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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