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@xxxxxxxxxx> > > --- > > 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 -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>