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From: Andrew Morton <>
To: Yang Shi <>
	David Rientjes <>
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 13:41:39 -0800	[thread overview]
Message-ID: <> (raw)
In-Reply-To: <>

On Tue, 6 Mar 2018 13:17:37 -0800 Yang Shi <> 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.


> >
> > 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 ( 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?

  reply	other threads:[~2018-03-06 21:41 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 [this message]
2018-03-07  0:47       ` Yang Shi

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