• Gu Zheng's avatar
    aio: fix uncorrent dirty pages accouting when truncating AIO ring buffer · c60aa7e8
    Gu Zheng authored
    commit 835f252c upstream.
    
    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: default avatarMarkus Königshaus <m.koenigshaus@wut.de>
    Signed-off-by: default avatarGu Zheng <guz.fnst@cn.fujitsu.com>
    Acked-by: default avatarAndrew Morton <akpm@linux-foundation.org>
    Signed-off-by: default avatarBenjamin LaHaise <bcrl@kvack.org>
    Signed-off-by: default avatarLuis Henriques <luis.henriques@canonical.com>
    c60aa7e8
aio.c 42.5 KB