On Tue, 16 Feb 2010 16:03:23 -0800 (PST)
David Rientjes <rientjes@xxxxxxxxxx> wrote:
> On Wed, 17 Feb 2010, KAMEZAWA Hiroyuki wrote:
>
> > > > > I'll add this check to __alloc_pages_may_oom() for the !(gfp_mask &
> > > > > __GFP_NOFAIL) path since we're all content with endlessly looping.
> > > >
> > > > Thanks. Yes endlessly looping is far preferable to randomly oopsing
> > > > or corrupting memory.
> > > >
> > >
> > > Here's the new patch for your consideration.
> > >
> >
> > Then, can we take kdump in this endlessly looping situaton ?
> >
> > panic_on_oom=always + kdump can do that.
> >
>
> The endless loop is only helpful if something is going to free memory
> external to the current page allocation: either another task with
> __GFP_WAIT | __GFP_FS that invokes the oom killer, a task that frees
> memory, or a task that exits.
>
> The most notable endless loop in the page allocator is the one when a task
> has been oom killed, gets access to memory reserves, and then cannot find
> a page for a __GFP_NOFAIL allocation:
>
> do {
> page = get_page_from_freelist(gfp_mask, nodemask, order,
> zonelist, high_zoneidx, ALLOC_NO_WATERMARKS,
> preferred_zone, migratetype);
>
> if (!page && gfp_mask & __GFP_NOFAIL)
> congestion_wait(BLK_RW_ASYNC, HZ/50);
> } while (!page && (gfp_mask & __GFP_NOFAIL));
>
> We don't expect any such allocations to happen during the exit path, but
> we could probably find some in the fs layer.
>
> I don't want to check sysctl_panic_on_oom in the page allocator because it
> would start panicking the machine unnecessarily for the integrity
> metadata GFP_NOIO | __GFP_NOFAIL allocation, for any
> order > PAGE_ALLOC_COSTLY_ORDER, or for users who can't lock the zonelist
> for oom kill that wouldn't have panicked before.
>
Then, why don't you check higzone_idx in oom_kill.c
Thanks,
-Kame
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