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From: Dave Hansen <dave.hansen@intel.com>
To: Michal Hocko <mhocko@suse.com>, Wei Yang <richard.weiyang@gmail.com>
Cc: akpm@linux-foundation.org, linux-mm@kvack.org
Subject: Re: [PATCH] mm, sparse: drop pgdat_resize_lock in sparse_add/remove_one_section()
Date: Mon, 26 Nov 2018 23:17:40 -0800	[thread overview]
Message-ID: <3356e00d-9135-12ef-a53f-49d815b8fbfc@intel.com> (raw)
In-Reply-To: <20181127062514.GJ12455@dhcp22.suse.cz>

On 11/26/18 10:25 PM, Michal Hocko wrote:
> [Cc Dave who has added the lock into this path. Maybe he remembers why]

I don't remember specifically.  But, the pattern of:

	allocate
	lock
	set
	unlock

is _usually_ so we don't have two "sets" racing with each other.  In
this case, that would have been to ensure that two
sparse_init_one_section()'s didn't race and leak one of the two
allocated memmaps or worse.

I think mem_hotplug_lock protects this case these days, though.  I don't
think we had it in the early days and were just slumming it with the
pgdat locks.

I really don't like the idea of removing the lock by just saying it
doesn't protect anything without doing some homework first, though.  It
would actually be really nice to comment the entire call chain from the
mem_hotplug_lock acquisition to here.  There is precious little
commenting in there and it could use some love.

  reply	other threads:[~2018-11-27  7:17 UTC|newest]

Thread overview: 38+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-11-27  2:36 [PATCH] mm, sparse: drop pgdat_resize_lock in sparse_add/remove_one_section() Wei Yang
2018-11-27  6:25 ` Michal Hocko
2018-11-27  7:17   ` Dave Hansen [this message]
2018-11-27  7:30     ` Michal Hocko
2018-11-27  7:52     ` osalvador
2018-11-27  8:00       ` Michal Hocko
2018-11-27  8:18         ` osalvador
2018-11-28  0:29       ` Wei Yang
2018-11-28  8:19         ` Oscar Salvador
2018-11-28  8:41           ` Wei Yang
2018-11-28  1:01     ` Wei Yang
2018-11-28  8:47       ` Wei Yang
2018-11-28  9:17         ` Wei Yang
2018-11-28 12:34         ` Michal Hocko
2018-11-28  9:12 ` [PATCH v2] " Wei Yang
2018-11-28 10:28   ` David Hildenbrand
2018-11-29  8:54   ` Michal Hocko
2018-11-29  9:29     ` Wei Yang
2018-11-29 15:53   ` [PATCH v3 1/2] " Wei Yang
2018-11-29 15:53     ` [PATCH v3 2/2] mm, sparse: pass nid instead of pgdat to sparse_add_one_section() Wei Yang
2018-11-29 16:01       ` David Hildenbrand
2018-11-30  1:22         ` Wei Yang
2018-11-30  9:20           ` David Hildenbrand
2018-11-29 17:15       ` Michal Hocko
2018-11-29 23:57         ` Wei Yang
2018-11-29 16:06     ` [PATCH v3 1/2] mm, sparse: drop pgdat_resize_lock in sparse_add/remove_one_section() David Hildenbrand
2018-11-29 17:17       ` Michal Hocko
2018-11-30  4:28       ` Wei Yang
2018-11-30  9:19         ` David Hildenbrand
2018-11-30  9:52           ` Michal Hocko
2018-12-04  8:53             ` Wei Yang
2018-12-01  0:31           ` Wei Yang
2018-12-03 11:25         ` David Hildenbrand
2018-12-03 21:06           ` Wei Yang
2018-11-29 17:14     ` Michal Hocko
2018-12-04  8:56     ` [PATCH v4 " Wei Yang
2018-12-04  8:56       ` [PATCH v4 2/2] mm, sparse: pass nid instead of pgdat to sparse_add_one_section() Wei Yang
2018-12-04  9:24       ` [PATCH v4 1/2] mm, sparse: drop pgdat_resize_lock in sparse_add/remove_one_section() David Hildenbrand

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