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Improve vmem tuning for platforms without a direct map.

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On platforms without a direct map (i.e., platforms without
UMA_MD_SMALL_ALLOC defined), the boundary tag allocator reserves a
number of tags for use when allocating a new slab of boundary tags,
as such platforms require free boundary tags in order to allocate
boundary tags.  r327899 increased the number of boundary tags required
for a KVA allocation in the worst case, and the aforementioned
reservation was not updated accordingly.  In some cases, this could
lead to a system hang.  Fix the problem by increasing this reservation.

Also reduce KVA_QUANTUM on systems lacking superpage support.
The previous import quantum (4MB with a 4KB page size) was quite large
for systems with limited KVA, and fragmentation in kernel_arena could
cause kernel memory allocation failures even with a substantial amount
of free KVA.

Reported and tested by:	jhibbits
Reviewed by:	alc, kib
No objections:	jeff
MFC after:	2 weeks
Sponsored by:	The FreeBSD Foundation
Differential Revision:	https://reviews.freebsd.org/D19337
This commit is contained in:
Mark Johnston 2019-02-25 19:22:13 +00:00
parent f42230d856
commit 2b6010705c
2 changed files with 6 additions and 4 deletions
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6
sys/kern/subr_vmem.c
View File

@ -689,9 +689,11 @@ vmem_startup(void)
/*
* Reserve enough tags to allocate new tags. We allow multiple
* CPUs to attempt to allocate new tags concurrently to limit
* false restarts in UMA.
* false restarts in UMA. vmem_bt_alloc() allocates from a per-domain
* arena, which may involve importing a range from the kernel arena,
* so we need to keep at least 2 * BT_MAXALLOC tags reserved.
*/
uma_zone_reserve(vmem_bt_zone, BT_MAXALLOC * (mp_ncpus + 1) / 2);
uma_zone_reserve(vmem_bt_zone, 2 * BT_MAXALLOC * mp_ncpus);
uma_zone_set_allocf(vmem_bt_zone, vmem_bt_alloc);
#endif
}

4
sys/vm/vm_kern.c
View File

@ -124,8 +124,8 @@ SYSCTL_ULONG(_vm, OID_AUTO, max_kernel_address, CTLFLAG_RD,
#if VM_NRESERVLEVEL > 0
#define KVA_QUANTUM_SHIFT (VM_LEVEL_0_ORDER + PAGE_SHIFT)
#else
/* On non-superpage architectures want large import sizes. */
#define KVA_QUANTUM_SHIFT (10 + PAGE_SHIFT)
/* On non-superpage architectures we want large import sizes. */
#define KVA_QUANTUM_SHIFT (8 + PAGE_SHIFT)
#endif
#define KVA_QUANTUM (1 << KVA_QUANTUM_SHIFT)