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    SubjectRe: Deadlock possibly caused by too_many_isolated.
    Hello

    On Wed, Oct 20, 2010 at 09:25:49AM +0200, Torsten Kaiser wrote:
    > On Wed, Oct 20, 2010 at 7:57 AM, Wu Fengguang <fengguang.wu@intel.com> wrote:
    > > On Tue, Oct 19, 2010 at 06:06:21PM +0800, Torsten Kaiser wrote:
    > >> swap_writepage() uses get_swap_bio() which uses bio_alloc() to get one
    > >> bio. That bio is the submitted, but the submit path seems to get into
    > >> make_request from raid1.c and that allocates a second bio from
    > >> bio_alloc() via bio_clone().
    > >>
    > >> I am seeing this pattern (swap_writepage calling
    > >> md_make_request/make_request and then getting stuck in mempool_alloc)
    > >> more than 5 times in the SysRq+T output...
    > >
    > > I bet the root cause is the failure of pool->alloc(__GFP_NORETRY)
    > > inside mempool_alloc(), which can be fixed by this patch.
    >
    > No. I tested the patch (ontop of Neils fix and your patch regarding
    > too_many_isolated()), but the system got stuck the same way on the
    > first try to fill the tmpfs.
    > I think the basic problem is, that the mempool that should guarantee
    > progress is exhausted because the raid1 device is stacked between the
    > pageout code and the disks and so the "use only 1 bio"-rule gets
    > violated.
    >
    > > Thanks,
    > > Fengguang
    > > ---
    > >
    > > concurrent direct page reclaim problem
    > >
    > > ?__GFP_NORETRY page allocations may fail when there are many concurrent page
    > > ?allocating tasks, but not necessary in real short of memory. The root cause
    > > ?is, tasks will first run direct page reclaim to free some pages from the LRU
    > > ?lists and put them to the per-cpu page lists and the buddy system, and then
    > > ?try to get a free page from there. ?However the free pages reclaimed by this
    > > ?task may be consumed by other tasks when the direct reclaim task is able to
    > > ?get the free page for itself.
    >
    > I believe the facts disagree with that assumtion. My bad for not
    > posting this before, but I also used SysRq+M to see whats going on,
    > but each time there still was some free memory.
    > Here is the SysRq+M output from the run with only Neils patch applied,
    > but on each other run the same ~14Mb stayed free


    What is your problem?(Sorry if you explained it several time).
    I read the thread.
    It seems Wu's patch solved deadlock problem by FS lock holding and too_many_isolated.
    What is the problem remained in your case? unusable system by swapstorm?
    If it is, I think it's expected behavior. Please see the below comment.
    (If I don't catch your point, Please explain your problem.)

    >
    > [ 437.481365] SysRq : Show Memory
    > [ 437.490003] Mem-Info:
    > [ 437.491357] Node 0 DMA per-cpu:
    > [ 437.500032] CPU 0: hi: 0, btch: 1 usd: 0
    > [ 437.500032] CPU 1: hi: 0, btch: 1 usd: 0
    > [ 437.500032] CPU 2: hi: 0, btch: 1 usd: 0
    > [ 437.500032] CPU 3: hi: 0, btch: 1 usd: 0
    > [ 437.500032] Node 0 DMA32 per-cpu:
    > [ 437.500032] CPU 0: hi: 186, btch: 31 usd: 138
    > [ 437.500032] CPU 1: hi: 186, btch: 31 usd: 30
    > [ 437.500032] CPU 2: hi: 186, btch: 31 usd: 0
    > [ 437.500032] CPU 3: hi: 186, btch: 31 usd: 0
    > [ 437.500032] Node 1 DMA32 per-cpu:
    > [ 437.500032] CPU 0: hi: 186, btch: 31 usd: 0
    > [ 437.500032] CPU 1: hi: 186, btch: 31 usd: 0
    > [ 437.500032] CPU 2: hi: 186, btch: 31 usd: 0
    > [ 437.500032] CPU 3: hi: 186, btch: 31 usd: 0
    > [ 437.500032] Node 1 Normal per-cpu:
    > [ 437.500032] CPU 0: hi: 186, btch: 31 usd: 0
    > [ 437.500032] CPU 1: hi: 186, btch: 31 usd: 0
    > [ 437.500032] CPU 2: hi: 186, btch: 31 usd: 25
    > [ 437.500032] CPU 3: hi: 186, btch: 31 usd: 30
    > [ 437.500032] active_anon:2039 inactive_anon:985233 isolated_anon:682
    > [ 437.500032] active_file:1667 inactive_file:1723 isolated_file:0
    > [ 437.500032] unevictable:0 dirty:0 writeback:25387 unstable:0
    > [ 437.500032] free:3471 slab_reclaimable:2840 slab_unreclaimable:6337
    > [ 437.500032] mapped:1284 shmem:960501 pagetables:523 bounce:0
    > [ 437.500032] Node 0 DMA free:8008kB min:28kB low:32kB high:40kB
    > active_anon:0kB inact
    > ive_anon:7596kB active_file:12kB inactive_file:0kB unevictable:0kB
    > isolated(anon):0kB i
    > solated(file):0kB present:15768kB mlocked:0kB dirty:0kB
    > writeback:404kB mapped:0kB shme
    > m:7192kB slab_reclaimable:32kB slab_unreclaimable:304kB
    > kernel_stack:0kB pagetables:0kB
    > unstable:0kB bounce:0kB writeback_tmp:0kB pages_scanned:118
    > all_unreclaimable? no
    > [ 437.500032] lowmem_reserve[]: 0 2004 2004 2004

