mm: compaction: Use async migration for __GFP_NO_KSWAPD and enforce no writeback

__GFP_NO_KSWAPD allocations are usually very expensive and not mandatory
to succeed as they have graceful fallback.  Waiting for I/O in those,
tends to be overkill in terms of latencies, so we can reduce their latency
by disabling sync migrate.

Unfortunately, even with async migration it's still possible for the
process to be blocked waiting for a request slot (e.g.  get_request_wait
in the block layer) when ->writepage is called.  To prevent
__GFP_NO_KSWAPD blocking, this patch prevents ->writepage being called on
dirty page cache for asynchronous migration.

Addresses https://bugzilla.kernel.org/show_bug.cgi?id=31142

[[email protected]: Avoid writebacks for NFS, retry locked pages, use bool]
Signed-off-by: Andrea Arcangeli <[email protected]>
Signed-off-by: Mel Gorman <[email protected]>
Cc: Arthur Marsh <[email protected]>
Cc: Clemens Ladisch <[email protected]>
Cc: Johannes Weiner <[email protected]>
Cc: KAMEZAWA Hiroyuki <[email protected]>
Cc: Minchan Kim <[email protected]>
Reported-by: Alex Villacis Lasso <[email protected]>
Tested-by: Alex Villacis Lasso <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

0 files changed, 0 insertions, 0 deletions