From: Oscar Salvador <osalvador@techadventures.net>
To: Michal Hocko <mhocko@kernel.org>
Cc: Alexander Duyck <alexander.h.duyck@linux.intel.com>,
linux-mm@kvack.org, akpm@linux-foundation.org,
linux-kernel@vger.kernel.org, linux-nvdimm@lists.01.org,
pavel.tatashin@microsoft.com, dave.jiang@intel.com,
dave.hansen@intel.com, jglisse@redhat.com,
rppt@linux.vnet.ibm.com, dan.j.williams@intel.com,
logang@deltatee.com, mingo@kernel.org,
kirill.shutemov@linux.intel.com
Subject: Re: [PATCH v5 4/4] mm: Defer ZONE_DEVICE page initialization to the point where we init pgmap
Date: Fri, 28 Sep 2018 10:12:24 +0200 [thread overview]
Message-ID: <20180928081224.GA25561@techadventures.net> (raw)
In-Reply-To: <20180927131329.GI6278@dhcp22.suse.cz>
On Thu, Sep 27, 2018 at 03:13:29PM +0200, Michal Hocko wrote:
> I would have to double check but is the hotplug lock really serializing
> access to the state initialized by init_currently_empty_zone? E.g.
> zone_start_pfn is a nice example of a state that is used outside of the
> lock. zone's free lists are similar. So do we really need the hoptlug
> lock? And more broadly, what does the hotplug lock is supposed to
> serialize in general. A proper documentation would surely help to answer
> these questions. There is way too much of "do not touch this code and
> just make my particular hack" mindset which made the whole memory
> hotplug a giant pile of mess. We really should start with some proper
> engineering here finally.
* Locking rules:
*
* zone_start_pfn and spanned_pages are protected by span_seqlock.
* It is a seqlock because it has to be read outside of zone->lock,
* and it is done in the main allocator path. But, it is written
* quite infrequently.
*
* Write access to present_pages at runtime should be protected by
* mem_hotplug_begin/end(). Any reader who can't tolerant drift of
* present_pages should get_online_mems() to get a stable value.
IIUC, looks like zone_start_pfn should be envolved with
zone_span_writelock/zone_span_writeunlock, and since zone_start_pfn is changed
in init_currently_empty_zone, I guess that the whole function should be within
that lock.
So, a blind shot, but could we do something like the following?
diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
index 898e1f816821..49f87252f1b1 100644
--- a/mm/memory_hotplug.c
+++ b/mm/memory_hotplug.c
@@ -764,14 +764,13 @@ void __ref move_pfn_range_to_zone(struct zone *zone, unsigned long start_pfn,
int nid = pgdat->node_id;
unsigned long flags;
- if (zone_is_empty(zone))
- init_currently_empty_zone(zone, start_pfn, nr_pages);
-
clear_zone_contiguous(zone);
/* TODO Huh pgdat is irqsave while zone is not. It used to be like that before */
pgdat_resize_lock(pgdat, &flags);
zone_span_writelock(zone);
+ if (zone_is_empty(zone))
+ init_currently_empty_zone(zone, start_pfn, nr_pages);
resize_zone_range(zone, start_pfn, nr_pages);
zone_span_writeunlock(zone);
resize_pgdat_range(pgdat, start_pfn, nr_pages);
Then, we could take move_pfn_range_to_zone out of the hotplug lock.
Although I am not sure about leaving memmap_init_zone unprotected.
For the normal memory, that is not a problem since the memblock's lock
protects us from touching the same pages at the same time in online/offline_pages,
but for HMM/devm the story is different.
I am totally unaware of HMM/devm, so I am not sure if its protected somehow.
e.g: what happens if devm_memremap_pages and devm_memremap_pages_release are running
at the same time for the same memory-range (with the assumption that the hotplug-lock
does not protect move_pfn_range_to_zone anymore).
