mm: compaction: move fatal signal check out of compact_checklock_irqsave

mm: compaction: move fatal signal check out of compact_checklock_irqsave

Commit c67fe3752abe ("mm: compaction: Abort async compaction if locks
are contended or taking too long") addressed a lock contention problem
in compaction by introducing compact_checklock_irqsave() that effecively
aborting async compaction in the event of compaction.

To preserve existing behaviour it also moved a fatal_signal_pending()
check into compact_checklock_irqsave() but that is very misleading.  It
"hides" the check within a locking function but has nothing to do with
locking as such.  It just happens to work in a desirable fashion.

This patch moves the fatal_signal_pending() check to
isolate_migratepages_range() where it belongs.  Arguably the same check
should also happen when isolating pages for freeing but it's overkill.

Signed-off-by: Mel Gorman <[email protected]>
Cc: Rik van Riel <[email protected]>
Cc: KAMEZAWA Hiroyuki <[email protected]>
Cc: Shaohua Li <[email protected]>
Cc: Minchan Kim <[email protected]>
Cc: Andrea Arcangeli <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>