Limit number of simultanious asynchronous swap pager I/Os that can
be in progress at any given moment.
Add two swap tuneables to sysctl:
vm.swap_async_max: 4
vm.swap_cluster_max: 16
Recommended values are a cluster size of 8 or 16 pages. async_max is
about right for 1-4 swap devices. Reduce to 2 if swap is eating too much
bandwidth, or even 1 if swap is both eating too much bandwidth and sitting
on a slow network (10BaseT).
The defaults work well across a broad range of configurations and should
normally be left alone.
This commit is contained in:
dillon
parent
1e914ccb42
commit
6203c54a6d
@ -64,7 +64,7 @@
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*
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* @(#)swap_pager.c 8.9 (Berkeley) 3/21/94
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*
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* $Id: swap_pager.c,v 1.112 1999/01/27 18:19:52 dillon Exp $
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* $Id: swap_pager.c,v 1.113 1999/02/06 07:22:21 dillon Exp $
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*/
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#include <sys/param.h>
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@ -75,6 +75,7 @@
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#include <sys/vnode.h>
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#include <sys/malloc.h>
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#include <sys/vmmeter.h>
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#include <sys/sysctl.h>
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#include <sys/blist.h>
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#include <sys/lock.h>
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@ -107,15 +108,33 @@ extern int vm_swap_size; /* number of free swap blocks, in pages */
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int swap_pager_full; /* swap space exhaustion (w/ hysteresis)*/
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static int nsw_rcount; /* free read buffers */
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static int nsw_wcount; /* free write buffers */
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static int nsw_hysteresis; /* hysteresis */
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static int max_pageout_cluster; /* maximum VOP I/O allowed */
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static int nsw_wcount_sync; /* limit write buffers / synchronous */
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static int nsw_wcount_async; /* limit write buffers / asynchronous */
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static int nsw_wcount_async_max;/* assigned maximum */
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static int nsw_cluster_max; /* maximum VOP I/O allowed */
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static int sw_alloc_interlock; /* swap pager allocation interlock */
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struct blist *swapblist;
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static struct swblock **swhash;
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static int swhash_mask;
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static int swap_async_max = 4; /* maximum in-progress async I/O's */
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static int swap_cluster_max; /* maximum VOP I/O allowed */
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#ifndef DISALLOW_SWAP_TUNE
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SYSCTL_INT(_vm, OID_AUTO, swap_async_max,
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CTLFLAG_RW, &swap_async_max, 0, "Maximum running async swap ops");
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SYSCTL_INT(_vm, OID_AUTO, swap_cluster_max,
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CTLFLAG_RW, &swap_cluster_max, 0, "Maximum swap I/O cluster (pages)");
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#else
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SYSCTL_INT(_vm, OID_AUTO, swap_async_max,
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CTLFLAG_RD, &swap_async_max, 0, "");
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SYSCTL_INT(_vm, OID_AUTO, swap_cluster_max,
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CTLFLAG_RD, &swap_cluster_max, 0, "");
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#endif
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/*
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* "named" and "unnamed" anon region objects. Try to reduce the overhead
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@ -258,16 +277,30 @@ swap_pager_swap_init()
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* initialize workable values (0 will work for hysteresis
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* but it isn't very efficient).
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*
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* The max_pageout_cluster is constrained by the bp->b_pages[]
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* The nsw_cluster_max is constrained by the bp->b_pages[]
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* array (MAXPHYS/PAGE_SIZE) and our locally defined
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* MAX_PAGEOUT_CLUSTER. Also be aware that swap ops are
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* constrained by the swap device interleave stripe size.
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*
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* Currently we hardwire nsw_wcount_async to 4. This limit is
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* designed to prevent other I/O from having high latencies due to
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* our pageout I/O. The value 4 works well for one or two active swap
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* devices but is probably a little low if you have more. Even so,
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* a higher value would probably generate only a limited improvement
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* with three or four active swap devices since the system does not
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* typically have to pageout at extreme bandwidths. We will want
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* at least 2 per swap devices, and 4 is a pretty good value if you
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* have one NFS swap device due to the command/ack latency over NFS.
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* So it all works out pretty well.
