From: Pavel Emelyanov <xemul@parallels.com>
To: Matt Mackall <mpm@selenic.com>,
Andrew Morton <akpm@linux-foundation.org>
Cc: Hugh Dickins <hughd@google.com>,
KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>,
Michal Hocko <mhocko@suse.cz>, Mel Gorman <mgorman@suse.de>,
Johannes Weiner <hannes@cmpxchg.org>,
Linux MM <linux-mm@kvack.org>, Rik van Riel <riel@redhat.com>,
Wu Fengguang <fengguang.wu@intel.com>
Subject: Re: [RFC PATCH 0/2] mm: Add ability to monitor task's memory changes
Date: Wed, 05 Dec 2012 13:53:17 +0400 [thread overview]
Message-ID: <50BF198D.3030509@parallels.com> (raw)
In-Reply-To: <1354667937.6733.233.camel@calx>
On 12/05/2012 04:38 AM, Matt Mackall wrote:
> On Tue, 2012-12-04 at 16:24 -0800, Andrew Morton wrote:
>> On Tue, 04 Dec 2012 18:17:08 -0600
>> Matt Mackall <mpm@selenic.com> wrote:
>>
>>> On Tue, 2012-12-04 at 15:21 -0800, Andrew Morton wrote:
>>>> On Tue, 04 Dec 2012 09:15:10 +0400
>>>> Pavel Emelyanov <xemul@parallels.com> wrote:
>>>>
>>>>>
>>>>>> Two alternatives come to mind:
>>>>>>
>>>>>> 1) Use /proc/pid/pagemap (Documentation/vm/pagemap.txt) in some
>>>>>> fashion to determine which pages have been touched.
>>>
>>> [momentarily coming out of kernel retirement for old man rant]
>>>
>>> This is a popular interface anti-pattern.
>>>
>>> You shouldn't use an interface that gives you huge amount of STATE to
>>> detect small amounts of CHANGE via manual differentiation.
>>
>> I'm not sure that's what checkpoint-restart will be doing. If we want
>> to determine "which pages have been touched since the last checkpoint
>> ten minutes ago" then that set of touched pages *is* state. And it's
>> not "small"!
>
> Yeah, there is definitely a middle-ground here between "I want
> high-frequency updates" and "I want to see the whole picture".
> The filesystem analogy is backups: we don't have any good way to say
> "find me all files changed since yesterday" short of "find all files".
> The closest thing is explicit snapshotting.
For what is required for checkpoint-restore is -- we want to query the kernel
for "what pages has been written to since moment X". But this "moment X" is
a little bit more tricky than just "mark all pages r/o". Consider we're doing
this periodically. So when defining the moment X for the 2nd time we should
query the "changed" state and remap the respective page r/o atomically. Full
snapshot is actually not required, since we don't need to keep the old copy
of a page that is written to. Just a sign, that this page was modified is OK.
Thanks,
Pavel
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next prev parent reply other threads:[~2012-12-05 9:54 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-11-30 17:55 Pavel Emelyanov
2012-11-30 17:55 ` [PATCH 1/2] mm: Mark VMA with VM_TRACE bit Pavel Emelyanov
2012-11-30 17:55 ` [PATCH 2/2] mm: Generate events when tasks change their memory Pavel Emelyanov
2012-12-03 23:42 ` Xiao Guangrong
2012-12-04 5:04 ` Pavel Emelyanov
2012-12-03 8:36 ` [RFC PATCH 0/2] mm: Add ability to monitor task's memory changes Glauber Costa
2012-12-03 20:16 ` Marcelo Tosatti
2012-12-04 7:39 ` Glauber Costa
2012-12-03 22:43 ` Andrew Morton
2012-12-04 5:15 ` Pavel Emelyanov
2012-12-04 23:21 ` Andrew Morton
2012-12-05 0:17 ` Matt Mackall
2012-12-05 0:24 ` Andrew Morton
2012-12-05 0:38 ` Matt Mackall
2012-12-05 9:53 ` Pavel Emelyanov [this message]
2012-12-05 22:06 ` Andrew Morton
2012-12-06 6:32 ` Pavel Emelyanov
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