Date: Tue, 8 Sep 2015 18:37:17 +0000 (UTC) From: Warner Losh <imp@FreeBSD.org> To: src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-stable@freebsd.org, svn-src-stable-10@freebsd.org Subject: svn commit: r287569 - stable/10/sys/geom Message-ID: <201509081837.t88IbHgk032284@repo.freebsd.org>
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Author: imp Date: Tue Sep 8 18:37:16 2015 New Revision: 287569 URL: https://svnweb.freebsd.org/changeset/base/287569 Log: MFC: r287405: Make out of memory behavior less pathological. Modified: stable/10/sys/geom/geom_io.c Directory Properties: stable/10/ (props changed) Modified: stable/10/sys/geom/geom_io.c ============================================================================== --- stable/10/sys/geom/geom_io.c Tue Sep 8 17:54:31 2015 (r287568) +++ stable/10/sys/geom/geom_io.c Tue Sep 8 18:37:16 2015 (r287569) @@ -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_co (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 __u } 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);
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