Hello Dave,
On Thu, May 29, 2014 at 11:58:30AM +1000, Dave Chinner wrote:
> On Thu, May 29, 2014 at 11:30:07AM +1000, Dave Chinner wrote:
> > On Wed, May 28, 2014 at 03:41:11PM -0700, Linus Torvalds wrote:
> > commit a237c1c5bc5dc5c76a21be922dca4826f3eca8ca
> > Author: Jens Axboe <jaxboe@xxxxxxxxxxxx>
> > Date: Sat Apr 16 13:27:55 2011 +0200
> >
> > block: let io_schedule() flush the plug inline
> >
> > Linus correctly observes that the most important dispatch cases
> > are now done from kblockd, this isn't ideal for latency reasons.
> > The original reason for switching dispatches out-of-line was to
> > avoid too deep a stack, so by _only_ letting the "accidental"
> > flush directly in schedule() be guarded by offload to kblockd,
> > we should be able to get the best of both worlds.
> >
> > So add a blk_schedule_flush_plug() that offloads to kblockd,
> > and only use that from the schedule() path.
> >
> > Signed-off-by: Jens Axboe <jaxboe@xxxxxxxxxxxx>
> >
> > And now we have too deep a stack due to unplugging from io_schedule()...
>
> So, if we make io_schedule() push the plug list off to the kblockd
> like is done for schedule()....
>
> > > IOW, swap-out directly caused that extra 3kB of stack use in what was
> > > a deep call chain (due to memory allocation). I really don't
> > > understand why you are arguing anything else on a pure technicality.
> > >
> > > I thought you had some other argument for why swap was different, and
> > > against removing that "page_is_file_cache()" special case in
> > > shrink_page_list().
> >
> > I've said in the past that swap is different to filesystem
> > ->writepage implementations because it doesn't require significant
> > stack to do block allocation and doesn't trigger IO deep in that
> > allocation stack. Hence it has much lower stack overhead than the
> > filesystem ->writepage implementations and so is much less likely to
> > have stack issues.
> >
> > This stack overflow shows us that just the memory reclaim + IO
> > layers are sufficient to cause a stack overflow,
>
> .... we solve this problem directly by being able to remove the IO
> stack usage from the direct reclaim swap path.
>
> IOWs, we don't need to turn swap off at all in direct reclaim
> because all the swap IO can be captured in a plug list and
> dispatched via kblockd. This could be done either by io_schedule()
> or a new blk_flush_plug_list() wrapper that pushes the work to
> kblockd...
I did below hacky test to apply your idea and the result is overflow again.
So, again it would second stack expansion. Otherwise, we should prevent
swapout in direct reclaim.
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index f5c6635b806c..95f169e85dbe 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -4241,10 +4241,13 @@ EXPORT_SYMBOL_GPL(yield_to);
void __sched io_schedule(void)
{
struct rq *rq = raw_rq();
+ struct blk_plug *plug = current->plug;
delayacct_blkio_start();
