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mm: migrate: simplify the logic for handling permanent failure
When unmap_and_move{_huge_page}() returns !-EAGAIN and !MIGRATEPAGE_SUCCESS, the page would be put back to LRU or proper list if it is non-LRU movable page. But, the callers always call putback_movable_pages() to put the failed pages back later on, so it seems not very efficient to put every single page back immediately, and the code looks convoluted. Put the failed page on a separate list, then splice the list to migrate list when all pages are tried. It is the caller's responsibility to call putback_movable_pages() to handle failures. This also makes the code simpler and more readable. After the change the rules are: * Success: non hugetlb page will be freed, hugetlb page will be put back * -EAGAIN: stay on the from list * -ENOMEM: stay on the from list * Other errno: put on ret_pages list then splice to from list The from list would be empty iff all pages are migrated successfully, it was not so before. This has no impact to current existing callsites. Link: https://lkml.kernel.org/r/20201113205359.556831-3-shy828301@gmail.com Signed-off-by: Yang Shi <shy828301@gmail.com> Reviewed-by: Zi Yan <ziy@nvidia.com> Cc: Jan Kara <jack@suse.cz> Cc: Matthew Wilcox <willy@infradead.org> Cc: Mel Gorman <mgorman@suse.de> Cc: Michal Hocko <mhocko@suse.com> Cc: Song Liu <songliubraving@fb.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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Yang Shi
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Linus Torvalds
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Dec 15, 2020
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