    Node 0 DMA : free 8008K but lowmem_reserve 8012K(2004 pages)
    So page allocator can't allocate the page unless preferred zone is DMA

    > [ 437.500032] Node 0 DMA32 free:2980kB min:4036kB low:5044kB
    > high:6052kB active_anon:2
    > 844kB inactive_anon:1918424kB active_file:3428kB inactive_file:3780kB
    > unevictable:0kB isolated(anon):1232kB isolated(file):0kB
    > present:2052320kB mlocked:0kB dirty:0kB writeback:72016kB
    > mapped:2232kB shmem:1847640kB slab_reclaimable:5444kB
    > slab_unreclaimable:13508kB kernel_stack:744kB pagetables:864kB
    > unstable:0kB bounce:0kB writeback_tmp:0kB pages_scanned:0
    > all_unreclaimable? no
    > [ 437.500032] lowmem_reserve[]: 0 0 0 0

    Node 0 DMA32 : free 2980K but min 4036K.
    Few file LRU compare to anon LRU

    Normally, it could fail to allocate the page.
    'Normal' means caller doesn't request alloc_pages with __GFP_HIGH or !__GFP_WAIT
    Generally many call sites don't pass gfp_flag with __GFP_HIGH|!__GFP_WAIT.

    > [ 437.500032] Node 1 DMA32 free:2188kB min:3036kB low:3792kB
    > high:4552kB active_anon:0kB inactive_anon:1555368kB active_file:0kB
    > inactive_file:28kB unevictable:0kB isolated(anon):768kB
    > isolated(file):0kB present:1544000kB mlocked:0kB dirty:0kB
    > writeback:21160kB mapped:0kB shmem:1534960kB slab_reclaimable:3728kB
    > slab_unreclaimable:7076kB kernel_stack:8kB pagetables:0kB unstable:0kB
    > bounce:0kB writeback_tmp:0kB pages_scanned:0 all_unreclaimable? no
    > [ 437.500032] lowmem_reserve[]: 0 0 505 505

    Node 1 DMA32 free : 2188K min 3036K
    It's a same situation with Node 0 DMA32.
    Normally, it could fail to allocate the page.
    Few file LRU compare to anon LRU


    > [ 437.500032] Node 1 Normal free:708kB min:1016kB low:1268kB
    > high:1524kB active_anon:5312kB inactive_anon:459544kB
    > active_file:3228kB inactive_file:3084kB unevictable:0kB
    > isolated(anon):728kB isolated(file):0kB present:517120kB mlocked:0kB
    > dirty:0kB writeback:7968kB mapped:2904kB shmem:452212kB
    > slab_reclaimable:2156kB slab_unreclaimable:4460kB kernel_stack:200kB
    > pagetables:1228kB unstable:0kB bounce:0kB writeback_tmp:0kB
    > pages_scanned:9678 all_unreclaimable? no
    > [ 437.500032] lowmem_reserve[]: 0 0 0 0

    Node 1 Normal : free 708K min 1016K
    Normally, it could fail to allocate the page.
    Few file LRU compare to anon LRU

    > [ 437.500032] Node 0 DMA: 2*4kB 2*8kB 1*16kB 3*32kB 3*64kB 4*128kB
    > 4*256kB 2*512kB 1*1024kB 2*2048kB 0*4096kB = 8008kB
    > [ 437.500032] Node 0 DMA32: 27*4kB 15*8kB 8*16kB 8*32kB 7*64kB
    > 1*128kB 1*256kB 1*512kB 1*1024kB 0*2048kB 0*4096kB = 2980kB
    > [ 437.500032] Node 1 DMA32: 1*4kB 6*8kB 3*16kB 1*32kB 0*64kB 1*128kB
    > 0*256kB 0*512kB 0*1024kB 1*2048kB 0*4096kB = 2308kB
    > [ 437.500032] Node 1 Normal: 39*4kB 13*8kB 10*16kB 3*32kB 1*64kB
    > 1*128kB 0*256kB 0*512kB 0*1024kB 0*2048kB 0*4096kB = 708kB
    > [ 437.500032] 989289 total pagecache pages
    > [ 437.500032] 25398 pages in swap cache
    > [ 437.500032] Swap cache stats: add 859204, delete 833806, find 28/39
    > [ 437.500032] Free swap = 9865628kB
    > [ 437.500032] Total swap = 10000316kB
    > [ 437.500032] 1048575 pages RAM
    > [ 437.500032] 33809 pages reserved
    > [ 437.500032] 7996 pages shared
    > [ 437.500032] 1008521 pages non-shared
    >
    All zones don't have enough pages and don't have enough file lru pages.
    So swapout is expected behavior, I think.
    It means your workload exceeds your system available DRAM size.

    --
    Kind regards,
    Minchan Kim


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