--
Oscar Salvador
SUSE L3
next prev parent reply other threads:[~2018-09-28 8:12 UTC|newest]
Thread overview: 77+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-09-25 20:18 [PATCH v5 0/4] Address issues slowing persistent memory initialization Alexander Duyck
2018-09-25 20:19 ` [PATCH v5 1/4] mm: Remove now defunct NO_BOOTMEM from depends list for deferred init Alexander Duyck
2018-09-25 21:05 ` Mike Rapoport
2018-09-25 20:20 ` [PATCH v5 2/4] mm: Provide kernel parameter to allow disabling page init poisoning Alexander Duyck
2018-09-25 20:26 ` Dave Hansen
2018-09-25 20:38 ` Alexander Duyck
2018-09-25 22:14 ` Dave Hansen
2018-09-25 22:27 ` Alexander Duyck
2018-09-26 7:38 ` Michal Hocko
2018-09-26 15:24 ` Alexander Duyck
2018-09-26 15:39 ` Michal Hocko
2018-09-26 15:41 ` Dave Hansen
2018-09-26 16:18 ` Alexander Duyck
2018-09-26 15:36 ` Dave Hansen
2018-09-26 22:36 ` Andrew Morton
2018-09-25 20:20 ` [PATCH v5 3/4] mm: Create non-atomic version of SetPageReserved for init use Alexander Duyck
2018-09-25 20:21 ` [PATCH v5 4/4] mm: Defer ZONE_DEVICE page initialization to the point where we init pgmap Alexander Duyck
2018-09-26 7:55 ` Michal Hocko
2018-09-26 18:25 ` Alexander Duyck
2018-09-26 18:52 ` Dan Williams
2018-09-27 11:20 ` Michal Hocko
2018-09-27 11:09 ` Michal Hocko
2018-09-27 12:25 ` Oscar Salvador
2018-09-27 13:13 ` Michal Hocko
2018-09-27 14:50 ` Oscar Salvador
2018-09-27 15:41 ` David Hildenbrand
2018-09-28 8:12 ` Oscar Salvador [this message]
2018-09-28 8:44 ` Oscar Salvador
2018-09-28 15:50 ` Dan Williams
2018-09-27 12:32 ` Oscar Salvador
2018-10-08 21:01 ` Dan Williams
2018-10-08 21:38 ` Alexander Duyck
2018-10-08 22:00 ` Dan Williams
2018-10-08 22:07 ` Alexander Duyck
2018-10-08 22:36 ` Alexander Duyck
2018-10-08 22:59 ` Dan Williams
2018-10-08 23:34 ` [mm PATCH] memremap: Fix reference count for pgmap in devm_memremap_pages Alexander Duyck
2018-10-09 0:20 ` Dan Williams
2018-10-09 17:00 ` [PATCH v5 4/4] mm: Defer ZONE_DEVICE page initialization to the point where we init pgmap Yi Zhang
2018-10-09 18:04 ` Dan Williams
2018-10-09 20:26 ` Alexander Duyck
2018-10-09 21:19 ` Dan Williams
2018-10-10 12:52 ` Yi Zhang
2018-10-10 15:27 ` Alexander Duyck
2018-10-11 8:17 ` Yi Zhang
2018-10-10 9:58 ` Michal Hocko
2018-10-10 16:39 ` Alexander Duyck
2018-10-10 17:24 ` Michal Hocko
2018-10-10 17:39 ` Alexander Duyck
2018-10-10 17:53 ` Michal Hocko
2018-10-10 18:13 ` Alexander Duyck
2018-10-10 18:52 ` Michal Hocko
2018-10-11 8:55 ` Michal Hocko
2018-10-11 17:38 ` Alexander Duyck
2018-10-11 18:22 ` Dan Williams
2018-10-17 7:52 ` Michal Hocko
2018-10-17 15:02 ` Alexander Duyck
2018-10-29 14:12 ` Michal Hocko
2018-10-29 15:59 ` Alexander Duyck
2018-10-29 16:35 ` Michal Hocko
2018-10-29 17:01 ` Alexander Duyck
2018-10-29 17:24 ` Michal Hocko
2018-10-29 17:34 ` Dan Williams
2018-10-29 17:45 ` Michal Hocko
2018-10-29 17:42 ` Alexander Duyck
2018-10-29 18:18 ` Michal Hocko
2018-10-29 19:59 ` Alexander Duyck
2018-10-30 6:29 ` Michal Hocko
2018-10-30 6:55 ` Dan Williams
2018-10-30 8:17 ` Michal Hocko
2018-10-30 15:57 ` Dan Williams
2018-10-30 8:05 ` Oscar Salvador
2018-10-29 15:49 ` Dan Williams
2018-10-29 15:56 ` Michal Hocko
2018-10-10 18:18 ` Dan Williams
2018-10-11 8:39 ` Yi Zhang
2018-10-11 15:38 ` Alexander Duyck
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