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SubjectRe: [PATCH 03/10] mm: Add support for a filesystem to control swap files
On Fri, Sep 09, 2011 at 09:00:08AM -0400, Christoph Hellwig wrote:
> On Fri, Sep 09, 2011 at 12:00:47PM +0100, Mel Gorman wrote:
> > Currently swapfiles are managed entirely by the core VM by using
> > ->bmap to allocate space and write to the blocks directly. This
> > patch adds address_space_operations methods that allow a filesystem
> > to optionally control the swapfile.
> >
> > int swap_activate(struct file *);
> > int swap_deactivate(struct file *);
> > int swap_writepage(struct file *, struct page *, struct writeback_control *);
> > int swap_readpage(struct file *, struct page *);
>
> Just as the last two dozen times this came up:
>
> NAK
>
> The right fix is to add a filesystem method to support direct-I/O on
> arbitrary kernel pages, instead of letting the wap abstraction leak into
> the filesystem.

Ok.

I confess I haven't investigated this direction at
all yet. Is it correct that your previous objection was
http://linux.derkeiler.com/Mailing-Lists/Kernel/2009-10/msg00455.html
and the direct-IO patchset you were thinking of was
http://copilotco.com/mail-archives/linux-kernel.2009/msg87176.html ?

If so, are you suggesting that instead of swap_readpage and
swap_writepage I look into what is required for swap to use ->readpage
method and ->direct_IO aops?

--
Mel Gorman
SUSE Labs


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