triggering do_writepages

triggering do_writepages

[Kapish K]

Hello,
  I have a ( possibly simple ) question on
how to trigger a do-writepages to get
called, for a particular filesystem, on
which I am issuing write calls. Any code
that I put into the generic_file_write code
( around prepare_write or commit_write )
gets triggered when a write is issues, but I
don't seem to be getting do_writepages
invoked for that filesystem ( when I check
the sb pointer for my particular filesystem ). 
Am I missing something basic in here?
Any pointers will be most helpful
Thanks in advance

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Re: triggering do_writepages

[girish]

Hi,
  writepage is used when ever there is pressure for memory from VM system
and for mmaped files. I guess  writepage need not be triggered explictly. If
you want to add a functionaly for a writepage you can stack it at writepage,
which will be called implicitly


----- Original Message -----
From: "Kapish K" <kapish@ureach.com>
To: <linux-fsdevel@vger.kernel.org>
Sent: Tuesday, November 19, 2002 12:29 PM
Subject: triggering do_writepages


>
> Hello,
>   I have a ( possibly simple ) question on
> how to trigger a do-writepages to get
> called, for a particular filesystem, on
> which I am issuing write calls. Any code
> that I put into the generic_file_write code
> ( around prepare_write or commit_write )
> gets triggered when a write is issues, but I
> don't seem to be getting do_writepages
> invoked for that filesystem ( when I check
> the sb pointer for my particular filesystem ).
> Am I missing something basic in here?
> Any pointers will be most helpful
> Thanks in advance
>
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Re: triggering do_writepages

[Bryan Henderson]

writepage also runs when the system synchronizes a file's cache in any of
numerous ways (fsync() system call, sync() system call, filesystem driver
calls f_datasync() kernel service, ...).

Re: triggering do_writepages

[Jan Hudec]

On Tue, Nov 19, 2002 at 01:59:33AM -0500, Kapish K wrote:
> 
> Hello,
>   I have a ( possibly simple ) question on
> how to trigger a do-writepages to get
> called, for a particular filesystem, on
> which I am issuing write calls. Any code
> that I put into the generic_file_write code
> ( around prepare_write or commit_write )
> gets triggered when a write is issues, but I
> don't seem to be getting do_writepages
> invoked for that filesystem ( when I check
> the sb pointer for my particular filesystem ). 
> Am I missing something basic in here?
> Any pointers will be most helpful
> Thanks in advance

... i can't find any do_writepages symbol...
Anyway, what is supposed to happen is, that in commit write you either
start the IO (and thus the write is done), or you mark the page dirty
(using set_page_dirty). Later, either when kernel needs to reuse the
page (during memory allocation), or when it decides the page is dirty
too long (in kflushd), it calls the writepage address_space method on
the page. This method must then start the IO (and setup a callback to
unlock it when IO completes and finish). If the IO completes OK, the
callback should set the page clean again so kernel can reuse it.

-------------------------------------------------------------------------------
						 Jan 'Bulb' Hudec <bulb@ucw.cz>