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Subject[PATCH] OOM killer, version 2
Hi,

This patch introduces/fixes three things:
- out of memory killing
- a nice starting point for newbie kernel hackers
(mm/oom_kill.c is full of noteworthy notes)
- better handling of the maximum page cache & buffer
cache size

Rik.
+-------------------------------------------------------------------+
| Linux memory management tour guide. H.H.vanRiel@phys.uu.nl |
| Scouting Vries cubscout leader. http://www.phys.uu.nl/~riel/ |
+-------------------------------------------------------------------+
--- mm/Makefile.orig Sun Aug 16 17:26:38 1998
+++ mm/Makefile Sun Aug 16 17:26:57 1998
@@ -9,7 +9,7 @@

O_TARGET := mm.o
O_OBJS := memory.o mmap.o filemap.o mprotect.o mlock.o mremap.o \
- vmalloc.o slab.o \
+ vmalloc.o slab.o oom_kill.o\
swap.o vmscan.o page_io.o page_alloc.o swap_state.o swapfile.o

include $(TOPDIR)/Rules.make
--- mm/oom_kill.c.orig Tue Aug 18 19:24:07 1998
+++ mm/oom_kill.c Sat Aug 22 22:05:21 1998
@@ -1 +1,174 @@
+/*
+ * linux/mm/oom_kill.c
+ *
+ * Copyright (C) 1998 Rik van Riel
+ * Thanks go out to Claus Fischer for some serious inspiration and
+ * for goading me into coding this file...
+ *
+ * The routines in this file are used to kill a process when
+ * we're seriously out of memory. This gets called from kswapd()
+ * in linux/mm/vmscan.c when we really run out of memory.
+ *
+ * Since we won't call these routines often (on a well-configured
+ * machine) this file will double as a 'coding guide' and a signpost
+ * for newbie kernel hackers. It features several pointers to major
+ * kernel subsystems and hints as to where to find out what things do.
+ */
+#include <linux/mm.h>
+#include <linux/sched.h>
+#include <linux/stddef.h>
+#include <linux/swap.h>
+#include <linux/swapctl.h>
+#include <linux/timex.h>
+
+#define DEBUG
+/* Hmm, I remember a global declaration. Haven't found
+ * it though...
+ */
+#define min(a,b) (((a)<(b))?(a):(b))
+
+/*
+ * These definitions should move to linux/include/linux/swapctl.h
+ * but I want to change as little files as possible while the patch
+ * is still in alpha -- this will have to change before submission
+ * however -- Rik.
+ */
+typedef struct vm_kill_t
+{
+ unsigned int ram;
+ unsigned int total;
+} vm_kill_t;
+
+struct vm_kill_t vm_kill = {25, 3};
+
+/*
+ * Wow, black magic :) [read closely, the TCP code is hairier]
+ */
+inline int int_sqrt(unsigned int x)
+{
+ unsigned int out = x;
+ while (x & ~(unsigned int)1) x >>=2, out >>=1;
+ if (x) out -= out >> 2;
+ return (out ? out : 1);
+}
+
+/*
+ * Basically, points = size / (sqrt(CPU_used) * sqrt(sqrt(time_running)))
+ * with some bonusses/penalties.
+ *
+ * The definition of the task_struct, the structure describing the state
+ * of each process, can be found in include/linux/sched.h. For
+ * capability info, you should read include/linux/capability.h.
+ */
+
+inline int badness(struct task_struct *p)
+{
+ int points = p->mm->total_vm;
+ points /= int_sqrt((p->times.tms_utime + p->times.tms_stime) >> (SHIFT_HZ + 3));
+ points /= int_sqrt(int_sqrt((jiffies - p->start_time) >> (SHIFT_HZ + 10)));
+/*
+ * DEF_PRIORITY is the lenght of the standard process priority;
+ * see include/linux/sched.h for more info.
+ */
+ if (p->priority < DEF_PRIORITY)
+ points <<= 1;
+/*
+ * p->(e)uid is the process User ID, ID 0 is root, the super user. Since
+ * the super user can do anything, and does almost nothing (on a proper
+ * system), we have to assume that the process is trusted/good.
+ * Besides, the super user usually runs important system services, which
+ * we don't want to kill...
+ */
+ if (p->uid == 0 || p->euid == 0 || p->cap_effective.cap & CAP_TO_MASK(CAP_SYS_ADMIN))
+ points >>= 2;
+/*
+ * NEVER, EVER kill a process with direct hardware acces. Since
+ * they function almost as a device driver, killing one of those
+ * might hang the system -- which is something we need to prevent
+ * at all cost...
+ */
+ if (p->cap_effective.cap & CAP_TO_MASK(CAP_SYS_RAWIO)
+#ifdef __i386__
+ || p->tss.bitmap == offsetof(struct thread_struct, io_bitmap)
+#endif
+ )
+ points = 0;
+#ifdef DEBUG
+ printk(KERN_DEBUG "OOMkill: task %d (%s) got %d points\n",
+ p->pid, p->comm, points);
+#endif
+ return points;
+}
+
+inline struct task_struct * select_bad_process(void)
+{
+ int points = 0, maxpoints = 0;
+ struct task_struct *p = NULL;
+ struct task_struct *chosen = NULL;
+/*
+ * These locks are used to prevent modification of critical
+ * structures while we're working with them. Remember that
+ * Linux is a multitasking (and sometimes SMP) system.
+ * -- Luckily these nice macros are made available so we don't
+ * have to do cumbersome locking ourselves :)
+ */
+ read_lock(&tasklist_lock);
+ for_each_task(p)
+ if (p->pid)
+ points = badness(p);
+ if (points > maxpoints) {
+ chosen = p;
+ maxpoints = points;
+ }
+ read_unlock(&tasklist_lock);
+ return chosen;
+}
+
+/*
+ * The SCHED_FIFO magic should make sure that the killed context
+ * gets absolute priority when killing itself. This should prevent
+ * a looping kswapd from interfering with the process killing.
+ * Read kernel/sched.c::goodness() and kernel/sched.c::schedule()
+ * for more info.
+ */
+void oom_kill(void)
+{
+
+ struct task_struct *p = select_bad_process();
+ if (p == NULL)
+ return;
+ printk(KERN_ERR "Out of Memory: Killed process %d (%s).", p->pid, p->comm);
+ force_sig(SIGKILL, p);
+ p->policy = SCHED_FIFO;
+ p->rt_priority = 1000;
+ current->policy |= SCHED_YIELD;
+ schedule();
+ return;
+}
+
+/*
+ * Are we out of memory?
+ *
+ * We ignore swap cache pages and simplify the situation a bit.
+ * This won't do any damage, because we're only called when kswapd
+ * is already failing to free pages and when that is happening we
+ * can assume that the swap cache is very small. See the test in
+ * mm/vmscan.c::kswapd() for more info.
+ */
+
+int out_of_memory(void)
+{
+ struct sysinfo val;
+ int free_vm, kill_limit;
+ si_meminfo(&val);
+ si_swapinfo(&val);
+ kill_limit = min(vm_kill.ram * (val.totalram >> PAGE_SHIFT),
+ vm_kill.total * ((val.totalram + val.totalswap) >> PAGE_SHIFT));
+ free_vm = ((val.freeram + val.bufferram + val.freeswap) >>
+ PAGE_SHIFT) + page_cache_size - (page_cache.min_percent +
+ buffer_mem.min_percent) * num_physpages;
+ if (free_vm * 100 < kill_limit)
+ return 1;
+ return 0;
+}
--- mm/vmscan.c.orig Sat Aug 22 21:35:53 1998
+++ mm/vmscan.c Sat Aug 22 21:47:53 1998
@@ -28,6 +28,12 @@
#include <asm/bitops.h>
#include <asm/pgtable.h>

