From: David Hildenbrand <david@redhat.com>
To: CGEL <cgel.zte@gmail.com>
Cc: bsingharora@gmail.com, akpm@linux-foundation.org,
yang.yang29@zte.com.cn, linux-kernel@vger.kernel.org,
linux-mm@kvack.org
Subject: Re: [PATCH] delayacct: track delays from ksm cow
Date: Thu, 17 Mar 2022 09:17:13 +0100 [thread overview]
Message-ID: <4e76476b-1da0-09c5-7dc4-0b2db796a549@redhat.com> (raw)
In-Reply-To: <6232970f.1c69fb81.4e365.c9f2@mx.google.com>
On 17.03.22 03:03, CGEL wrote:
> On Wed, Mar 16, 2022 at 03:56:23PM +0100, David Hildenbrand wrote:
>> On 16.03.22 14:34, cgel.zte@gmail.com wrote:
>>> From: Yang Yang <yang.yang29@zte.com.cn>
>>>
>>> Delay accounting does not track the delay of ksm cow. When tasks
>>> have many ksm pages, it may spend a amount of time waiting for ksm
>>> cow.
>>>
>>> To get the impact of tasks in ksm cow, measure the delay when ksm
>>> cow happens. This could help users to decide whether to user ksm
>>> or not.
>>>
>>> Also update tools/accounting/getdelays.c:
>>>
>>> / # ./getdelays -dl -p 231
>>> print delayacct stats ON
>>> listen forever
>>> PID 231
>>>
>>> CPU count real total virtual total delay total delay average
>>> 6247 1859000000 2154070021 1674255063 0.268ms
>>> IO count delay total delay average
>>> 0 0 0ms
>>> SWAP count delay total delay average
>>> 0 0 0ms
>>> RECLAIM count delay total delay average
>>> 0 0 0ms
>>> THRASHING count delay total delay average
>>> 0 0 0ms
>>> KSM count delay total delay average
>>> 3635 271567604 0ms
>>>
>>
>> TBH I'm not sure how particularly helpful this is and if we want this.
>>
> Thanks for replying.
>
> Users may use ksm by calling madvise(, , MADV_MERGEABLE) when they want
> save memory, it's a tradeoff by suffering delay on ksm cow. Users can
> get to know how much memory ksm saved by reading
> /sys/kernel/mm/ksm/pages_sharing, but they don't know what the costs of
> ksm cow delay, and this is important of some delay sensitive tasks. If
> users know both saved memory and ksm cow delay, they could better use
> madvise(, , MADV_MERGEABLE).
But that happens after the effects, no?
IOW a user already called madvise(, , MADV_MERGEABLE) and then gets the
results.
So how is this interface useful except for somebody writing an
application and simply being able to benchmark it with vs. without
MADV_MERGEABLE?
--
Thanks,
David / dhildenb
next prev parent reply other threads:[~2022-03-17 8:17 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-03-16 13:34 [PATCH] delayacct: track delays from ksm cow cgel.zte
2022-03-16 14:56 ` David Hildenbrand
2022-03-17 2:03 ` CGEL
2022-03-17 8:17 ` David Hildenbrand [this message]
2022-03-17 9:48 ` CGEL
2022-03-17 10:05 ` David Hildenbrand
2022-03-18 1:41 ` CGEL
2022-03-18 8:24 ` David Hildenbrand
2022-03-20 6:13 ` CGEL
2022-03-21 15:45 ` David Hildenbrand
2022-03-22 3:12 ` CGEL
2022-03-22 7:55 ` David Hildenbrand
2022-03-22 9:09 ` CGEL
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