lkml.org 
[lkml]   [2012]   [Feb]   [29]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH] mm: SLAB Out-of-memory diagnostics
On Wed, Feb 29, 2012 at 09:37:23AM +0200, Pekka Enberg wrote:
> On Wed, 29 Feb 2012, Rafael Aquini wrote:
> > Following the example at mm/slub.c, add out-of-memory diagnostics to the SLAB
> > allocator to help on debugging OOM conditions. This patch also adds a new
> > sysctl, 'oom_dump_slabs_forced', that overrides the effect of __GFP_NOWARN page
> > allocation flag and forces the kernel to report every slab allocation failure.
> >
> > An example print out looks like this:
> >
> > <snip page allocator out-of-memory message>
> > SLAB: Unable to allocate memory on node 0 (gfp=0x11200)
> > cache: bio-0, object size: 192, order: 0
> > node0: slabs: 3/3, objs: 60/60, free: 0
> >
> > Signed-off-by: Rafael Aquini <aquini@redhat.com>
> > ---
> > Documentation/sysctl/vm.txt | 23 ++++++++++++++++++
> > include/linux/slab.h | 2 +
> > kernel/sysctl.c | 9 +++++++
> > mm/slab.c | 55 ++++++++++++++++++++++++++++++++++++++++++-
> > 4 files changed, 88 insertions(+), 1 deletions(-)
>
> No SLUB support for this?

SLUB already has its version of slab_out_of_memory. I did not propose the sysctl
knob for slub, however. (If we find the knob useful, I can propose its extention
to slub, later).

>
> > diff --git a/Documentation/sysctl/vm.txt b/Documentation/sysctl/vm.txt
> > index 96f0ee8..75bdf91 100644
> > --- a/Documentation/sysctl/vm.txt
> > +++ b/Documentation/sysctl/vm.txt
> > @@ -498,6 +498,29 @@ this is causing problems for your system/application.
> >
> > ==============================================================
> >
> > +oom_dump_slabs_forced
> > +
> > +Overrides the effects of __GFP_NOWARN page allocation flag, thus forcing
> > +the system to print warnings about every allocation failure for the
> > +slab allocator, and helping on debugging certain OOM conditions.
> > +The print out is pretty similar, and complements data that is reported by
> > +the page allocator out-of-memory warning:
> > +
> > +<snip page allocator out-of-memory message>
> > + SLAB: Unable to allocate memory on node 0 (gfp=0x11200)
> > + cache: bio-0, object size: 192, order: 0
> > + node0: slabs: 3/3, objs: 60/60, free: 0
> > +
> > +If this is set to zero, the default behavior is observed and warnings will only
> > +be printed out for allocation requests that didn't set the __GFP_NOWARN flag.
> > +
> > +When set to non-zero, this information is shown whenever the allocator finds
> > +itself failing to grant a request, regardless the __GFP_NOWARN flag status.
> > +
> > +The default value is 0 (disabled).
> > +
> > +==============================================================
> > +
>
> Why do you want to add a sysctl for this? That'd be an ABI that we need to
> keep around forever.
>
> Is there any reason we shouldn't just enable this unconditionally?

I was afraid of this code becoming a source of garrulous and scaring warnings
by just ignoring __GFP_NOWARN flag, however, I was also concerned with the
'hiding' effect the flag imposes for certain requests, specially when one is
interested in checking all those requests out. Therefore, I thought a sysctl
knob would be the best option to control the __GFP_NOWARN overriding behavior of
slab_out_of_memory printouts without messing with the allocation flags
themselves, as well as not imposing the need for reboots to start checking all
slab allocation failures out.

Rafael


\
 
 \ /
  Last update: 2012-02-29 19:51    [from the cache]
©2003-2011 Jasper Spaans