+/*
+ * OOM kill declarations. Move to .h file before submission ;)
+ */
+extern int out_of_memory(void);
+extern void oom_kill(void);
+
/*
* When are we next due for a page scan?
*/
@@ -467,7 +473,10 @@
case 0:
if (shrink_mmap(i, gfp_mask))
return 1;
- state = 1;
+ /* Don't allow a mode change when page cache or buffermem is over max */
+ if (((buffermem >> PAGE_SHIFT) * 100 < buffer_mem.max_percent * num_physpages) &&
+ (page_cache_size * 100 < page_cache.max_percent * num_physpages))
+ state = 1;
case 1:
if (shm_swap(i, gfp_mask))
return 1;
@@ -546,7 +555,7 @@
init_swap_timer();
add_wait_queue(&kswapd_wait, &wait);
while (1) {
- int tries;
+ int tries, tried, success;

current->state = TASK_INTERRUPTIBLE;
flush_signals(current);
@@ -572,18 +581,23 @@
*/
tries = pager_daemon.tries_base;
tries >>= 4*free_memory_available();
+ tried = success = 0;

do {
- do_try_to_free_page(0);
+ if (do_try_to_free_page(0))
+ success++;
+ tried++;
/*
* Syncing large chunks is faster than swapping
* synchronously (less head movement). -- Rik.
*/
if (atomic_read(&nr_async_pages) >= pager_daemon.swap_cluster)
run_task_queue(&tq_disk);
- if (free_memory_available() > 1)
+ if (free_memory_available() > 1 && tried > pager_daemon.tries_min)
break;
} while (--tries > 0);
+ if (success * 4 < tried && out_of_memory())
+ oom_kill();
}
/* As if we could ever get here - maybe we want to make this killable */
remove_wait_queue(&kswapd_wait, &wait);

-
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