• Uladzislau Rezki (Sony)'s avatar
    mm/vmalloc.c: add priority threshold to __purge_vmap_area_lazy() · 68571be9
    Uladzislau Rezki (Sony) authored
    Commit 763b218d ("mm: add preempt points into __purge_vmap_area_lazy()")
    introduced some preempt points, one of those is making an allocation
    more prioritized over lazy free of vmap areas.
    
    Prioritizing an allocation over freeing does not work well all the time,
    i.e.  it should be rather a compromise.
    
    1) Number of lazy pages directly influences the busy list length thus
       on operations like: allocation, lookup, unmap, remove, etc.
    
    2) Under heavy stress of vmalloc subsystem I run into a situation when
       memory usage gets increased hitting out_of_memory -> panic state due to
       completely blocking of logic that frees vmap areas in the
       __purge_vmap_area_lazy() function.
    
    Establish a threshold passing which the freeing is prioritized back over
    allocation creating a balance between each other.
    
    Using vmalloc test driver in "stress mode", i.e.  When all available
    test cases are run simultaneously on all online CPUs applying a
    pressure on the vmalloc subsystem, my HiKey 960 board runs out of
    memory due to the fact that __purge_vmap_area_lazy() logic simply is
    not able to free pages in time.
    
    How I run it:
    
    1) You should build your kernel with CONFIG_TEST_VMALLOC=m
    2) ./tools/testing/selftests/vm/test_vmalloc.sh stress
    
    During this test "vmap_lazy_nr" pages will go far beyond acceptable
    lazy_max_pages() threshold, that will lead to enormous busy list size
    and other problems including allocation time and so on.
    
    Link: http://lkml.kernel.org/r/20190124115648.9433-3-urezki@gmail.comSigned-off-by: default avatarUladzislau Rezki (Sony) <urezki@gmail.com>
    Reviewed-by: default avatarAndrew Morton <akpm@linux-foundation.org>
    Cc: Michal Hocko <mhocko@suse.com>
    Cc: Matthew Wilcox <willy@infradead.org>
    Cc: Thomas Garnier <thgarnie@google.com>
    Cc: Oleksiy Avramchenko <oleksiy.avramchenko@sonymobile.com>
    Cc: Steven Rostedt <rostedt@goodmis.org>
    Cc: Joel Fernandes <joelaf@google.com>
    Cc: Thomas Gleixner <tglx@linutronix.de>
    Cc: Ingo Molnar <mingo@elte.hu>
    Cc: Tejun Heo <tj@kernel.org>
    Cc: Joel Fernandes <joel@joelfernandes.org>
    Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
    Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
    68571be9
vmalloc.c 73.3 KB