From: Mike Kravetz <mike.kravetz@oracle.com>
To: Matthew Wilcox <willy@infradead.org>
Cc: David Rientjes <rientjes@google.com>,
linux-mm@kvack.org, linux-kernel@vger.kernel.org,
Song Liu <songliubraving@fb.com>,
"Kirill A.Shutemov" <kirill.shutemov@linux.intel.com>,
Mel Gorman <mgorman@techsingularity.net>,
Vlastimil Babka <vbabka@suse.cz>,
Andrew Morton <akpm@linux-foundation.org>
Subject: Re: [PATCH] mm: always consider THP when adjusting min_free_kbytes
Date: Thu, 6 Feb 2020 13:23:21 -0800 [thread overview]
Message-ID: <5e7800f2-3df3-a597-c164-5537b7f66417@oracle.com> (raw)
In-Reply-To: <20200206203945.GZ8731@bombadil.infradead.org>
On 2/6/20 12:39 PM, Matthew Wilcox wrote:
> On Wed, Feb 05, 2020 at 05:36:44PM -0800, Mike Kravetz wrote:
>> The value of min_free_kbytes is calculated in two routines:
>> 1) init_per_zone_wmark_min based on available memory
>> 2) set_recommended_min_free_kbytes may reserve extra space for
>> THP allocations
>>
>> In both of these routines, a user defined min_free_kbytes value will
>> be overwritten if the value calculated in the code is larger. No message
>> is logged if the user value is overwritten.
>>
>> Change code to never overwrite user defined value. However, do log a
>> message (once per value) showing the value calculated in code.
>
> But what if the user set min_free_kbytes to, say, half of system memory,
> and then hot-unplugs three quarters of their memory? I think the kernel
> should protect itself against such foolishness.
I'm not sure what we should set it to in this case. Previously you said,
>> I'm reluctant to suggest we do a more complex adjustment of the value
>> (eg figure out what the adjustment would have been, then apply some
>> fraction of that adjustment to keep the ratios in proportion) because
>> we don't really know why they adjusted it.
So, I suspect you would suggest setting it to the default computed value?
But then, when do we start adjusting? What if they only remove a small
amount of memory? And, then add the same amount back in?
BTW - In the above scenario existing code would not change min_free_kbytes
because the user defined value is greater than value computed in code.
--
Mike Kravetz
next prev parent reply other threads:[~2020-02-06 21:23 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-02-04 19:41 [PATCH] mm: always consider THP when adjusting min_free_kbytes Mike Kravetz
2020-02-04 20:33 ` David Rientjes
2020-02-04 21:42 ` Mike Kravetz
2020-02-04 21:53 ` Matthew Wilcox
2020-02-05 0:33 ` Mike Kravetz
2020-02-06 1:36 ` Mike Kravetz
2020-02-06 20:09 ` Khalid Aziz
2020-02-06 20:39 ` Matthew Wilcox
2020-02-06 21:23 ` Mike Kravetz [this message]
2020-02-06 21:32 ` Matthew Wilcox
2020-02-10 18:58 ` Mike Kravetz
2020-02-04 23:37 ` Khalid Aziz
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