atomic_inc(&rq->nr_iowait);
- blk_flush_plug(current);
+ if (plug)
+ blk_flush_plug_list(plug, true);
+
current->in_iowait = 1;
schedule();
current->in_iowait = 0;
[ 1209.764725] kworker/u24:0 (23627) used greatest stack depth: 304 bytes left
[ 1510.835509] kworker/u24:1 (25817) used greatest stack depth: 144 bytes left
[ 3701.482790] PANIC: double fault, error_code: 0x0
[ 3701.483297] CPU: 8 PID: 6117 Comm: kworker/u24:1 Not tainted 3.14.0+ #201
[ 3701.483980] Hardware name: Bochs Bochs, BIOS Bochs 01/01/2011
[ 3701.484366] Workqueue: writeback bdi_writeback_workfn (flush-253:0)
[ 3701.484366] task: ffff8800353c41c0 ti: ffff880000106000 task.ti: ffff880000106000
[ 3701.484366] RIP: 0010:[<ffffffff810a5390>] [<ffffffff810a5390>] __lock_acquire+0x170/0x1ca0
[ 3701.484366] RSP: 0000:ffff880000105f58 EFLAGS: 00010046
[ 3701.484366] RAX: 0000000000000001 RBX: ffff8800353c41c0 RCX: 0000000000000002
[ 3701.484366] RDX: 0000000000000000 RSI: 0000000000000000 RDI: ffffffff81c4a1e0
[ 3701.484366] RBP: ffff880000106048 R08: 0000000000000001 R09: 0000000000000001
[ 3701.484366] R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000001
[ 3701.484366] R13: 0000000000000000 R14: ffffffff81c4a1e0 R15: 0000000000000000
[ 3701.484366] FS: 0000000000000000(0000) GS:ffff880037d00000(0000) knlGS:0000000000000000
[ 3701.484366] CS: 0010 DS: 0000 ES: 0000 CR0: 000000008005003b
[ 3701.484366] CR2: ffff880000105f48 CR3: 0000000001c0b000 CR4: 00000000000006e0
[ 3701.484366] Stack:
[ 3701.484366] BUG: unable to handle kernel paging request at ffff880000105f58
[ 3701.484366] IP: [<ffffffff81004e14>] show_stack_log_lvl+0x134/0x1a0
[ 3701.484366] PGD 28c5067 PUD 28c6067 PMD 28c7067 PTE 8000000000105060
[ 3701.484366] Thread overran stack, or stack corrupted
[ 3701.484366] Oops: 0000 [#1] SMP DEBUG_PAGEALLOC
[ 3701.484366] Dumping ftrace buffer:
[ 3701.484366] ---------------------------------
[ 3701.484366] <...>-6117 8d..4 3786719374us : stack_trace_call: Depth Size Location (46 entries)
[ 3701.484366] ----- ---- --------
[ 3701.484366] <...>-6117 8d..4 3786719395us : stack_trace_call: 0) 7200 8 _raw_spin_lock_irqsave+0x51/0x60
[ 3701.484366] <...>-6117 8d..4 3786719395us : stack_trace_call: 1) 7192 296 get_page_from_freelist+0x886/0x920
[ 3701.484366] <...>-6117 8d..4 3786719395us : stack_trace_call: 2) 6896 352 __alloc_pages_nodemask+0x5e1/0xb20
[ 3701.484366] <...>-6117 8d..4 3786719396us : stack_trace_call: 3) 6544 8 alloc_pages_current+0x10f/0x1f0
[ 3701.484366] <...>-6117 8d..4 3786719396us : stack_trace_call: 4) 6536 168 new_slab+0x2c5/0x370
[ 3701.484366] <...>-6117 8d..4 3786719396us : stack_trace_call: 5) 6368 8 __slab_alloc+0x3a9/0x501
[ 3701.484366] <...>-6117 8d..4 3786719396us : stack_trace_call: 6) 6360 80 __kmalloc+0x1cb/0x200
[ 3701.484366] <...>-6117 8d..4 3786719396us : stack_trace_call: 7) 6280 376 vring_add_indirect+0x36/0x200
[ 3701.484366] <...>-6117 8d..4 3786719397us : stack_trace_call: 8) 5904 144 virtqueue_add_sgs+0x2e2/0x320
