ btprev = NULL;
+ }
- btfree = bt_alloc(vm);
- btfree->bt_type = BT_TYPE_FREE;
- btfree->bt_start = addr;
- btfree->bt_size = size;
- bt_insseg(vm, btfree, btspan);
- bt_insfree(vm, btfree);
+ if (btprev == NULL || bt_isbusy(btprev)) {
+ if (btprev == NULL) {
+ btspan = bt_alloc(vm);
+ btspan->bt_type = type;
+ btspan->bt_start = addr;
+ btspan->bt_size = size;
+ bt_insseg_tail(vm, btspan);
+ }
+ btfree = bt_alloc(vm);
+ btfree->bt_type = BT_TYPE_FREE;
+ btfree->bt_start = addr;
+ btfree->bt_size = size;
+ bt_insseg_tail(vm, btfree);
+ bt_insfree(vm, btfree);
+ } else {
+ bt_remfree(vm, btprev);
+ btprev->bt_size += size;
+ bt_insfree(vm, btprev);
+ }
+
vm->vm_size += size;
}
@@ -1147,6 +1183,7 @@ vmem_set_import(vmem_t *vm, vmem_import_t *importfn,
{
VMEM_LOCK(vm);
+ KASSERT(vm->vm_size == 0, ("%s: arena is non-empty", __func__));
vm->vm_importfn = importfn;
vm->vm_releasefn = releasefn;
vm->vm_arg = arg;
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