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Message-ID: <20090912171930.GB29169@us.ibm.com>
Date: Sat, 12 Sep 2009 10:19:30 -0700
From: Sukadev Bhattiprolu <sukadev@...ux.vnet.ibm.com>
To: Peter Zijlstra <peterz@...radead.org>
Cc: Arnd Bergmann <arnd@...db.de>, linux-kernel@...r.kernel.org,
Oren Laadan <orenl@...columbia.edu>,
"Eric W. Biederman" <ebiederm@...ssion.com>,
Alexey Dobriyan <adobriyan@...il.com>,
Pavel Emelyanov <xemul@...nvz.org>,
Andrew Morton <akpm@...l.org>, torvalds@...ux-foundation.org,
mikew@...gle.com, mingo@...e.hu, hpa@...or.com,
Nathan Lynch <nathanl@...tin.ibm.com>, container@...ibm.com,
sukadev@...ibm.com
Subject: Re: [RFC][v6][PATCH 0/9] clone_with_pids() syscall
Peter Zijlstra [peterz@...radead.org] wrote:
| On Fri, 2009-09-11 at 09:47 -0700, Sukadev Bhattiprolu wrote:
| > | Also, if you're passing a struct, why not put nr_pids in there, and
| > | replace clone_pid_struct with a simple array? That would give us
| > |
| > | struct clone_struct {
| > | u64 flags;
| > | u64 child_stack;
| > | u32 child_tid;
| > | u32 parent_tid;
BTW, these two tids are __user pointers that kernel copies data into.
They should be u64 to avoid conversions in architecture specific code ?
| > | u32 nr_pids;
| > | u32 reserved1;
| > | u64 reserved2;
| > | };
| > |
| > | int clone2(struct clone_struct *cs, pid_t *pids);
| >
| > My only concern with this approach was the extra copy_from_user() in the
| > common case (i.e when not using the extended features). I assume the
| > overhead of copy_from_user() is small enough to be ignored ?
|
| I would think so, esp for small structure, it would be a cache hot copy.
| That is, for x86 I doubt it'll show up. No idea what hoops other arch
| have to jump through to get copy_from_user() doing what it does.
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