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Handle a special case when a slab can fit only one allocation,

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and zone has a large alignment. With alignment taken into
account uk_rsize will be greater than space in a slab. However,
since we have only one item per slab, it is always naturally
aligned.

Code that will panic before this change with 4k page:

	z = uma_zcreate("test", 3984, NULL, NULL, NULL, NULL, 31, 0);
	uma_zalloc(z, M_WAITOK);

A practical scenario to hit the panic is a machine with 56 CPUs
and 2 NUMA domains, which yields in zone size of 3984.

PR:		227116
MFC after:	2 weeks
This commit is contained in:
Gleb Smirnoff 2018-04-02 05:11:59 +00:00
parent d8120b3687
commit 1ca6ed4589
1 changed files with 9 additions and 1 deletions
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10
sys/vm/uma_core.c
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@ -1290,7 +1290,15 @@ keg_small_init(uma_keg_t keg)
else
shsize = sizeof(struct uma_slab);
keg->uk_ipers = (slabsize - shsize) / rsize;
if (rsize <= slabsize - shsize)
keg->uk_ipers = (slabsize - shsize) / rsize;
else {
/* Handle special case when we have 1 item per slab, so
* alignment requirement can be relaxed. */
KASSERT(keg->uk_size <= slabsize - shsize,
("%s: size %u greater than slab", __func__, keg->uk_size));
keg->uk_ipers = 1;
}
KASSERT(keg->uk_ipers > 0 && keg->uk_ipers <= SLAB_SETSIZE,
("%s: keg->uk_ipers %u", __func__, keg->uk_ipers));