Messages in this thread | | | Date | Sun, 27 Jan 2008 21:52:49 -0800 | From | Andrew Morton <> | Subject | Re: [PATCH] Only print kernel debug information for OOMs caused by kernel allocations |
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On Wed, 16 Jan 2008 23:24:21 +0100 Andi Kleen <ak@suse.de> wrote:
> > I recently suffered an 20+ minutes oom thrash disk to death and computer > completely unresponsive situation on my desktop when some user program > decided to grab all memory. It eventually recovered, but left lots > of ugly and imho misleading messages in the kernel log. here's a minor > improvement > > -Andi > > --- > > Only print kernel debug information for OOMs caused by kernel allocations > > For any page cache allocation don't print the backtrace and the detailed > zone debugging information. This makes the problem look less like > a kernel bug because it typically isn't. > > I needed a new task flag for that. Since the bits are running low > I reused an unused one (PF_STARTING) > > Also clarify the error message (OOM means nothing to a normal user) >
That information is useful for working out why a userspace allocation attempt failed. If we don't print it, and the application gets killed and thus frees a lot of memory, we will just never know why the allocation failed.
> struct page *__page_cache_alloc(gfp_t gfp) > { > + struct task_struct *me = current; > + unsigned old = (~me->flags) & PF_USER_ALLOC; > + struct page *p; > + > + me->flags |= PF_USER_ALLOC; > if (cpuset_do_page_mem_spread()) { > int n = cpuset_mem_spread_node(); > - return alloc_pages_node(n, gfp, 0); > - } > - return alloc_pages(gfp, 0); > + p = alloc_pages_node(n, gfp, 0); > + } else > + p = alloc_pages(gfp, 0); > + /* Clear USER_ALLOC if it wasn't set originally */ > + me->flags ^= old; > + return p; > }
That's appreciable amount of new overhead for at best a fairly marginal benefit. Perhaps __GFP_USER could be [re|ab]used.
Alternatively: if we've printed the diagnostic on behalf of this process and then decided to kill it, set some flag to prevent us from printing it again.
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