From: Hugh Dickins <hugh@veritas.com>
To: Nikita Danilov <Nikita@Namesys.COM>
Cc: Nick Piggin <piggin@cyberone.com.au>,
Andrew Morton <akpm@osdl.org>,
linux-mm@kvack.org
Subject: Re: [PATCH 0/5] mm improvements
Date: Wed, 4 Feb 2004 13:53:01 +0000 (GMT) [thread overview]
Message-ID: <Pine.LNX.4.44.0402041337350.3479-100000@localhost.localdomain> (raw)
In-Reply-To: <16416.62172.489558.39126@laputa.namesys.com>
On Wed, 4 Feb 2004, Nikita Danilov wrote:
>
> 4. I found that shmem_writepage() has BUG_ON(page_mapped(page))
> check. Its removal had no effect, and I am not sure why the check was
> there at all.
Sorry, that BUG_ON is there for very good reason. It's no disgrace
that your testing didn't notice the effect of passing a mapped page
down to shmem_writepage, but it is a serious breakage of tmpfs.
I'd have to sit here thinking awhile to remember if there are further
reasons why it's a no-no. But the reason that springs to mind is it
breaks the semantics of a tmpfs file mapped shared into different mms.
shmem_writepage changes the tmpfs-file identity of the page to swap
identity: so if it's unmapped later, the instances would then become
private (to be COWed) instead of shared.
If you go the writepage-while-mapped route (more general gotchas?
I forget), you'll have to make an exception for shmem_writepage.
Hugh
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next prev parent reply other threads:[~2004-02-04 13:53 UTC|newest]
Thread overview: 40+ messages / expand[flat|nested] mbox.gz Atom feed top
2004-02-04 9:39 Nick Piggin
2004-02-04 9:40 ` [PATCH 1/5] " Nick Piggin
2004-02-04 19:45 ` Rik van Riel
2004-02-09 7:00 ` Nick Piggin
2004-02-09 21:56 ` Rik van Riel
2004-02-04 9:40 ` [PATCH 2/5] " Nick Piggin
2004-02-04 10:10 ` Andrew Morton
2004-02-04 10:15 ` Nick Piggin
2004-02-04 15:27 ` Rik van Riel
2004-02-05 2:18 ` Nick Piggin
2004-02-04 9:41 ` [PATCH 3/5] " Nick Piggin
2004-02-04 15:28 ` Rik van Riel
2004-02-04 16:45 ` Nikita Danilov
2004-02-04 18:53 ` Andrew Morton
2004-02-05 2:10 ` Nick Piggin
2004-02-04 9:42 ` [PATCH 4/5] " Nick Piggin
2004-02-04 10:11 ` Andrew Morton
2004-02-04 10:19 ` Nick Piggin
2004-02-04 9:42 ` [PATCH 5/5] " Nick Piggin
2004-02-04 10:03 ` Nick Piggin
2004-02-04 10:18 ` Andrew Morton
2004-02-04 10:22 ` Nick Piggin
2004-02-04 13:25 ` [PATCH 0/5] " Nikita Danilov
2004-02-04 13:53 ` Hugh Dickins [this message]
2004-02-04 14:03 ` Nikita Danilov
2004-02-04 15:03 ` Hugh Dickins
2004-02-04 15:19 ` Nikita Danilov
2004-02-05 2:13 ` Nick Piggin
2004-02-05 14:03 ` Nikita Danilov
2004-02-05 15:11 ` Nick Piggin
2004-02-05 15:15 ` Nick Piggin
2004-02-05 15:20 ` Nikita Danilov
2004-02-05 15:33 ` Nick Piggin
2004-02-05 15:46 ` Nikita Danilov
2004-02-05 15:56 ` Nick Piggin
2004-02-05 16:03 ` Nikita Danilov
2004-02-05 16:09 ` Nick Piggin
2004-02-04 18:33 ` Andrew Morton
2004-02-04 20:54 ` Hugh Dickins
2004-02-04 21:04 ` Andrew Morton
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