Date: Mon, 22 Oct 2007 21:16:17 +0100 (BST)
From: Hugh Dickins <hugh@veritas.com>
To: Pekka Enberg <penberg@cs.helsinki.fi>
cc: Erez Zadok <ezk@cs.sunysb.edu>, Ryan Finnie <ryan@finnie.org>,
       Andrew Morton <akpm@linux-foundation.org>, linux-kernel@vger.kernel.org,
       linux-fsdevel@vger.kernel.org, cjwatson@ubuntu.com, linux-mm@kvack.org
Subject: Re: msync(2) bug(?), returns AOP_WRITEPAGE_ACTIVATE to userland
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On Mon, 15 Oct 2007, Pekka Enberg wrote:
> 
> I wonder whether _not setting_ BDI_CAP_NO_WRITEBACK implies that
> ->writepage() will never return AOP_WRITEPAGE_ACTIVATE for
> !wbc->for_reclaim case which would explain why we haven't hit this bug
> before. Hugh, Andrew?

Only ramdisk and shmem have been returning AOP_WRITEPAGE_ACTIVATE.
Both of those set BDI_CAP_NO_WRITEBACK.  ramdisk never returned it
if !wbc->for_reclaim.  I contend that shmem shouldn't either: it's
a special code to get the LRU rotation right, not useful elsewhere.
Though Documentation/filesystems/vfs.txt does imply wider use.

I think this is where people use the phrase "go figure" ;)

Hugh
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