From: Andi Kleen <ak@suse.de>
To: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: linux-mm@kvack.org, akpm@linux-foundation.org, mel@skynet.ie,
eric.whitney@hp.com, clameter@sgi.com
Subject: Re: [PATCH/RFC 1/8] Mem Policy: Write lock mmap_sem while changing task mempolicy
Date: Thu, 6 Dec 2007 22:24:58 +0100 [thread overview]
Message-ID: <200712062224.58812.ak@suse.de> (raw)
In-Reply-To: <20071206212053.6279.27183.sendpatchset@localhost>
On Thursday 06 December 2007 22:20:53 Lee Schermerhorn wrote:
> PATCH/RFC 01/08 Mem Policy: Write lock mmap_sem while changing task mempolicy
>
> Against: 2.6.24-rc2-mm1
>
> A read of /proc/<pid>/numa_maps holds the target task's mmap_sem
> for read while examining each vma's mempolicy. A vma's mempolicy
> can fall back to the task's policy. However, the task could be
> changing it's task policy and free the one that the show_numa_maps()
> is examining.
But do_set_mempolicy doesn't actually modify the mempolicy. It just
replaces it using essentially Copy-on-write.
If the numa_maps holds a proper reference count (I haven't
checked if it does) it can keep the old unmodified one as long as it wants.
I don't think a write lock is needed.
-Andi
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next prev parent reply other threads:[~2007-12-06 21:24 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2007-12-06 21:20 [PATCH/RFC 0/8] Mem Policy: More Reference Counting/Fallback Fixes and Misc Cleanups Lee Schermerhorn
2007-12-06 21:20 ` [PATCH/RFC 1/8] Mem Policy: Write lock mmap_sem while changing task mempolicy Lee Schermerhorn
2007-12-06 21:24 ` Andi Kleen [this message]
2007-12-06 21:34 ` Lee Schermerhorn
2007-12-06 21:20 ` [PATCH/RFC 2/8] Mem Policy: Fixup Fallback for Default Shmem Policy Lee Schermerhorn
2007-12-06 21:21 ` [PATCH/RFC 3/8] Mem Policy: Mark shared policies for unref Lee Schermerhorn
2007-12-06 21:21 ` [PATCH/RFC 4/8] Mem Policy: Document {set|get}_policy() vm_ops APIs Lee Schermerhorn
2007-12-06 21:21 ` [PATCH/RFC 5/8] Mem Policy: Rework mempolicy Reference Counting [yet again] Lee Schermerhorn
2007-12-06 21:21 ` [PATCH/RFC 6/8] Mem Policy: Use MPOL_PREFERRED for system-wide default policy Lee Schermerhorn
2007-12-06 21:21 ` [PATCH/RFC 7/8] Mem Policy: MPOL_PREFERRED cleanups for "local allocation" Lee Schermerhorn
2007-12-06 21:21 ` [PATCH/RFC 8/8] Mem Policy: Fix up MPOL_BIND documentation Lee Schermerhorn
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