From: Andrew Morton <akpm@linux-foundation.org>
To: Pavel Emelyanov <xemul@parallels.com>
Cc: Matt Mackall <mpm@selenic.com>, 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, 5 Dec 2012 14:06:02 -0800 [thread overview]
Message-ID: <20121205140602.1d8340a8.akpm@linux-foundation.org> (raw)
In-Reply-To: <50BF198D.3030509@parallels.com>
On Wed, 05 Dec 2012 13:53:17 +0400
Pavel Emelyanov <xemul@parallels.com> wrote:
> 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.
How is all this going to work, btw? What is the interface to query
page states and set them read-only? How will dirty pagecache and dirty
swapcache be handled? And anonymous memory?
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next prev parent reply other threads:[~2012-12-05 22:06 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-11-30 17:55 [RFC PATCH 0/2] mm: Add ability to monitor task's memory changes 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
2012-12-05 22:06 ` Andrew Morton [this message]
2012-12-06 6:32 ` Pavel Emelyanov
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