[ 3701.484366] <...>-6117 8d..4 3786719397us : stack_trace_call: 9) 5760 288 __virtblk_add_req+0xda/0x1b0
[ 3701.484366] <...>-6117 8d..4 3786719397us : stack_trace_call: 10) 5472 96 virtio_queue_rq+0xd3/0x1d0
[ 3701.484366] <...>-6117 8d..4 3786719397us : stack_trace_call: 11) 5376 128 __blk_mq_run_hw_queue+0x1ef/0x440
[ 3701.484366] <...>-6117 8d..4 3786719397us : stack_trace_call: 12) 5248 16 blk_mq_run_hw_queue+0x35/0x40
[ 3701.484366] <...>-6117 8d..4 3786719397us : stack_trace_call: 13) 5232 96 blk_mq_insert_requests+0xdb/0x160
[ 3701.484366] <...>-6117 8d..4 3786719398us : stack_trace_call: 14) 5136 112 blk_mq_flush_plug_list+0x12b/0x140
[ 3701.484366] <...>-6117 8d..4 3786719398us : stack_trace_call: 15) 5024 112 blk_flush_plug_list+0xc7/0x220
[ 3701.484366] <...>-6117 8d..4 3786719398us : stack_trace_call: 16) 4912 128 blk_mq_make_request+0x42a/0x600
[ 3701.484366] <...>-6117 8d..4 3786719398us : stack_trace_call: 17) 4784 48 generic_make_request+0xc0/0x100
[ 3701.484366] <...>-6117 8d..4 3786719398us : stack_trace_call: 18) 4736 112 submit_bio+0x86/0x160
[ 3701.484366] <...>-6117 8d..4 3786719398us : stack_trace_call: 19) 4624 160 __swap_writepage+0x198/0x230
[ 3701.484366] <...>-6117 8d..4 3786719399us : stack_trace_call: 20) 4464 32 swap_writepage+0x42/0x90
[ 3701.484366] <...>-6117 8d..4 3786719399us : stack_trace_call: 21) 4432 320 shrink_page_list+0x676/0xa80
[ 3701.484366] <...>-6117 8d..4 3786719399us : stack_trace_call: 22) 4112 208 shrink_inactive_list+0x262/0x4e0
[ 3701.484366] <...>-6117 8d..4 3786719399us : stack_trace_call: 23) 3904 304 shrink_lruvec+0x3e1/0x6a0
[ 3701.484366] <...>-6117 8d..4 3786719399us : stack_trace_call: 24) 3600 80 shrink_zone+0x3f/0x110
[ 3701.484366] <...>-6117 8d..4 3786719400us : stack_trace_call: 25) 3520 128 do_try_to_free_pages+0x156/0x4c0
[ 3701.484366] <...>-6117 8d..4 3786719400us : stack_trace_call: 26) 3392 208 try_to_free_pages+0xf7/0x1e0
[ 3701.484366] <...>-6117 8d..4 3786719400us : stack_trace_call: 27) 3184 352 __alloc_pages_nodemask+0x783/0xb20
[ 3701.484366] <...>-6117 8d..4 3786719400us : stack_trace_call: 28) 2832 8 alloc_pages_current+0x10f/0x1f0
[ 3701.484366] <...>-6117 8d..4 3786719400us : stack_trace_call: 29) 2824 200 __page_cache_alloc+0x13f/0x160
[ 3701.484366] <...>-6117 8d..4 3786719400us : stack_trace_call: 30) 2624 80 find_or_create_page+0x4c/0xb0
[ 3701.484366] <...>-6117 8d..4 3786719401us : stack_trace_call: 31) 2544 112 __getblk+0x109/0x2f0
[ 3701.484366] <...>-6117 8d..4 3786719401us : stack_trace_call: 32) 2432 224 ext4_ext_insert_extent+0x4d8/0x1270
[ 3701.484366] <...>-6117 8d..4 3786719401us : stack_trace_call: 33) 2208 256 ext4_ext_map_blocks+0x8d4/0x1010
[ 3701.484366] <...>-6117 8d..4 3786719401us : stack_trace_call: 34) 1952 160 ext4_map_blocks+0x325/0x530
[ 3701.484366] <...>-6117 8d..4 3786719401us : stack_trace_call: 35) 1792 384 ext4_writepages+0x6d1/0xce0
