On Sat, Jul 02, 2022 at 09:43:32AM -0600, Jens Axboe wrote: > If we're creating a page cache page with FGP_CREAT but FGP_NOWAIT is > set, we should dial back the gfp flags to avoid frivolous blocking > which is trivial to hit in low memory conditions: > > [ 10.117661] __schedule+0x8c/0x550 > [ 10.118305] schedule+0x58/0xa0 > [ 10.118897] schedule_timeout+0x30/0xdc > [ 10.119610] __wait_for_common+0x88/0x114 > [ 10.120348] wait_for_completion+0x1c/0x24 > [ 10.121103] __flush_work.isra.0+0x16c/0x19c > [ 10.121896] flush_work+0xc/0x14 > [ 10.122496] __drain_all_pages+0x144/0x218 > [ 10.123267] drain_all_pages+0x10/0x18 > [ 10.123941] __alloc_pages+0x464/0x9e4 > [ 10.124633] __folio_alloc+0x18/0x3c > [ 10.125294] __filemap_get_folio+0x17c/0x204 > [ 10.126084] iomap_write_begin+0xf8/0x428 > [ 10.126829] iomap_file_buffered_write+0x144/0x24c > [ 10.127710] xfs_file_buffered_write+0xe8/0x248 > [ 10.128553] xfs_file_write_iter+0xa8/0x120 > [ 10.129324] io_write+0x16c/0x38c > [ 10.129940] io_issue_sqe+0x70/0x1cc > [ 10.130617] io_queue_sqe+0x18/0xfc > [ 10.131277] io_submit_sqes+0x5d4/0x600 > [ 10.131946] __arm64_sys_io_uring_enter+0x224/0x600 > [ 10.132752] invoke_syscall.constprop.0+0x70/0xc0 > [ 10.133616] do_el0_svc+0xd0/0x118 > [ 10.134238] el0_svc+0x78/0xa0 > > Clear IO, FS, and reclaim flags and mark the allocation as GFP_NOWAIT and > add __GFP_NOWARN to avoid polluting dmesg with pointless allocations > failures. A caller with FGP_NOWAIT must be expected to handle the > resulting -EAGAIN return and retry from a suitable context without NOWAIT > set. > > Signed-off-by: Jens Axboe <axboe@xxxxxxxxx> Reviewed-by: Shakeel Butt <shakeelb@xxxxxxxxxx>
