https://bugzilla.kernel.org/show_bug.cgi?id=86831



Markus reported that when shutting down mysqld (with AIO support,
on a ext3 formatted Harddrive) leads to a negative number of dirty pages
(underrun to the counter). The negative number results in a drastic reduction
of the write performance because the page cache is not used, because the kernel
thinks it is still 2 ^ 32 dirty pages open.

Add a warn trace in __dec_zone_state will catch this easily:

static inline void __dec_zone_state(struct zone *zone, enum
	zone_stat_item item)
{
     atomic_long_dec(&zone->vm_stat[item]);
+    WARN_ON_ONCE(item == NR_FILE_DIRTY &&
	atomic_long_read(&zone->vm_stat[item]) < 0);
     atomic_long_dec(&vm_stat[item]);
}

[   21.341632] ------------[ cut here ]------------
[   21.346294] WARNING: CPU: 0 PID: 309 at include/linux/vmstat.h:242
cancel_dirty_page+0x164/0x224()
[   21.355296] Modules linked in: wutbox_cp sata_mv
[   21.359968] CPU: 0 PID: 309 Comm: kworker/0:1 Not tainted 3.14.21-WuT #80
[   21.366793] Workqueue: events free_ioctx
[   21.370760] [<c0016a64>] (unwind_backtrace) from [<c0012f88>]
(show_stack+0x20/0x24)
[   21.378562] [<c0012f88>] (show_stack) from [<c03f8ccc>]
(dump_stack+0x24/0x28)
[   21.385840] [<c03f8ccc>] (dump_stack) from [<c0023ae4>]
(warn_slowpath_common+0x84/0x9c)
[   21.393976] [<c0023ae4>] (warn_slowpath_common) from [<c0023bb8>]
(warn_slowpath_null+0x2c/0x34)
[   21.402800] [<c0023bb8>] (warn_slowpath_null) from [<c00c0688>]
(cancel_dirty_page+0x164/0x224)
[   21.411524] [<c00c0688>] (cancel_dirty_page) from [<c00c080c>]
(truncate_inode_page+0x8c/0x158)
[   21.420272] [<c00c080c>] (truncate_inode_page) from [<c00c0a94>]
(truncate_inode_pages_range+0x11c/0x53c)
[   21.429890] [<c00c0a94>] (truncate_inode_pages_range) from
[<c00c0f6c>] (truncate_pagecache+0x88/0xac)
[   21.439252] [<c00c0f6c>] (truncate_pagecache) from [<c00c0fec>]
(truncate_setsize+0x5c/0x74)
[   21.447731] [<c00c0fec>] (truncate_setsize) from [<c013b3a8>]
(put_aio_ring_file.isra.14+0x34/0x90)
[   21.456826] [<c013b3a8>] (put_aio_ring_file.isra.14) from
[<c013b424>] (aio_free_ring+0x20/0xcc)
[   21.465660] [<c013b424>] (aio_free_ring) from [<c013b4f4>]
(free_ioctx+0x24/0x44)
[   21.473190] [<c013b4f4>] (free_ioctx) from [<c003d8d8>]
(process_one_work+0x134/0x47c)
[   21.481132] [<c003d8d8>] (process_one_work) from [<c003e988>]
(worker_thread+0x130/0x414)
[   21.489350] [<c003e988>] (worker_thread) from [<c00448ac>]
(kthread+0xd4/0xec)
[   21.496621] [<c00448ac>] (kthread) from [<c000ec18>]
(ret_from_fork+0x14/0x20)
[   21.503884] ---[ end trace 79c4bf42c038c9a1 ]---

The cause is that we set the aio ring file pages as *DIRTY* via SetPageDirty
(bypasses the VFS dirty pages increment) when init, and aio fs uses
*default_backing_dev_info* as the backing dev, which does not disable
the dirty pages accounting capability.
So truncating aio ring file will contribute to accounting dirty pages (VFS
dirty pages decrement), then error occurs.

The original goal is keeping these pages in memory (can not be reclaimed
or swapped) in life-time via marking it dirty. But thinking more, we have
already pinned pages via elevating the page's refcount, which can already
achieve the goal, so the SetPageDirty seems unnecessary.

In order to fix the issue, using the __set_page_dirty_no_writeback instead
of the nop .set_page_dirty, and dropped the SetPageDirty (don't manually
set the dirty flags, don't disable set_page_dirty(), rely on default behaviour).

With the above change, the dirty pages accounting can work well. But as we
known, aio fs is an anonymous one, which should never cause any real write-back,
we can ignore the dirty pages (write back) accounting by disabling the dirty
pages (write back) accounting capability. So we introduce an aio private
backing dev info (disabled the ACCT_DIRTY/WRITEBACK/ACCT_WB capabilities) to
replace the default one.

Reported-by: Markus Königshaus <m.koenigshaus@wut.de>
Signed-off-by: Gu Zheng <guz.fnst@cn.fujitsu.com>
Cc: stable <stable@vger.kernel.org>
Acked-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Benjamin LaHaise <bcrl@kvack.org>