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mm: fix free page check in zone_watermark_ok()
__zone_watermark_ok currently compares free_pages which is a signed type with z->lowmem_reserve[classzone_idx] which is unsigned which might lead to sign overflow if free_pages doesn't satisfy the given order (or it came as negative already) and then we rely on the following order loop to fix it (which doesn't work for order-0). Let's fix the type conversion and do not rely on the given value of free_pages or follow up fixups. This patch fixes it because "memory-hotplug: fix kswapd looping forever problem" depends on this. As benefit of this patch, it doesn't rely on the loop to exit __zone_watermark_ok in case of high order check and make the first test effective.(ie, if (free_pages <= min + lowmem_reserve)) Aaditya reported this problem when he test my hotplug patch. Reported-off-by: Aaditya Kumar <[email protected]> Tested-by: Aaditya Kumar <[email protected]> Signed-off-by: Aaditya Kumar <[email protected]> Signed-off-by: Minchan Kim <[email protected]> Cc: KOSAKI Motohiro <[email protected]> Cc: KAMEZAWA Hiroyuki <[email protected]> Cc: Mel Gorman <[email protected]> Reviewed-by: Michal Hocko <[email protected]> Signed-off-by: Andrew Morton <[email protected]> Signed-off-by: Linus Torvalds <[email protected]>
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