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From: Yang Shi <yang.shi@linux.alibaba.com>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: mingo@kernel.org, adobriyan@gmail.com, linux-mm@kvack.org,
	linux-kernel@vger.kernel.org,
	David Rientjes <rientjes@google.com>
Subject: Re: [RFC PATCH 0/4 v2] Define killable version for access_remote_vm() and use it in fs/proc
Date: Tue, 6 Mar 2018 16:47:22 -0800	[thread overview]
Message-ID: <ae008700-3bf6-ed96-865e-5a60694db7c8@linux.alibaba.com> (raw)
In-Reply-To: <20180306134139.375e15abab173329962f7d5a@linux-foundation.org>



On 3/6/18 1:41 PM, Andrew Morton wrote:
> On Tue, 6 Mar 2018 13:17:37 -0800 Yang Shi <yang.shi@linux.alibaba.com> wrote:
>
>>
>> It just mitigates the hung task warning, can't resolve the mmap_sem
>> scalability issue. Furthermore, waiting on pure uninterruptible state
>> for reading /proc sounds unnecessary. It doesn't wait for I/O completion.
> OK.

Since we already had down_read_killable() APIs available, IMHO, giving 
application a chance to abort at some circumstances sounds not bad.

>
>>> Where the heck are we holding mmap_sem for so long?  Can that be fixed?
>> The mmap_sem is held for unmapping a large map which has every single
>> page mapped. This is not a issue in real production code. Just found it
>> by running vm-scalability on a machine with ~600GB memory.
>>
>> AFAIK, I don't see any easy fix for the mmap_sem scalability issue. I
>> saw range locking patches (https://lwn.net/Articles/723648/) were
>> floating around. But, it may not help too much on the case that a large
>> map with every single page mapped.
> Well it sounds fairly simple to mitigate?  Simplistically: don't unmap
> 600G in a single hit; do it 1G at a time, dropping mmap_sem each time.
> A smarter version might only come up for air if there are mmap_sem
> waiters and if it has already done some work.  I don't think we have
> any particular atomicity requirements when unmapping?

I'm not quite sure. But, the existing applications may assume munmap is 
atomic?

Thanks,
Yang

>

      reply	other threads:[~2018-03-07  0:47 UTC|newest]

Thread overview: 16+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-02-27  0:25 [RFC PATCH 0/4 v2] Define killable version for access_remote_vm() and use it in fs/proc Yang Shi
2018-02-27  0:25 ` [PATCH 1/4 v2] mm: add access_remote_vm_killable APIs Yang Shi
2018-02-27  0:25 ` [PATCH 2/4 v2] fs: proc: use down_read_killable in proc_pid_cmdline_read() Yang Shi
2018-02-27  0:25 ` [PATCH 3/4 v2] fs: proc: use down_read_killable() in environ_read() Yang Shi
2018-02-27  7:15   ` Alexey Dobriyan
2018-02-27 16:59     ` Yang Shi
2018-02-27  0:25 ` [PATCH 4/4 v2] mm: use access_remote_vm() in get_cmdline() Yang Shi
2018-02-27  1:02 ` [RFC PATCH 0/4 v2] Define killable version for access_remote_vm() and use it in fs/proc David Rientjes
2018-02-27  1:25   ` Yang Shi
2018-02-27  1:47     ` David Rientjes
2018-03-01  0:17       ` Yang Shi
2018-03-06 18:45 ` Yang Shi
2018-03-06 20:45 ` Andrew Morton
2018-03-06 21:17   ` Yang Shi
2018-03-06 21:41     ` Andrew Morton
2018-03-07  0:47       ` Yang Shi [this message]

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