[ 3701.484366] <...>-6117 8d..4 3786719402us : stack_trace_call: 36) 1408 16 do_writepages+0x23/0x40
[ 3701.484366] <...>-6117 8d..4 3786719402us : stack_trace_call: 37) 1392 96 __writeback_single_inode+0x45/0x2e0
[ 3701.484366] <...>-6117 8d..4 3786719402us : stack_trace_call: 38) 1296 176 writeback_sb_inodes+0x2ad/0x500
[ 3701.484366] <...>-6117 8d..4 3786719402us : stack_trace_call: 39) 1120 80 __writeback_inodes_wb+0x9e/0xd0
[ 3701.484366] <...>-6117 8d..4 3786719402us : stack_trace_call: 40) 1040 160 wb_writeback+0x29b/0x350
[ 3701.484366] <...>-6117 8d..4 3786719402us : stack_trace_call: 41) 880 208 bdi_writeback_workfn+0x11c/0x480
[ 3701.484366] <...>-6117 8d..4 3786719403us : stack_trace_call: 42) 672 144 process_one_work+0x1d2/0x570
[ 3701.484366] <...>-6117 8d..4 3786719403us : stack_trace_call: 43) 528 112 worker_thread+0x116/0x370
[ 3701.484366] <...>-6117 8d..4 3786719403us : stack_trace_call: 44) 416 240 kthread+0xf3/0x110
[ 3701.484366] <...>-6117 8d..4 3786719403us : stack_trace_call: 45) 176 176 ret_from_fork+0x7c/0xb0
[ 3701.484366] ---------------------------------
[ 3701.484366] Modules linked in:
[ 3701.484366] CPU: 8 PID: 6117 Comm: kworker/u24:1 Not tainted 3.14.0+ #201
[ 3701.484366] Hardware name: Bochs Bochs, BIOS Bochs 01/01/2011
[ 3701.484366] Workqueue: writeback bdi_writeback_workfn (flush-253:0)
[ 3701.484366] task: ffff8800353c41c0 ti: ffff880000106000 task.ti: ffff880000106000
[ 3701.484366] RIP: 0010:[<ffffffff81004e14>] [<ffffffff81004e14>] show_stack_log_lvl+0x134/0x1a0
[ 3701.484366] RSP: 0000:ffff880037d06e58 EFLAGS: 00010046
[ 3701.484366] RAX: 000000000000000c RBX: 0000000000000000 RCX: 0000000000000000
[ 3701.484366] RDX: ffff880037cfffc0 RSI: ffff880037d06f58 RDI: 0000000000000000
[ 3701.484366] RBP: ffff880037d06ea8 R08: ffffffff81a0804c R09: 0000000000000000
[ 3701.484366] R10: 0000000000000002 R11: 0000000000000002 R12: ffff880037d06f58
[ 3701.484366] R13: 0000000000000000 R14: ffff880000105f58 R15: ffff880037d03fc0
[ 3701.484366] FS: 0000000000000000(0000) GS:ffff880037d00000(0000) knlGS:0000000000000000
[ 3701.484366] CS: 0010 DS: 0000 ES: 0000 CR0: 000000008005003b
[ 3701.484366] CR2: ffff880000105f58 CR3: 0000000001c0b000 CR4: 00000000000006e0
[ 3701.484366] Stack:
[ 3701.484366] 0000000000000000 ffff880000105f58 ffff880037d06f58 ffff880000105f58
[ 3701.484366] ffff880000106000 ffff880037d06f58 0000000000000040 ffff880037d06f58
[ 3701.484366] ffff880000105f58 0000000000000000 ffff880037d06ef8 ffffffff81004f1c
[ 3701.484366] Call Trace:
[ 3701.484366] <#DF>
[ 3701.484366] [<ffffffff81004f1c>] show_regs+0x9c/0x1f0
[ 3701.484366] [<ffffffff8103aa37>] df_debug+0x27/0x40
[ 3701.484366] [<ffffffff81003361>] do_double_fault+0x61/0x80
[ 3701.484366] [<ffffffff816f0907>] double_fault+0x27/0x30
[ 3701.484366] [<ffffffff810a5390>] ? __lock_acquire+0x170/0x1ca0
[ 3701.484366] <<EOE>>
--
Kind regards,
Minchan Kim
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