• Joonsoo Kim's avatar
    mm/page_ext: resurrect struct page extending code for debugging · eefa864b
    Joonsoo Kim authored
    When we debug something, we'd like to insert some information to every
    page.  For this purpose, we sometimes modify struct page itself.  But,
    this has drawbacks.  First, it requires re-compile.  This makes us
    hesitate to use the powerful debug feature so development process is
    slowed down.  And, second, sometimes it is impossible to rebuild the
    kernel due to third party module dependency.  At third, system behaviour
    would be largely different after re-compile, because it changes size of
    struct page greatly and this structure is accessed by every part of
    kernel.  Keeping this as it is would be better to reproduce errornous
    situation.
    
    This feature is intended to overcome above mentioned problems.  This
    feature allocates memory for extended data per page in certain place
    rather than the struct page itself.  This memory can be accessed by the
    accessor functions provided by this code.  During the boot process, it
    checks whether allocation of huge chunk of memory is needed or not.  If
    not, it avoids allocating memory at all.  With this advantage, we can
    include this feature into the kernel in default and can avoid rebuild and
    solve related problems.
    
    Until now, memcg uses this technique.  But, now, memcg decides to embed
    their variable to struct page itself and it's code to extend struct page
    has been removed.  I'd like to use this code to develop debug feature, so
    this patch resurrect it.
    
    To help these things to work well, this patch introduces two callbacks for
    clients.  One is the need callback which is mandatory if user wants to
    avoid useless memory allocation at boot-time.  The other is optional, init
    callback, which is used to do proper initialization after memory is
    allocated.  Detailed explanation about purpose of these functions is in
    code comment.  Please refer it.
    
    Others are completely same with previous extension code in memcg.
    Signed-off-by: default avatarJoonsoo Kim <iamjoonsoo.kim@lge.com>
    Cc: Mel Gorman <mgorman@suse.de>
    Cc: Johannes Weiner <hannes@cmpxchg.org>
    Cc: Minchan Kim <minchan@kernel.org>
    Cc: Dave Hansen <dave@sr71.net>
    Cc: Michal Nazarewicz <mina86@mina86.com>
    Cc: Jungsoo Son <jungsoo.son@lge.com>
    Cc: Ingo Molnar <mingo@redhat.com>
    Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
    Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
    Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
    eefa864b
page_ext.c 10.1 KB