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Reenable John Dyson's low-memory VM_WAIT code for page reactivations out

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of PQ_CACHE.  Add comments explaining what it accomplishes and its
    limitations.
This commit is contained in:
Matthew Dillon 1999-01-23 06:00:27 +00:00
parent b8808468dd
commit 7615edaa49
Notes: svn2git 2020-12-20 02:59:44 +00:00 
svn path=/head/; revision=43086
1 changed files with 13 additions and 7 deletions
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20
sys/vm/vm_fault.c
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@ -66,7 +66,7 @@
* any improvements or extensions that they make and grant Carnegie the
* rights to redistribute these changes.
*
* $Id: vm_fault.c,v 1.94 1999/01/21 08:29:10 dillon Exp $
* $Id: vm_fault.c,v 1.95 1999/01/21 09:35:38 dillon Exp $
*/
/*
@ -309,12 +309,18 @@ RetryFault:;
vm_page_unqueue_nowakeup(fs.m);
splx(s);
#if 0
/*
* Code removed. In a low-memory situation (say, a
* memory-bound program is running), the last thing you
* do is starve reactivations for other processes.
* XXX we need to find a better way.
* This code is designed to prevent thrashing in a
* low-memory situation by assuming that pages placed
* in the cache are generally inactive, so if a cached
* page is requested and we are low on memory, we try
* to wait for the low-memory condition to be resolved.
*
* This code cannot handle a major memory starvation
* situation where pages are forced into the cache and
* may cause 'good' programs to stall. As of 22Jan99
* the problem is still under discussion and not
* resolved.
*/
if (((queue - fs.m->pc) == PQ_CACHE) &&
(cnt.v_free_count + cnt.v_cache_count) < cnt.v_free_min) {
@ -323,7 +329,7 @@ RetryFault:;
VM_WAIT;
goto RetryFault;
}
#endif
/*
* Mark page busy for other processes, and the
* pagedaemon. If it still isn't completely valid