Messages in this thread Patch in this message | | | Date | Sat, 24 Mar 2001 20:59:10 +0000 | From | Jonathan Morton <> | Subject | Re: [PATCH] Prevent OOM from killing init |
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>Right now my best approximation is to make the OOM test be as optimistic as >it is safe to be, and the vm_enough_memory() test as pessimistic as >sensible. Expect a test patch to appear on this list soon.
...and here it is!
This fixes a number of small but linked problems:
- malloc() never returned 0 when the system ran out of memory, instead the OOM killer was triggered. Now, malloc() will return 0 if the calling process is more than 4 times the size of the amount of free memory. As a speedup, available swap space is not considered unless physical memory is not sufficient to contain the process. Note that if overcommit_memory is switched on, malloc() will never return 0 anyway.
- OOM killer was triggered too early - now takes account of buffer and cache memory, which can be cannibalised before the system has completely run out.
- OOM killer badness() factors readjusted in favour of Oracle-like processes (consuming 10's of MB of RAM but up for 3 days or so and with a low-order UID? Now less likely to be killed...)
--- begin oom-patch.diff --- diff -u linux-2.4.1.orig/mm/mmap.c linux/mm/mmap.c --- linux-2.4.1.orig/mm/mmap.c Mon Jan 29 16:10:41 2001 +++ linux/mm/mmap.c Sat Mar 24 19:29:51 2001 @@ -54,6 +54,7 @@ */
long free; + struct sysinfo swp_info;
/* Sometimes we want to use more memory than we have. */ if (sysctl_overcommit_memory) @@ -62,8 +63,32 @@ free = atomic_read(&buffermem_pages); free += atomic_read(&page_cache_size); free += nr_free_pages(); - free += nr_swap_pages; - return free > pages; + + /* Attempt to curtail memory allocations before hard OOM occurs. + * Based on current process size, which is hopefully a good and fast heuristic. + * Also fix bug where the real OOM limit of (free == freepages.min) is not taken into account. + * In fact, we use freepages.high as the threshold to make sure there's still room for buffers+cache. + * + * -- Jonathan "Chromatix" Morton, 24th March 2001 + */ + + if(current && current->mm) + free -= (current->mm->total_vm / 4); + + free -= freepages.high; + + /* Since getting swap info is expensive, see if our allocation can happen in physical RAM */ + if(free > pages) + return 1; + + /* Use the number of FREE swap pages, not the total */ + si_swapinfo(&swp_info); + free += swp_info.freeswap; + + if(free > pages) + return 1; + + return 0; }
/* Remove one vm structure from the inode's i_mapping address space. */ Only in linux/mm/: mmap.c~ diff -u linux-2.4.1.orig/mm/oom_kill.c linux/mm/oom_kill.c --- linux-2.4.1.orig/mm/oom_kill.c Tue Nov 14 18:56:46 2000 +++ linux/mm/oom_kill.c Sat Mar 24 20:35:20 2001 @@ -76,7 +76,9 @@ run_time = (jiffies - p->start_time) >> (SHIFT_HZ + 10);
points /= int_sqrt(cpu_time); - points /= int_sqrt(int_sqrt(run_time)); + + /* Long-running processes are *very* important, so don't take the 4th root */ + points /= run_time;
/* * Niced processes are most likely less important, so double @@ -93,6 +95,10 @@ p->uid == 0 || p->euid == 0) points /= 4;
+ /* Much the same goes for processes with low UIDs */ + if(p->uid < 100 || p->euid < 100) + points /= 2; + /* * We don't want to kill a process with direct hardware access. * Not only could that mess up the hardware, but usually users @@ -192,12 +198,20 @@ int out_of_memory(void) { struct sysinfo swp_info; + long free;
/* Enough free memory? Not OOM. */ - if (nr_free_pages() > freepages.min) + free = nr_free_pages(); + if (free > freepages.min) + return 0; + + if (free + nr_inactive_clean_pages() > freepages.low) return 0;
- if (nr_free_pages() + nr_inactive_clean_pages() > freepages.low) + /* Buffers and caches can be freed up (Jonathan "Chromatix" Morton) */ + free += atomic_read(&buffermem_pages); + free += atomic_read(&page_cache_size); + if (free > freepages.low) return 0;
/* Enough swap space left? Not OOM. */ Only in linux/mm/: oom_kill.c~ --- end oom-patch.diff --- -------------------------------------------------------------- from: Jonathan "Chromatix" Morton mail: chromi@cyberspace.org (not for attachments) big-mail: chromatix@penguinpowered.com uni-mail: j.d.morton@lancaster.ac.uk The key to knowledge is not to rely on people to teach you it.
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