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mm/swapfile: add cond_resched() in get_swap_pages()
The softlockup still occurs in get_swap_pages() under memory pressure. 64 CPU cores, 64GB memory, and 28 zram devices, the disksize of each zram device is 50MB with same priority as si. Use the stress-ng tool to increase memory pressure, causing the system to oom frequently. The plist_for_each_entry_safe() loops in get_swap_pages() could reach tens of thousands of times to find available space (extreme case: cond_resched() is not called in scan_swap_map_slots()). Let's add cond_resched() into get_swap_pages() when failed to find available space to avoid softlockup. Link: https://lkml.kernel.org/r/[email protected] Signed-off-by: Longlong Xia <[email protected]> Reviewed-by: "Huang, Ying" <[email protected]> Cc: Chen Wandun <[email protected]> Cc: Huang Ying <[email protected]> Cc: Kefeng Wang <[email protected]> Cc: Nanyong Sun <[email protected]> Cc: Hugh Dickins <[email protected]> Cc: <[email protected]> Signed-off-by: Andrew Morton <[email protected]>