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*/
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swap_cluster_max = min((MAXPHYS/PAGE_SIZE), MAX_PAGEOUT_CLUSTER);
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nsw_rcount = (nswbuf + 1) / 2;
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nsw_wcount = (nswbuf + 3) / 4;
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nsw_hysteresis = nsw_wcount / 2;
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max_pageout_cluster = min((MAXPHYS/PAGE_SIZE), MAX_PAGEOUT_CLUSTER);
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nsw_wcount_sync = (nswbuf + 3) / 4;
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nsw_wcount_async = 4;
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nsw_wcount_async_max = nsw_wcount_async;
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nsw_cluster_max = swap_cluster_max;
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/*
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* Initialize our zone. Right now I'm just guessing on the number
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@ -1015,6 +1048,57 @@ swap_pager_putpages(object, m, count, sync, rtvals)
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/*
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* Step 2
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*
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* Update nsw parameters from swap_async_max and swap_cluster_max
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* sysctl values. Do not let the sysop crash the machine with bogus
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* numbers.
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*/
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#ifndef DISALLOW_SWAP_TUNE
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if (swap_async_max != nsw_wcount_async_max) {
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int n;
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int s;
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/*
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* limit range
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*/
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if ((n = swap_async_max) > nswbuf / 2)
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n = nswbuf / 2;
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if (n < 1)
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n = 1;
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swap_async_max = n;
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/*
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* Adjust difference ( if possible ). If the current async
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* count is too low, we may not be able to make the adjustment
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* at this time.
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*/
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s = splvm();
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n -= nsw_wcount_async_max;
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if (nsw_wcount_async + n >= 0) {
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nsw_wcount_async += n;
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nsw_wcount_async_max += n;
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wakeup(&nsw_wcount_async);
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}
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splx(s);
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}
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if (swap_cluster_max != nsw_cluster_max) {
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int n;
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if ((n = swap_cluster_max) < 1)
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n = 1;
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if (n > min((MAXPHYS/PAGE_SIZE), MAX_PAGEOUT_CLUSTER))
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n = min((MAXPHYS/PAGE_SIZE), MAX_PAGEOUT_CLUSTER);
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swap_cluster_max = n;
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nsw_cluster_max = n;
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}
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#endif
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/*
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* Step 3
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*
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* Assign swap blocks and issue I/O. We reallocate swap on the fly.
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* The page is left dirty until the pageout operation completes
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* successfully.
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@ -1031,7 +1115,7 @@ swap_pager_putpages(object, m, count, sync, rtvals)
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*/
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n = min(BLIST_MAX_ALLOC, count - i);
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n = min(n, max_pageout_cluster);
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n = min(n, nsw_cluster_max);
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/*
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* Get biggest block of swap we can. If we fail, fall
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@ -1072,12 +1156,17 @@ swap_pager_putpages(object, m, count, sync, rtvals)
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* NOTE: B_PAGING is set by pbgetvp()
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*/
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bp = getpbuf(&nsw_wcount);
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if (sync == TRUE) {
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bp = getpbuf(&nsw_wcount_sync);
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bp->b_flags = B_BUSY;
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} else {
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bp = getpbuf(&nsw_wcount_async);
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bp->b_flags = B_BUSY | B_ASYNC;
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}
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bp->b_spc = NULL; /* not used, but NULL-out anyway */
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pmap_qenter((vm_offset_t)bp->b_data, &m[i], n);
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bp->b_flags = B_BUSY | B_ASYNC;
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bp->b_proc = &proc0; /* XXX (but without B_PHYS this is ok) */
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bp->b_rcred = bp->b_wcred = bp->b_proc->p_ucred;
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@ -1396,8 +1485,15 @@ swp_pager_async_iodone(bp)
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* release the physical I/O buffer
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*/
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relpbuf(bp, ((bp->b_flags & B_READ) ? &nsw_rcount : &nsw_wcount));
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relpbuf(
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bp,
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((bp->b_flags & B_READ) ? &nsw_rcount :
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((bp->b_flags & B_ASYNC) ?
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&nsw_wcount_async :
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&nsw_wcount_sync
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)
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)
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);
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splx(s);
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}
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