• David Rientjes's avatar
    oom: move oom_adj value from task_struct to mm_struct · 2ff05b2b
    David Rientjes authored
    The per-task oom_adj value is a characteristic of its mm more than the
    task itself since it's not possible to oom kill any thread that shares the
    mm.  If a task were to be killed while attached to an mm that could not be
    freed because another thread were set to OOM_DISABLE, it would have
    needlessly been terminated since there is no potential for future memory
    freeing.
    
    This patch moves oomkilladj (now more appropriately named oom_adj) from
    struct task_struct to struct mm_struct.  This requires task_lock() on a
    task to check its oom_adj value to protect against exec, but it's already
    necessary to take the lock when dereferencing the mm to find the total VM
    size for the badness heuristic.
    
    This fixes a livelock if the oom killer chooses a task and another thread
    sharing the same memory has an oom_adj value of OOM_DISABLE.  This occurs
    because oom_kill_task() repeatedly returns 1 and refuses to kill the
    chosen task while select_bad_process() will repeatedly choose the same
    task during the next retry.
    
    Taking task_lock() in select_bad_process() to check for OOM_DISABLE and in
    oom_kill_task() to check for threads sharing the same memory will be
    removed in the next patch in this series where it will no longer be
    necessary.
    
    Writing to /proc/pid/oom_adj for a kthread will now return -EINVAL since
    these threads are immune from oom killing already.  They simply report an
    oom_adj value of OOM_DISABLE.
    
    Cc: Nick Piggin <npiggin@suse.de>
    Cc: Rik van Riel <riel@redhat.com>
    Cc: Mel Gorman <mel@csn.ul.ie>
    Signed-off-by: default avatarDavid Rientjes <rientjes@google.com>
    Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
    Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
    2ff05b2b
base.c 74.7 KB