per_cpu_pages_init() sets pcp->batch to 1 (BOOT_PAGESET_BATCH) at boot, then later it is set to 0 (from zone_batchsize()) via the following path: init_per_zone_wmark_min() ->setup_per_zone_wmarks() ->zone_pcp_update() ->zone_set_pageset_high_and_batch() Once this happens if an OOM happens drain_pages_zone() will never return because count never gets to zero. Signed-off-by: Daniel Palmer --- Background: I am running a nommu kernel on 68000 with 8MB of RAM, I messed up my userland config and the resulting binaries became too big to fit in to the free blocks of memory, OOM should have happened and I should have seen the kernel trying to free memory but instead it dead locked. Since this is nommu I thought maybe I am corrupting memory but I checked with gdb and it doesn't seem like it. I have some local patches to make this weird setup work too but I don't think its anything to do with that either. This change stops the dead lock and I see OOM messages instead as expected. I have no idea if it is correct. Patch is simply to show what I am seeing. mm/page_alloc.c | 7 +++++-- 1 file changed, 5 insertions(+), 2 deletions(-) diff --git a/mm/page_alloc.c b/mm/page_alloc.c index 822e05f1a964..83c9ce6f93ad 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -2618,8 +2618,11 @@ static void drain_pages_zone(unsigned int cpu, struct zone *zone) spin_lock(&pcp->lock); count = pcp->count; if (count) { - int to_drain = min(count, - pcp->batch << CONFIG_PCP_BATCH_SCALE_MAX); + int to_drain = count; + + /* if pcp->batch is zero this loop will never exit, on nommu pcp->batch is always 0 */ + if (likely(pcp->batch)) + to_drain = min(count, pcp->batch << CONFIG_PCP_BATCH_SCALE_MAX); free_pcppages_bulk(zone, to_drain, pcp, 0); count -= to_drain; -- 2.51.0