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From: Vijay Balakrishna <vijayb@linux.microsoft.com>
To: Pavel Tatashin <pasha.tatashin@soleen.com>,
	"Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
	Oleg Nesterov <oleg@redhat.com>, Song Liu <songliubraving@fb.com>,
	Andrea Arcangeli <aarcange@redhat.com>,
	Allen Pais <apais@microsoft.com>,
	LKML <linux-kernel@vger.kernel.org>,
	linux-mm <linux-mm@kvack.org>
Subject: Re: [[PATCH]] mm: khugepaged: recalculate min_free_kbytes after memory hotplug as expected by khugepaged
Date: Thu, 10 Sep 2020 15:56:57 -0700	[thread overview]
Message-ID: <a153dae8-77c2-f298-0ae5-9956560f9382@linux.microsoft.com> (raw)
In-Reply-To: <CA+CK2bACLNVqKP9Mgr37HQKOY=7+-PwuLCtqN6+saW7uuiMCfw@mail.gmail.com>



On 9/10/2020 3:28 PM, Pavel Tatashin wrote:
> Hi Kirill,
> 
> On Thu, Sep 10, 2020 at 6:01 PM Kirill A. Shutemov
> <kirill.shutemov@linux.intel.com> wrote:
>>
>> On Thu, Sep 10, 2020 at 01:47:39PM -0700, Vijay Balakrishna wrote:
>>> When memory is hotplug added or removed the min_free_kbytes must be
>>> recalculated based on what is expected by khugepaged.  Currently
>>> after hotplug, min_free_kbytes will be set to a lower default and higher
>>> default set when THP enabled is lost. This leaves the system with small
>>> min_free_kbytes which isn't suitable for systems especially with network
>>> intensive loads.  Typical failure symptoms include HW WATCHDOG reset,
>>> soft lockup hang notices, NETDEVICE WATCHDOG timeouts, and OOM process
>>> kills.
>>>
>>> Fixes: f000565adb77 ("thp: set recommended min free kbytes")
>>>
>>> Signed-off-by: Vijay Balakrishna <vijayb@linux.microsoft.com>
>>> Cc: stable@vger.kernel.org
>>
>> NAK. It would override min_free_kbytes set by user.
> 
> Hi Kirill,
> 
> Thank you for looking into this. How is this different from when
> khugepaged modifies it?
> 
> echo always >/sys/kernel/mm/transparent_hugepage/enabled
> 
> Which results in:
> 
> start_stop_khugepaged
>    set_recommended_min_free_kbytes
> 
> Which will also adjust min_free_kbytes according to hugepaged requirement?
> 
> This bug that Vijay described is another hot-plug related issue that
> we have found on our system where we perform memory hot add and hot
> remove on every reboot.
> 
> Thank you,
> Pasha
> 

Thanks Kirill for taking a look and spotting it.

IIUC, it is an existing issue, we should fix it while we are at it. 
Otherwise with my propsed patch introduces a regression for hotplug 
memory consumers with THP enabled and min_free_kbytes set by user higher 
than calculated by THP.

Vijay

  reply	other threads:[~2020-09-10 22:57 UTC|newest]

Thread overview: 17+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-09-10 20:47 [[PATCH]] mm: khugepaged: recalculate min_free_kbytes after memory hotplug as expected by khugepaged Vijay Balakrishna
2020-09-10 22:01 ` Kirill A. Shutemov
2020-09-10 22:28   ` Pavel Tatashin
2020-09-10 22:56     ` Vijay Balakrishna [this message]
2020-09-15  5:04   ` Vijay Balakrishna
2020-09-14 14:33 ` Michal Hocko
2020-09-14 16:57   ` Vijay Balakrishna
2020-09-15  8:18     ` Michal Hocko
2020-09-15 15:48       ` Vijay Balakrishna
2020-09-16  6:53         ` Michal Hocko
2020-09-16 18:28           ` Vijay Balakrishna
2020-09-17 12:12             ` Michal Hocko
2020-09-17 18:03               ` Vijay Balakrishna
2020-09-18  5:45                 ` Michal Hocko
2020-09-18 15:32                   ` Vijay Balakrishna
2020-09-21  7:00                     ` Michal Hocko
2020-09-15 18:22 ` Pavel Tatashin

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