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MFC: r287405:

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Make out of memory behavior less pathological.
This commit is contained in:
imp 2015-09-08 18:37:16 +00:00
parent 12c2a2777a
commit bd8403067b
1 changed files with 41 additions and 7 deletions
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48
sys/geom/geom_io.c
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@ -71,7 +71,17 @@ static struct g_bioq g_bio_run_down;
static struct g_bioq g_bio_run_up;
static struct g_bioq g_bio_run_task;
static u_int pace;
/*
* Pace is a hint that we've had some trouble recently allocating
* bios, so we should back off trying to send I/O down the stack
* a bit to let the problem resolve. When pacing, we also turn
* off direct dispatch to also reduce memory pressure from I/Os
* there, at the expxense of some added latency while the memory
* pressures exist. See g_io_schedule_down() for more details
* and limitations.
*/
static volatile u_int pace;
static uma_zone_t biozone;
/*
@ -521,7 +531,8 @@ g_io_request(struct bio *bp, struct g_consumer *cp)
(pp->flags & G_PF_DIRECT_RECEIVE) != 0 &&
!g_is_geom_thread(curthread) &&
((pp->flags & G_PF_ACCEPT_UNMAPPED) != 0 ||
(bp->bio_flags & BIO_UNMAPPED) == 0 || THREAD_CAN_SLEEP());
(bp->bio_flags & BIO_UNMAPPED) == 0 || THREAD_CAN_SLEEP()) &&
pace == 0;
if (direct) {
/* Block direct execution if less then half of stack left. */
size_t st, su;
@ -688,7 +699,7 @@ g_io_deliver(struct bio *bp, int error)
bp->bio_driver2 = NULL;
bp->bio_pflags = 0;
g_io_request(bp, cp);
pace++;
pace = 1;
return;
}
@ -777,10 +788,33 @@ g_io_schedule_down(struct thread *tp __unused)
}
CTR0(KTR_GEOM, "g_down has work to do");
g_bioq_unlock(&g_bio_run_down);
if (pace > 0) {
CTR1(KTR_GEOM, "g_down pacing self (pace %d)", pace);
pause("g_down", hz/10);
pace--;
if (pace != 0) {
/*
* There has been at least one memory allocation
* failure since the last I/O completed. Pause 1ms to
* give the system a chance to free up memory. We only
* do this once because a large number of allocations
* can fail in the direct dispatch case and there's no
* relationship between the number of these failures and
* the length of the outage. If there's still an outage,
* we'll pause again and again until it's
* resolved. Older versions paused longer and once per
* allocation failure. This was OK for a single threaded
* g_down, but with direct dispatch would lead to max of
* 10 IOPs for minutes at a time when transient memory
* issues prevented allocation for a batch of requests
* from the upper layers.
*
* XXX This pacing is really lame. It needs to be solved
* by other methods. This is OK only because the worst
* case scenario is so rare. In the worst case scenario
* all memory is tied up waiting for I/O to complete
* which can never happen since we can't allocate bios
* for that I/O.
*/
CTR0(KTR_GEOM, "g_down pacing self");
pause("g_down", min(hz/1000, 1));
pace = 0;
}
CTR2(KTR_GEOM, "g_down processing bp %p provider %s", bp,
bp->bio_to->name);