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    SubjectRe: [PATCH] Prevent OOM from killing init
    >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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