Messages in this thread | | | Subject | Re: [PATCH] mm: thp: use down_read_trylock in khugepaged to avoid long block | From | "Yang Shi" <> | Date | Sun, 17 Dec 2017 06:22:20 +0800 |
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On 12/16/17 12:09 PM, Kirill A. Shutemov wrote: > On Sat, Dec 16, 2017 at 12:45:25PM +0100, Michal Hocko wrote: >> On Sat 16-12-17 04:04:10, Yang Shi wrote: >>> Hi Kirill & Michal, >>> >>> Since both of you raised the same question about who holds the semaphore for >>> that long time, I just reply here to both of you. >>> >>> The backtrace shows vm-scalability is running with 300G memory and it is >>> doing munmap as below: >>> >>> [188995.241865] CPU: 15 PID: 8063 Comm: usemem Tainted: G E >>> 4.9.65-006.ali3000.alios7.x86_64 #1 >>> [188995.242252] Hardware name: Huawei Technologies Co., Ltd. Tecal RH2288H >>> V2-12L/BC11SRSG1, BIOS RMIBV368 11/01/2013 >>> [188995.242637] task: ffff883f610a5b00 task.stack: ffffc90037280000 >>> [188995.242838] RIP: 0010:[<ffffffff811e2319>] .c [<ffffffff811e2319>] >>> unmap_page_range+0x619/0x940 >>> [188995.243231] RSP: 0018:ffffc90037283c98 EFLAGS: 00000282 >>> [188995.243429] RAX: 00002b760ac57000 RBX: 00002b760ac56000 RCX: >>> 0000000003eb13ca >>> [188995.243820] RDX: ffffea003971e420 RSI: 00002b760ac56000 RDI: >>> ffff8837cb832e80 >>> [188995.244211] RBP: ffffc90037283d78 R08: ffff883ebf8fc3c0 R09: >>> 0000000000008000 >>> [188995.244600] R10: 00000000826b7e00 R11: 0000000000000000 R12: >>> ffff8821e70f72b0 >>> [188995.244993] R13: ffffea00fac4f280 R14: ffffc90037283e00 R15: >>> 00002b760ac57000 >>> [188995.245390] FS: 00002b34b4861700(0000) GS:ffff883f7d3c0000(0000) >>> knlGS:0000000000000000 >>> [188995.245788] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 >>> [188995.245990] CR2: 00002b7092160fed CR3: 0000000977850000 CR4: >>> 00000000001406e0 >>> [188995.246388] Stack: >>> [188995.246581] 00002b92f71edfff.c 00002b7fffffffff.c 00002b92f71ee000.c >>> ffff8809778502b0.c >>> [188995.246981] 00002b763fffffff.c ffff8802e1895ec0.c ffffc90037283d48.c >>> ffff883f610a5b00.c >>> [188995.247365] ffffc90037283d70.c 00002b8000000000.c ffffc00000000fff.c >>> ffffea00879c3df0.c >>> [188995.247759] Call Trace: >>> [188995.247957] [<ffffffff811e26bd>] unmap_single_vma+0x7d/0xe0 >>> [188995.248161] [<ffffffff811e2a11>] unmap_vmas+0x51/0xa0 >>> [188995.248367] [<ffffffff811e98ed>] unmap_region+0xbd/0x130 >>> [188995.248571] [<ffffffff8170b04c>] ? >>> rwsem_down_write_failed_killable+0x31c/0x3f0 >>> [188995.248961] [<ffffffff811eb94c>] do_munmap+0x26c/0x420 >>> [188995.249162] [<ffffffff811ebbc0>] SyS_munmap+0x50/0x70 >>> [188995.249361] [<ffffffff8170cab7>] entry_SYSCALL_64_fastpath+0x1a/0xa9 >>> >>> By analyzing vmcore, khugepaged is waiting for vm-scalability process's >>> mmap_sem. >> >> OK, I see. >> >>> unmap_vmas will unmap every vma in the memory space, it sounds the test >>> generated huge amount of vmas. >> >> I would expect that it just takes some time to munmap 300G address >> range. >> >>> Shall we add "cond_resched()" in unmap_vmas(), i.e for every 100 vmas? It >>> may improve the responsiveness a little bit for non-preempt kernel, although >>> it still can't release the semaphore. >> >> We already do, once per pmd (see zap_pmd_range). > > It doesn't help. We would need to find a way to drop mmap_sem, if we're > holding it way too long. And doing it on per-vma count basis is not right > call. It won't address issue with single huge vma.
Yes, I agree. We have to find a way to release the semaphore at some point instead of holding it for the whole unmap.
> > Do we have any instrumentation that would help detect starvation on a > rw_semaphore?
ebpf might help?
Thanks, Yang
>
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