From: Rik van Riel <riel@surriel.com>
To: Andrew Morton <akpm@linux-foundation.org>,
Kelley Nielsen <kelleynnn@gmail.com>
Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org,
opw-kernel@googlegroups.com, jamieliu@google.com,
sjenning@linux.vnet.ibm.com, Hugh Dickins <hughd@google.com>
Subject: Re: [RFC] mm:prototype for the updated swapoff implementation
Date: Wed, 19 Feb 2014 16:39:47 -0500 [thread overview]
Message-ID: <530524A3.6090700@surriel.com> (raw)
In-Reply-To: <20140219132757.58b61f07bad914b3848275e9@linux-foundation.org>
On 02/19/2014 04:27 PM, Andrew Morton wrote:
> On Tue, 18 Feb 2014 16:35:22 -0800 Kelley Nielsen <kelleynnn@gmail.com> wrote:
>
>> The function try_to_unuse() is of quadratic complexity, with a lot of
>> wasted effort. It unuses swap entries one by one, potentially iterating
>> over all the page tables for all the processes in the system for each
>> one.
>>
>> This new proposed implementation of try_to_unuse simplifies its
>> complexity to linear. It iterates over the system's mms once, unusing
>> all the affected entries as it walks each set of page tables. It also
>> makes similar changes to shmem_unuse.
>>
>> Improvement
>>
>> swapoff was called on a swap partition containing about 50M of data,
>> and calls to the function unuse_pte_range were counted.
>>
>> Present implementation....about 22.5M calls.
>> Prototype.................about 7.0K calls.
>
> Do you have situations in which swapoff is taking an unacceptable
> amount of time? If so, please update the changelog to provide full
> details on this, with before-and-after timing measurements.
I have seen plenty of that. With just a few GB in swap space in
use, on a system with 24GB of RAM, and about a dozen GB in use
by various processes, I have seen swapoff take several hours of
CPU time.
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next prev parent reply other threads:[~2014-02-19 21:39 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-02-19 0:35 Kelley Nielsen
2014-02-19 21:27 ` Andrew Morton
2014-02-19 21:39 ` Rik van Riel [this message]
2014-02-19 23:08 ` [OPW kernel] " Josh Triplett
2014-02-19 23:42 ` One Thousand Gnomes
2014-02-25 20:14 ` Rik van Riel
2014-02-28 0:33 ` Hugh Dickins
2014-02-28 18:07 ` Rik van Riel
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