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List:       linux-mm
Subject:    Re: Kernel 2.6.8.1: swap storm of death - nr_requests > 1024 on swap partition
From:       Marcelo Tosatti <marcelo.tosatti () cyclades ! com>
Date:       2004-08-30 17:16:04
Message-ID: 20040830171604.GA2103 () logos ! cnet
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Karl, 

Please apply the attached patch and rerun your tests. With it applied, 
the OOM killer output will print the number of available swap pages at
the time of killing.

In the meantime I'll be doing some more tests.

On Mon, Aug 30, 2004 at 08:01:19PM +0200, Karl Vogel wrote:
> Marcelo Tosatti wrote:
> 
> >What is the problem Karl is seeing again? There seem to be several, lets
> >separate them
> >
> >- OOM killer triggering (if there's swap space available and 
> >"enough" anonymous memory to be swapped out this should not happen). 
> >One of his complaint on the initial report (about the OOM killer).
> 
> Correct. On my 512Mb RAM system with 1Gb swap partition, running a 
> calloc(1Gb) causes the process to get OOM killed when using CFQ.
> The problem is not CFQ as such.. the problem is when nr_requests is too 
> large (8192 being the default for CFQ).
> 
> The same will happen with the default nr_request of 128 which AS uses, 
> if you use a low memory system. e.g. I booted with mem=128M and then a 
> calloc(128Mb) can trigger the OOM.
> 
> >- Swap cache not freed after test app exists. Should not be a
> >problem because such memory will be freed as soon as theres 
> >pressure, I think.
> 
> After the OOM killer killed the calloc() task, the SwapCache still 
> contains a large chunk of the original allocation. This get's cleared if 
> there is alot of I/O (example: dd if=/dev/hdX of=/dev/null).
> 
> However, without the I/O's it doesn't seem to get freed.. this also 
> causes a second run of calloc(1Gb) to fail as the SwapCache still 
> accounts for used memory.
> 
> >How can you reproduce that?
> 
> It should be reproducable as follows:
> - boot with mem=512M
> - have a 1Gb swap partition / swapfile (the size doesn't really matter)
> - use CFQ or set nr_requests to 8192 on the drive _hosting the swap_
> - run  'expunge 1024'   (might work the 1st time, if so, run it again)
> 
> 
> --- expunge.c program source ---
> #include <stdio.h>
> #include <stdlib.h>
> 
> int main(int argc, char *argv[])
> {
>     char *p= calloc(1, atol(argv[1])*1024L*1024L);
>     if (!p) {
>         perror("calloc");
>         exit(1);
>     }
>     return 0;
> }
> --- expunge.c program source ---
> 
> 
> 
> Another thing that you can try:
> - boot with mem=128M
> - have enough swap
> - execute:  while true; do expunge 128; done
> 
> This will trigger an OOM even with AS (nr_requests = 128)
> 
> 
> 
> After the OOM, SwapCache still holds part of the allocation.

["vm-reclaim2.patch" (text/plain)]

--- mm/page_alloc.c.orig	2004-08-24 20:37:53.000000000 -0300
+++ mm/page_alloc.c	2004-08-24 22:51:49.498375608 -0300
@@ -1021,11 +1021,12 @@
 void show_free_areas(void)
 {
 	struct page_state ps;
-	int cpu, temperature;
+	int cpu, temperature, i;
 	unsigned long active;
 	unsigned long inactive;
 	unsigned long free;
 	struct zone *zone;
+	unsigned int swap_pages = 0;
 
 	for_each_zone(zone) {
 		show_node(zone);
@@ -1086,6 +1087,8 @@
 			" active:%lukB"
 			" inactive:%lukB"
 			" present:%lukB"
+			" pages_scanned:%lu"
+			" all_unreclaimable? %s"
 			"\n",
 			zone->name,
 			K(zone->free_pages),
@@ -1094,7 +1097,9 @@
 			K(zone->pages_high),
 			K(zone->nr_active),
 			K(zone->nr_inactive),
-			K(zone->present_pages)
+			K(zone->present_pages),
+			zone->pages_scanned,
+			(zone->all_unreclaimable ? "yes" : "no")
 			);
 		printk("protections[]:");
 		for (i = 0; i < MAX_NR_ZONES; i++)
@@ -1125,6 +1130,18 @@
 		printk("= %lukB\n", K(total));
 	}
 
+	swap_list_lock();
+	for (i = 0; i < nr_swapfiles; i++) {
+		if (!(swap_info[i].flags & SWP_USED) ||
+		     (swap_info[i].flags & SWP_WRITEOK))
+                       continue;
+		swap_pages += swap_info[i].inuse_pages;
+	}
+	swap_pages += nr_swap_pages;
+	swap_list_unlock();
+
+	printk("nr_free_swap_pages: %u\n", swap_pages);
+
 	show_swap_cache_info();
 }
 

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