From: "Raslan, KarimAllah" <karahmed@amazon.de>
To: Dan Williams <dan.j.williams@intel.com>
Cc: Michal Hocko <mhocko@kernel.org>,
"linux-mm@kvack.org" <linux-mm@kvack.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
Andrew Morton <akpm@linux-foundation.org>,
Mel Gorman <mgorman@techsingularity.net>,
Vlastimil Babka <vbabka@suse.cz>,
Johannes Weiner <hannes@cmpxchg.org>,
Yaowei Bai <baiyaowei@cmss.chinamobile.com>,
Joe Perches <joe@perches.com>, Tejun Heo <tj@kernel.org>,
"Liguori, Anthony" <aliguori@amazon.com>,
"Schoenherr, Jan H." <jschoenh@amazon.de>
Subject: Re: [PATCH] sparse: Track the boundaries of memory sections for accurate checks
Date: Wed, 14 Sep 2016 22:11:00 +0000 [thread overview]
Message-ID: <7D63A80D-53B7-460A-A74D-0005B7D499D6@amazon.de> (raw)
In-Reply-To: <CAPcyv4gQZ-=6SdsGc-YafcAUz0WWxtGuh56CPan1xqSkWbd9=A@mail.gmail.com>
Ahmed, Karim Allah
karahmed@amazon.de
> On Sep 15, 2016, at 12:05 AM, Dan Williams <dan.j.williams@intel.com> wrote:
>
> On Wed, Sep 14, 2016 at 2:40 PM, Raslan, KarimAllah <karahmed@amazon.de> wrote:
>>
>>
>> On 6/20/16, 10:23 AM, "Michal Hocko" <mhocko@kernel.org> wrote:
>>
>> On Sat 18-06-16 12:11:19, KarimAllah Ahmed wrote:
>>> When sparse memory model is used an array of memory sections is created to
>>> track each block of contiguous physical pages. Each element of this array
>>> contains PAGES_PER_SECTION pages. During the creation of this array the actual
>>> boundaries of the memory block is lost, so the whole block is either considered
>>> as present or not.
>>>
>>> pfn_valid() in the sparse memory configuration checks which memory sections the
>>> pfn belongs to then checks whether it's present or not. This yields sub-optimal
>>> results when the available memory doesn't cover the whole memory section,
>>> because pfn_valid will return 'true' even for the unavailable pfns at the
>>> boundaries of the memory section.
>>
>> Please be more verbose of _why_ the patch is needed. Why those
>> "sub-optimal results" matter?
>>
>> Does this make sense to you ?
>
> [ channeling my inner akpm ]
>
> What's the user visible effect of this change? What code is getting
> tripped up by pfn_valid() being imprecise, and why is changing
> pfn_valid() the preferred fix?
I did expand the commit message in v2 of this patch to answer these questions:
https://patchwork.kernel.org/patch/9190737/
Amazon Development Center Germany GmbH
Berlin - Dresden - Aachen
main office: Krausenstr. 38, 10117 Berlin
Geschaeftsfuehrer: Dr. Ralf Herbrich, Christian Schlaeger
Ust-ID: DE289237879
Eingetragen am Amtsgericht Charlottenburg HRB 149173 B
next prev parent reply other threads:[~2016-09-14 22:11 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-06-18 10:11 [PATCH] sparse: Track the boundaries of memory sections for accurate checks KarimAllah Ahmed
2016-06-20 8:23 ` Michal Hocko
2016-06-21 14:33 ` [PATCH v2] " KarimAllah Ahmed
2016-09-14 21:40 ` [PATCH] " Raslan, KarimAllah
2016-09-14 22:05 ` Dan Williams
2016-09-14 22:11 ` Raslan, KarimAllah [this message]
2016-09-14 22:53 ` Dan Williams
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