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Subject[PATCH] 2.2.1{3,4,5} VM fix
Hi Alan,

here's the patch for the 2.2.15* out of memory problem.
This patch does a number of things:
- make kswapd sleep just HZ, just like in 2.3
- don't start freeing memory from a user process when
we're at or just below the limit:
- we need the kernel lock so freeing memory
together with kswapd isn't possible anyway
- if kswapd can keep up, there's no latency
penalty for (kernel) memory allocations
- when we truly are low on memory or kswapd
can't keep up, then any __GFP_WAIT allocations
_will_ wait while trying to free memory
(so there's less chance of running out for
GFP_ATOMIC ones)
- wake up kswapd somewhat earlier (instead of too late)

This should be enough to make sure that 2.2.1* doesn't
run out of memory on a slight network flooding any more.
Note that I have only compiled the code with this patch
and not tried it, this wouldn't have worked anyway because
I can't create the problem situation (fast network, etc)
at home...

regards,

Rik
--
The Internet is not a network of computers. It is a network
of people. That is its real strength.



--- linux-2.2.15-pre3/mm/vmscan.c.orig Wed Jan 19 21:18:54 2000
+++ linux-2.2.15-pre3/mm/vmscan.c Wed Jan 19 22:06:34 2000
@@ -490,12 +490,13 @@
{
if (do_try_to_free_pages(GFP_KSWAPD))
{
+ run_task_queue(&tq_disk);
if (tsk->need_resched)
schedule();
continue;
}
tsk->state = TASK_INTERRUPTIBLE;
- schedule_timeout(10*HZ);
+ schedule_timeout(HZ);
}
}
}
@@ -509,18 +510,16 @@
* from user processes, because the locking issues are
* nasty to the extreme (file write locks, and MM locking)
*
- * One option might be to let kswapd do all the page-out
- * and VM page table scanning that needs locking, and this
- * process thread could do just the mmap shrink stage that
- * can be done by just dropping cached pages without having
- * any deadlock issues.
+ * If we're on or just slighly below freepages.low, kswapd
+ * should manage on its own, we just give it a nudge. This
+ * should also reduce contention for the kernel lock above.
*/
int try_to_free_pages(unsigned int gfp_mask)
{
int retval = 1;

wake_up_interruptible(&kswapd_wait);
- if (gfp_mask & __GFP_WAIT)
+ if ((gfp_mask & __GFP_WAIT) && (nr_free_pages < (freepages.low - 4)))
retval = do_try_to_free_pages(gfp_mask);
return retval;
}
--- linux-2.2.15-pre3/mm/page_alloc.c.orig Wed Jan 19 21:32:05 2000
+++ linux-2.2.15-pre3/mm/page_alloc.c Wed Jan 19 21:42:00 2000
@@ -212,7 +212,7 @@
if (!(current->flags & PF_MEMALLOC)) {
int freed;

- if (nr_free_pages > freepages.min) {
+ if (nr_free_pages > freepages.low) {
if (!low_on_memory)
goto ok_to_allocate;
if (nr_free_pages >= freepages.high) {

-
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