From: Al Viro <viro@ZenIV.linux.org.uk>
To: Andy Lutomirski <luto@amacapital.net>
Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org,
Andrew Morton <akpm@linux-foundation.org>,
Ingo Molnar <mingo@kernel.org>,
Michel Lespinasse <walken@google.com>,
Hugh Dickins <hughd@google.com>, J??rn Engel <joern@logfs.org>
Subject: Re: [PATCH] mm: Downgrade mmap_sem before locking or populating on mmap
Date: Fri, 14 Dec 2012 07:27:55 +0000 [thread overview]
Message-ID: <20121214072755.GR4939@ZenIV.linux.org.uk> (raw)
In-Reply-To: <3b624af48f4ba4affd78466b73b6afe0e2f66549.1355463438.git.luto@amacapital.net>
On Thu, Dec 13, 2012 at 09:49:43PM -0800, Andy Lutomirski wrote:
> This is a serious cause of mmap_sem contention. MAP_POPULATE
> and MCL_FUTURE, in particular, are disastrous in multithreaded programs.
>
> Signed-off-by: Andy Lutomirski <luto@amacapital.net>
> ---
>
> Sensible people use anonymous mappings. I write kernel patches :)
>
> I'm not entirely thrilled by the aesthetics of this patch. The MAP_POPULATE case
> could also be improved by doing it without any lock at all. This is still a big
> improvement, though.
Wait a minute. get_user_pages() relies on ->mmap_sem being held. Unless
I'm seriously misreading your patch it removes that protection. And yes,
I'm aware of execve-related exception; it's in special circumstances -
bprm->mm is guaranteed to be not shared (and we need to rearchitect that
area anyway, but that's a separate story).
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WARNING: multiple messages have this Message-ID (diff)
From: Al Viro <viro@ZenIV.linux.org.uk>
To: Andy Lutomirski <luto@amacapital.net>
Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org,
Andrew Morton <akpm@linux-foundation.org>,
Ingo Molnar <mingo@kernel.org>,
Michel Lespinasse <walken@google.com>,
Hugh Dickins <hughd@google.com>, J??rn Engel <joern@logfs.org>
Subject: Re: [PATCH] mm: Downgrade mmap_sem before locking or populating on mmap
Date: Fri, 14 Dec 2012 07:27:55 +0000 [thread overview]
Message-ID: <20121214072755.GR4939@ZenIV.linux.org.uk> (raw)
In-Reply-To: <3b624af48f4ba4affd78466b73b6afe0e2f66549.1355463438.git.luto@amacapital.net>
On Thu, Dec 13, 2012 at 09:49:43PM -0800, Andy Lutomirski wrote:
> This is a serious cause of mmap_sem contention. MAP_POPULATE
> and MCL_FUTURE, in particular, are disastrous in multithreaded programs.
>
> Signed-off-by: Andy Lutomirski <luto@amacapital.net>
> ---
>
> Sensible people use anonymous mappings. I write kernel patches :)
>
> I'm not entirely thrilled by the aesthetics of this patch. The MAP_POPULATE case
> could also be improved by doing it without any lock at all. This is still a big
> improvement, though.
Wait a minute. get_user_pages() relies on ->mmap_sem being held. Unless
I'm seriously misreading your patch it removes that protection. And yes,
I'm aware of execve-related exception; it's in special circumstances -
bprm->mm is guaranteed to be not shared (and we need to rearchitect that
area anyway, but that's a separate story).
next prev parent reply other threads:[~2012-12-14 7:27 UTC|newest]
Thread overview: 44+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-12-14 5:49 [PATCH] mm: Downgrade mmap_sem before locking or populating on mmap Andy Lutomirski
2012-12-14 5:49 ` Andy Lutomirski
2012-12-14 7:27 ` Al Viro [this message]
2012-12-14 7:27 ` Al Viro
2012-12-14 11:14 ` Andy Lutomirski
2012-12-14 11:14 ` Andy Lutomirski
2012-12-14 14:49 ` Al Viro
2012-12-14 14:49 ` Al Viro
2012-12-14 16:12 ` Andy Lutomirski
2012-12-14 16:12 ` Andy Lutomirski
2012-12-16 8:41 ` Ingo Molnar
2012-12-16 8:41 ` Ingo Molnar
2012-12-16 17:04 ` Al Viro
2012-12-16 17:04 ` Al Viro
2012-12-16 17:48 ` Al Viro
2012-12-16 17:48 ` Al Viro
2012-12-16 18:49 ` Johannes Weiner
2012-12-16 18:49 ` Johannes Weiner
2012-12-16 19:53 ` Al Viro
2012-12-16 19:53 ` Al Viro
2012-12-16 20:16 ` Al Viro
2012-12-16 20:16 ` Al Viro
2012-12-15 2:17 ` [PATCH v2] " Andy Lutomirski
2012-12-15 2:17 ` Andy Lutomirski
2012-12-16 9:00 ` Ingo Molnar
2012-12-16 9:00 ` Ingo Molnar
2012-12-16 17:52 ` Andy Lutomirski
2012-12-16 17:52 ` Andy Lutomirski
2012-12-17 9:52 ` Ingo Molnar
2012-12-17 9:52 ` Ingo Molnar
2012-12-18 0:54 ` [PATCH v3] " Andy Lutomirski
2012-12-18 0:54 ` Andy Lutomirski
2012-12-20 2:22 ` Simon Jeons
2012-12-20 2:22 ` Simon Jeons
2012-12-16 12:39 ` [PATCH v2] " Michel Lespinasse
2012-12-16 12:39 ` Michel Lespinasse
2012-12-16 18:05 ` Andy Lutomirski
2012-12-16 18:05 ` Andy Lutomirski
2012-12-17 3:29 ` Michel Lespinasse
2012-12-17 3:29 ` Michel Lespinasse
2012-12-17 22:01 ` Andy Lutomirski
2012-12-17 22:01 ` Andy Lutomirski
2012-12-16 19:58 ` Linus Torvalds
2012-12-16 19:58 ` Linus Torvalds
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