From: Andrew Morton <akpm@osdl.org>
To: Andrea Arcangeli <andrea@suse.de>
Cc: hugh@veritas.com, torvalds@osdl.org, linux-kernel@vger.kernel.org
Subject: Re: anon-vma (and now filebacked-mappings too) mprotect vma merging [Re: 2.6.5-rc2-aa vma merging]
Date: Sat, 3 Apr 2004 17:13:58 -0800 [thread overview]
Message-ID: <20040403171358.5dec3987.akpm@osdl.org> (raw)
In-Reply-To: <20040404010147.GS2307@dualathlon.random>
Andrea Arcangeli <andrea@suse.de> wrote:
>
> BTW, now that the lookup on the
> prio-tree is immediate the i_shared_sem has no reason anymore to be a
> semaphore either, it should go back to a spinlock like in 2.4, like the
> anon_vma is also protected by a spinlock.
That change was made for scheduling latency reasons, mainly due to huge
pagetable walks in zap_page_range():
i_shared_lock is held for a very long time during vmtruncate() and
causes high scheduling latencies when truncating a file which is
mmapped. I've seen 100 milliseconds.
So turn it into a semaphore. It nests inside mmap_sem. This
change is also needed by the shared pagetable patch, which needs to
unshare pte's on the vmtruncate path - lots of pagetable pages need to
be allocated and they are using __GFP_WAIT.
If we no longer hold that lock during pte takedown then sure, it would
be better if we had a spinlock in there.
next prev parent reply other threads:[~2004-04-04 1:14 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <Pine.LNX.4.44.0403291957240.19124-100000@localhost.localdomain>
2004-03-29 19:45 ` 2.6.5-rc2-aa vma merging Hugh Dickins
2004-04-02 11:34 ` Hugh Dickins
2004-04-02 15:35 ` Andrea Arcangeli
2004-04-03 1:26 ` anon-vma (and now filebacked-mappings too) mprotect vma merging [Re: 2.6.5-rc2-aa vma merging] Andrea Arcangeli
2004-04-03 17:06 ` Hugh Dickins
2004-04-03 17:24 ` Andrea Arcangeli
2004-04-03 18:46 ` Andrea Arcangeli
2004-04-03 19:29 ` Hugh Dickins
2004-04-04 1:01 ` Andrea Arcangeli
2004-04-04 1:13 ` Andrew Morton [this message]
2004-04-04 1:32 ` Andrea Arcangeli
2004-04-04 1:43 ` Andrew Morton
2004-04-04 1:55 ` Andrea Arcangeli
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