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From: Vlastimil Babka <vbabka@suse.cz>
To: Michal Hocko <mhocko@kernel.org>
Cc: Anshuman Khandual <khandual@linux.vnet.ibm.com>,
	linux-mm@kvack.org, linux-kernel@vger.kernel.org,
	akpm@linux-foundation.org, mike.kravetz@oracle.com
Subject: Re: [RFC] mm/mremap: Remove redundant checks inside vma_expandable()
Date: Tue, 11 Jul 2017 08:56:04 +0200	[thread overview]
Message-ID: <337a8a4c-1f27-7371-409d-6a9f181b3871@suse.cz> (raw)
In-Reply-To: <20170711065030.GE24852@dhcp22.suse.cz>

On 07/11/2017 08:50 AM, Michal Hocko wrote:
> On Tue 11-07-17 08:26:40, Vlastimil Babka wrote:
>> On 07/11/2017 08:03 AM, Michal Hocko wrote:
>>>
>>> Are you telling me that two if conditions cause more than a second
>>> difference? That sounds suspicious.
>>
>> It's removing also a call to get_unmapped_area(), AFAICS. That means a
>> vma search?
> 
> Ohh, right. I have somehow missed that. Is this removal intentional?

I think it is: "Checking for availability of virtual address range at
the end of the VMA for the incremental size is also reduntant at this
point."

> The
> changelog is silent about it.

It doesn't explain why it's redundant, indeed. Unfortunately, the commit
f106af4e90ea ("fix checks for expand-in-place mremap") which added this,
also doesn't explain why it's needed.

WARNING: multiple messages have this Message-ID (diff)
From: Vlastimil Babka <vbabka@suse.cz>
To: Michal Hocko <mhocko@kernel.org>
Cc: Anshuman Khandual <khandual@linux.vnet.ibm.com>,
	linux-mm@kvack.org, linux-kernel@vger.kernel.org,
	akpm@linux-foundation.org, mike.kravetz@oracle.com
Subject: Re: [RFC] mm/mremap: Remove redundant checks inside vma_expandable()
Date: Tue, 11 Jul 2017 08:56:04 +0200	[thread overview]
Message-ID: <337a8a4c-1f27-7371-409d-6a9f181b3871@suse.cz> (raw)
In-Reply-To: <20170711065030.GE24852@dhcp22.suse.cz>

On 07/11/2017 08:50 AM, Michal Hocko wrote:
> On Tue 11-07-17 08:26:40, Vlastimil Babka wrote:
>> On 07/11/2017 08:03 AM, Michal Hocko wrote:
>>>
>>> Are you telling me that two if conditions cause more than a second
>>> difference? That sounds suspicious.
>>
>> It's removing also a call to get_unmapped_area(), AFAICS. That means a
>> vma search?
> 
> Ohh, right. I have somehow missed that. Is this removal intentional?

I think it is: "Checking for availability of virtual address range at
the end of the VMA for the incremental size is also reduntant at this
point."

> The
> changelog is silent about it.

It doesn't explain why it's redundant, indeed. Unfortunately, the commit
f106af4e90ea ("fix checks for expand-in-place mremap") which added this,
also doesn't explain why it's needed.

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  reply	other threads:[~2017-07-11  6:56 UTC|newest]

Thread overview: 34+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-07-10 11:10 [RFC] mm/mremap: Remove redundant checks inside vma_expandable() Anshuman Khandual
2017-07-10 11:10 ` Anshuman Khandual
2017-07-10 13:49 ` Michal Hocko
2017-07-10 13:49   ` Michal Hocko
2017-07-11  4:28   ` Anshuman Khandual
2017-07-11  4:28     ` Anshuman Khandual
2017-07-11  6:03     ` Michal Hocko
2017-07-11  6:03       ` Michal Hocko
2017-07-11  6:26       ` Vlastimil Babka
2017-07-11  6:26         ` Vlastimil Babka
2017-07-11  6:50         ` Michal Hocko
2017-07-11  6:50           ` Michal Hocko
2017-07-11  6:56           ` Vlastimil Babka [this message]
2017-07-11  6:56             ` Vlastimil Babka
2017-07-11  7:16             ` Michal Hocko
2017-07-11  7:16               ` Michal Hocko
2017-07-11  7:22               ` Michal Hocko
2017-07-11  7:22                 ` Michal Hocko
2017-07-11 11:19                 ` Anshuman Khandual
2017-07-11 11:19                   ` Anshuman Khandual
2017-07-11 11:11               ` Anshuman Khandual
2017-07-11 11:11                 ` Anshuman Khandual
2017-07-11 11:08             ` Anshuman Khandual
2017-07-11 11:08               ` Anshuman Khandual
2017-07-11 11:22               ` Michal Hocko
2017-07-11 11:22                 ` Michal Hocko
2017-07-19  6:49                 ` Anshuman Khandual
2017-07-19  6:49                   ` Anshuman Khandual
2017-07-11 11:06           ` Anshuman Khandual
2017-07-11 11:06             ` Anshuman Khandual
2017-07-11  9:44         ` Anshuman Khandual
2017-07-11  9:44           ` Anshuman Khandual
2017-07-11  4:29   ` Anshuman Khandual
2017-07-11  4:29     ` Anshuman Khandual

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