From: Hugh Dickins <hughd@google.com>
To: Simon Jeons <simon.jeons@gmail.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
Petr Holasek <pholasek@redhat.com>,
Andrea Arcangeli <aarcange@redhat.com>,
Izik Eidus <izik.eidus@ravellosystems.com>,
Gerald Schaefer <gerald.schaefer@de.ibm.com>,
KOSAKI Motohiro <kosaki.motohiro@gmail.com>,
linux-kernel@vger.kernel.org, linux-mm@kvack.org
Subject: Re: [PATCH 11/11] ksm: stop hotremove lockdep warning
Date: Sun, 27 Jan 2013 15:35:21 -0800 (PST) [thread overview]
Message-ID: <alpine.LNX.2.00.1301271526040.17495@eggly.anvils> (raw)
In-Reply-To: <1359267810.6763.1.camel@kernel>
On Sun, 27 Jan 2013, Simon Jeons wrote:
> On Fri, 2013-01-25 at 18:10 -0800, Hugh Dickins wrote:
> > @@ -2098,15 +2117,15 @@ static int ksm_memory_callback(struct no
> > switch (action) {
> > case MEM_GOING_OFFLINE:
> > /*
> > - * Keep it very simple for now: just lock out ksmd and
> > - * MADV_UNMERGEABLE while any memory is going offline.
> > - * mutex_lock_nested() is necessary because lockdep was alarmed
> > - * that here we take ksm_thread_mutex inside notifier chain
> > - * mutex, and later take notifier chain mutex inside
> > - * ksm_thread_mutex to unlock it. But that's safe because both
> > - * are inside mem_hotplug_mutex.
> > + * Prevent ksm_do_scan(), unmerge_and_remove_all_rmap_items()
> > + * and remove_all_stable_nodes() while memory is going offline:
> > + * it is unsafe for them to touch the stable tree at this time.
> > + * But unmerge_ksm_pages(), rmap lookups and other entry points
>
> Why unmerge_ksm_pages beneath us is safe for ksm memory hotremove?
>
> > + * which do not need the ksm_thread_mutex are all safe.
It's just like userspace doing a write-fault on every KSM page in the vma.
If that were unsafe for memory hotremove, then it would not be KSM's
problem, memory hotremove would already be unsafe. (But memory hotremove
is safe because it migrates away from all the pages to be removed before
it can reach MEM_OFFLINE.)
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next prev parent reply other threads:[~2013-01-27 23:35 UTC|newest]
Thread overview: 69+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-01-26 1:53 [PATCH 0/11] ksm: NUMA trees and page migration Hugh Dickins
2013-01-26 1:54 ` [PATCH 1/11] ksm: allow trees per NUMA node Hugh Dickins
2013-01-27 1:14 ` Simon Jeons
2013-01-27 2:54 ` Hugh Dickins
2013-01-27 3:16 ` Simon Jeons
2013-01-27 21:55 ` Hugh Dickins
2013-01-28 23:03 ` Andrew Morton
2013-01-29 1:17 ` Hugh Dickins
2013-01-28 23:08 ` Andrew Morton
2013-01-29 1:38 ` Hugh Dickins
2013-02-05 16:41 ` Mel Gorman
2013-02-07 23:57 ` Hugh Dickins
2013-01-26 1:56 ` [PATCH 2/11] ksm: add sysfs ABI Documentation Hugh Dickins
2013-01-26 1:58 ` [PATCH 3/11] ksm: trivial tidyups Hugh Dickins
2013-01-28 23:11 ` Andrew Morton
2013-01-29 1:44 ` Hugh Dickins
2013-01-26 1:59 ` [PATCH 4/11] ksm: reorganize ksm_check_stable_tree Hugh Dickins
2013-02-05 16:48 ` Mel Gorman
2013-02-08 0:07 ` Hugh Dickins
2013-02-14 11:30 ` Mel Gorman
2013-01-26 2:00 ` [PATCH 5/11] ksm: get_ksm_page locked Hugh Dickins
2013-01-27 2:36 ` Simon Jeons
2013-01-27 22:08 ` Hugh Dickins
2013-01-28 0:36 ` Simon Jeons
2013-01-28 3:35 ` Hugh Dickins
2013-01-27 2:48 ` Simon Jeons
2013-01-27 22:10 ` Hugh Dickins
2013-02-05 17:18 ` Mel Gorman
2013-02-08 0:33 ` Hugh Dickins
2013-02-14 11:34 ` Mel Gorman
2013-01-26 2:01 ` [PATCH 6/11] ksm: remove old stable nodes more thoroughly Hugh Dickins
2013-01-27 4:55 ` Simon Jeons
2013-01-27 23:05 ` Hugh Dickins
2013-01-28 1:42 ` Simon Jeons
2013-01-28 4:14 ` Hugh Dickins
2013-01-28 2:12 ` Simon Jeons
2013-01-28 4:19 ` Hugh Dickins
2013-01-28 6:36 ` Simon Jeons
2013-01-28 23:44 ` Andrew Morton
2013-01-29 2:03 ` Hugh Dickins
2013-02-05 17:55 ` Mel Gorman
2013-02-08 19:33 ` Hugh Dickins
2013-02-14 11:58 ` Mel Gorman
2013-02-14 22:19 ` Hugh Dickins
2013-01-26 2:03 ` [PATCH 7/11] ksm: make KSM page migration possible Hugh Dickins
2013-01-27 5:47 ` Simon Jeons
2013-01-27 23:12 ` Hugh Dickins
2013-01-28 0:41 ` Simon Jeons
2013-01-28 3:44 ` Hugh Dickins
2013-02-05 19:11 ` Mel Gorman
2013-02-08 20:52 ` Hugh Dickins
2013-01-26 2:05 ` [PATCH 8/11] ksm: make !merge_across_nodes migration safe Hugh Dickins
2013-01-27 8:49 ` Simon Jeons
2013-01-27 23:25 ` Hugh Dickins
2013-01-28 3:44 ` Simon Jeons
2013-01-26 2:06 ` [PATCH 9/11] ksm: enable KSM page migration Hugh Dickins
2013-01-26 2:07 ` [PATCH 10/11] mm: remove offlining arg to migrate_pages Hugh Dickins
2013-01-26 2:10 ` [PATCH 11/11] ksm: stop hotremove lockdep warning Hugh Dickins
2013-01-27 6:23 ` Simon Jeons
2013-01-27 23:35 ` Hugh Dickins [this message]
2013-02-08 18:45 ` Gerald Schaefer
2013-02-11 22:13 ` Hugh Dickins
2013-01-28 23:54 ` [PATCH 0/11] ksm: NUMA trees and page migration Andrew Morton
2013-01-29 0:49 ` Izik Eidus
2013-01-29 2:26 ` Izik Eidus
2013-01-29 16:51 ` Andrea Arcangeli
2013-01-31 0:05 ` Ric Mason
2013-01-29 1:07 ` Hugh Dickins
2013-01-29 10:45 ` Gleb Natapov
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