DragonFlyBSD

--- vm_zeroidle.c.orig 2010-05-26 15:09:26 -0700
+++ vm_zeroidle.c 2010-05-26 15:12:50 -0700
@ -90,6 +90,9 @
STATE_RELEASE_PAGE
};

#define DEFAULT_SLEEP_TIME (hz / 10)
#define LONG_SLEEP_TIME (hz * 10)
+
static int zero_state;

/*
@ -112,6 +115,20 @
        return (1);
 }

/*
* vm_pagezero should sleep for a long time when idlezero is disabled or when
+ * there is an excess of zeroed pages.
+ */
static int
+vm_page_zero_time(void)
{
+ if (idlezero_enable == 0)
+ return (LONG_SLEEP_TIME);
+ if (vm_page_zero_count >= ZIDLE_HI(vmstats.v_free_count))
+ return (LONG_SLEEP_TIME);
+ return (DEFAULT_SLEEP_TIME);
}

static void
vm_pagezero(void __unused *arg) {
@ -120,6 +137,7 @
enum zeroidle_state state = STATE_IDLE;
char *pg = NULL;
int npages = 0;
+ int sleep_time;
int i = 0;

/*
@ -132,6 +150,7 @
        rel_mplock();
        lwkt_setpri_self(TDPRI_IDLE_WORK);
        lwkt_setcpu_self(globaldata_find(ncpus - 1));
+       sleep_time = DEFAULT_SLEEP_TIME;

/*
 * Loop forever
@ -142,9 +161,10 @
                        /*
                 * Wait for work.
                         /
-                       tsleep(&zero_state, 0, "pgzero", hz / 10);
+                       tsleep(&zero_state, 0, "pgzero", sleep_time);
                        if (vm_page_zero_check())
                                npages = idlezero_rate / 10;
+                       sleep_time = vm_page_zero_time();
                        if (npages)
                                state = STATE_GET_PAGE; / Fallthrough */
                        break;
@ -198,7 +218,8 @
                        }
                        break;
                }
-               lwkt_switch();
+               if (lwkt_check_resched(curthread))
+                       lwkt_switch();
        }
 }

=================================

The patch above should cause vm_zeroidle to sleep for longer periods of time (hz

• 10) when it is disabled or when there are a lot of pages. Longer sleep times
  would be better when there're no pages to zero.

It also conditionalizes the lwkt_switch(); I think this is worth doing, since
lwkt_check_resched() is cheaper than lwkt_switch(). This may or may not be worth
doing.

-- vs