Messages in this thread | | | Date | Tue, 16 Feb 2010 16:03:23 -0800 (PST) | From | David Rientjes <> | Subject | Re: [patch -mm 8/9 v2] oom: avoid oom killer for lowmem allocations |
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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.
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