On Wed, 16 Jan 2008 23:24:21 +0100 Andi Kleen <[EMAIL PROTECTED]> 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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