[src/trunk]: src/sys/uvm work around swap-space/extent performance problem wh...

[chs <chs%NetBSD.org@localhost>]

details:   https://anonhg.NetBSD.org/src/rev/26a6c8346bd2
branches:  trunk
changeset: 515211:26a6c8346bd2
user:      chs <chs%NetBSD.org@localhost>
date:      Wed Sep 19 03:41:46 2001 +0000

description:
work around swap-space/extent performance problem which causes
long pauses when processes with lots of swapped-out pages exit.

diffstat:

 sys/uvm/uvm_amap.c |  24 +++++++++++++++++++-----
 1 files changed, 19 insertions(+), 5 deletions(-)

diffs (73 lines):

diff -r 6a82c3db9032 -r 26a6c8346bd2 sys/uvm/uvm_amap.c
--- a/sys/uvm/uvm_amap.c        Wed Sep 19 03:37:58 2001 +0000
+++ b/sys/uvm/uvm_amap.c        Wed Sep 19 03:41:46 2001 +0000
@@ -1,4 +1,4 @@
-/*     $NetBSD: uvm_amap.c,v 1.34 2001/09/15 20:36:44 chs Exp $        */
+/*     $NetBSD: uvm_amap.c,v 1.35 2001/09/19 03:41:46 chs Exp $        */
 
 /*
  *
@@ -248,7 +248,7 @@
 /*
  * amap_free: free an amap
  *
- * => the amap must be locked (mainly for simplelock accounting)
+ * => the amap must be unlocked
  * => the amap should have a zero reference count and be empty
  */
 void
@@ -258,7 +258,7 @@
        UVMHIST_FUNC("amap_free"); UVMHIST_CALLED(maphist);
 
        KASSERT(amap->am_ref == 0 && amap->am_nused == 0);
-       LOCK_ASSERT(simple_lock_held(&amap->am_l));
+       LOCK_ASSERT(!simple_lock_held(&amap->am_l));
        free(amap->am_slots, M_UVMAMAP);
        free(amap->am_bckptr, M_UVMAMAP);
        free(amap->am_anon, M_UVMAMAP);
@@ -266,7 +266,6 @@
        if (amap->am_ppref && amap->am_ppref != PPREF_NONE)
                free(amap->am_ppref, M_UVMAMAP);
 #endif
-       amap_unlock(amap);      /* mainly for lock debugging */
        pool_put(&uvm_amap_pool, amap);
        UVMHIST_LOG(maphist,"<- done, freed amap = 0x%x", amap, 0, 0, 0);
 }
@@ -500,7 +499,7 @@
        UVMHIST_FUNC("amap_wipeout"); UVMHIST_CALLED(maphist);
        UVMHIST_LOG(maphist,"(amap=0x%x)", amap, 0,0,0);
 
-       LOCK_ASSERT(simple_lock_held(&amap->am_l));
+       amap_unlock(amap);
        for (lcv = 0 ; lcv < amap->am_nused ; lcv++) {
                int refs;
 
@@ -523,6 +522,20 @@
 
                        uvm_anfree(anon);
                }
+
+               /*
+                * XXX
+                * releasing the swap space held by an N anons is an O(N^2)
+                * operation because of the implementation of extents.
+                * if there are many anons, tearing down an exiting process'
+                * address space can take many seconds, which causes very
+                * annoying pauses.  we yield here to give other processes
+                * a chance to run.  this should be removed once the performance
+                * of swap space management is improved.
+                */
+
+               if (curproc->p_cpu->ci_schedstate.spc_flags & SPCF_SHOULDYIELD)
+                       preempt(NULL);
        }
 
        /*
@@ -644,6 +657,7 @@
        if (srcamap->am_ref == 1) {             /* take it over? */
                entry->etype &= ~UVM_ET_NEEDSCOPY;
                amap->am_ref--;         /* drop final reference to map */
+               amap_unlock(amap);
                amap_free(amap);        /* dispose of new (unused) amap */
                amap_unlock(srcamap);
                return;