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Prevent arc_c collapse 

Adjusting arc_c directly is racy because it can happen in the context
of multiple threads.  It should always be >= 2 * maxblocksize.  Set it
to a known valid value rather than adjusting it directly.

In addition refactor arc_shrink() to a simpler structure, protect against
underflow in the calculation of the new arc_c value.

Signed-off-by: Tim Chase <tim@chase2k.com>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reverts: 935434ef
Closes: 
Closes:
This commit is contained in:
Tim Chase 2016-01-22 07:37:37 -06:00 committed by Brian Behlendorf
parent a08add3067
commit 6f7acfc9c9
1 changed files with 9 additions and 8 deletions
module/zfs
arc.c

17
module/zfs/arc.c
View File

@ -3179,13 +3179,10 @@ arc_flush(spa_t *spa, boolean_t retry)
void void
arc_shrink(int64_t to_free) arc_shrink(int64_t to_free)
{ {
if (arc_c > arc_c_min) { uint64_t c = arc_c;
if (arc_c > arc_c_min + to_free)
atomic_add_64(&arc_c, -to_free);
else
arc_c = arc_c_min;
if (c > to_free && c - to_free > arc_c_min) {
arc_c = c - to_free;
atomic_add_64(&arc_p, -(arc_p >> arc_shrink_shift)); atomic_add_64(&arc_p, -(arc_p >> arc_shrink_shift));
if (arc_c > arc_size) if (arc_c > arc_size)
arc_c = MAX(arc_size, arc_c_min); arc_c = MAX(arc_size, arc_c_min);
@ -3193,6 +3190,8 @@ arc_shrink(int64_t to_free)
arc_p = (arc_c >> 1); arc_p = (arc_c >> 1);
ASSERT(arc_c >= arc_c_min); ASSERT(arc_c >= arc_c_min);
ASSERT((int64_t)arc_p >= 0); ASSERT((int64_t)arc_p >= 0);
} else {
arc_c = arc_c_min;
} }
if (arc_size > arc_c) if (arc_size > arc_c)
@ -3762,7 +3761,7 @@ arc_adapt(int bytes, arc_state_t *state)
* If we're within (2 * maxblocksize) bytes of the target * If we're within (2 * maxblocksize) bytes of the target
* cache size, increment the target cache size * cache size, increment the target cache size
*/ */
VERIFY3U(arc_c, >=, 2ULL << SPA_MAXBLOCKSHIFT); ASSERT3U(arc_c, >=, 2ULL << SPA_MAXBLOCKSHIFT);
if (arc_size >= arc_c - (2ULL << SPA_MAXBLOCKSHIFT)) { if (arc_size >= arc_c - (2ULL << SPA_MAXBLOCKSHIFT)) {
atomic_add_64(&arc_c, (int64_t)bytes); atomic_add_64(&arc_c, (int64_t)bytes);
if (arc_c > arc_c_max) if (arc_c > arc_c_max)
@ -5105,7 +5104,9 @@ arc_tempreserve_space(uint64_t reserve, uint64_t txg)
int error; int error;
uint64_t anon_size; uint64_t anon_size;
if (reserve > arc_c/4 && !arc_no_grow) if (!arc_no_grow &&
reserve > arc_c/4 &&
reserve * 4 > (2ULL << SPA_MAXBLOCKSHIFT))
arc_c = MIN(arc_c_max, reserve * 4); arc_c = MIN(arc_c_max, reserve * 4);
/* /*