> On Jul 1, 2022, at 6:56 PM, Shakeel Butt <shakeelb@xxxxxxxxxx> wrote:
>
> 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.
Yep I think that’d be fine, and probably appropriate.
