| Message ID | dd47b882-1a18-317c-9906-e73c5487678c@kernel.dk (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | [v2] mm: honor FGP_NOWAIT for page cache page allocation | expand |
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@kernel.dk> Reviewed-by: Shakeel Butt <shakeelb@google.com>
On Sat, Jul 02, 2022 at 09:43:32AM -0600, Jens Axboe wrote: > +++ 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; > + gfp |= GFP_NOWAIT | __GFP_NOWARN; > + } Wouldn't it be simpler to write: if (fgp_flags & FGP_NOWAIT) { gfp &= ~__GFP_DIRECT_RECLAIM; gfp |= __GFP_NOWARN; } (I'd prefer it if the caller passed in the GFP flags that it actually wants, but looking at the patches that prompted this, that seems rather annoying to do)
On 7/3/22 2:37 AM, Matthew Wilcox wrote: > On Sat, Jul 02, 2022 at 09:43:32AM -0600, Jens Axboe wrote: >> +++ 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; >> + gfp |= GFP_NOWAIT | __GFP_NOWARN; >> + } > > Wouldn't it be simpler to write: > > if (fgp_flags & FGP_NOWAIT) { > gfp &= ~__GFP_DIRECT_RECLAIM; > gfp |= __GFP_NOWARN; > } That won't clear IO or FS, though? We really just want GFP_NOWAIT | __GFP_NOWARN here, but didn't want to make assumptions on whatever else would be set in gfp already. > (I'd prefer it if the caller passed in the GFP flags that it actually > wants, but looking at the patches that prompted this, that seems rather > annoying to do) Yes me too, but that's a lot of annoying churn...
diff --git a/mm/filemap.c b/mm/filemap.c index ffdfbc8b0e3c..254931a6e3ed 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; + gfp |= GFP_NOWAIT | __GFP_NOWARN; + } folio = filemap_alloc_folio(gfp, 0); if (!folio)
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@kernel.dk> --- V2: - Improve commit message - Add GFP_NOWAIT to allow kswapd wakeup mm/filemap.c | 4 ++++ 1 file changed, 4 insertions(+)