On Fri, Jul 01, 2022 at 02:08:26PM -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 nowarn,
> as FGP_NOWAIT are expected to be able to handle -EAGAIN failures and
> retry from a suitable context without NOWAIT set.
>
> Signed-off-by: Jens Axboe <axboe@xxxxxxxxx>
> ---
> mm/filemap.c | 4 ++++
> 1 file changed, 4 insertions(+)
>
> diff --git a/mm/filemap.c b/mm/filemap.c
> index ffdfbc8b0e3c..9b747d3247c6 100644
> --- a/mm/filemap.c
> +++ b/mm/filemap.c
> @@ -1988,6 +1988,10 @@ struct folio *__filemap_get_folio(struct address_space *mapping, pgoff_t index,
> gfp |= __GFP_WRITE;
> if (fgp_flags & FGP_NOFS)
> gfp &= ~__GFP_FS;
> + if (fgp_flags & FGP_NOWAIT) {
> + gfp &= ~GFP_KERNEL;
Do you think the semantic of FGP_NOWAIT should be similar to GFP_NOWAIT?
That is allow kswapd wakeup.
> + gfp |= __GFP_NOWARN;
> + }
>
> folio = filemap_alloc_folio(gfp, 0);
> if (!folio)
> --
> 2.35.1
>
> --
> Jens Axboe
>
>
