Messages in this thread | | | Subject | Re: [PATCH] nfs: fix nfs_writepage() | From | Trond Myklebust <> | Date | Wed, 17 Oct 2007 14:49:26 -0400 |
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On Wed, 2007-10-17 at 19:36 +0200, Peter Zijlstra wrote: > On Wed, 2007-10-17 at 18:26 +0200, Peter Zijlstra wrote: > > On Wed, 2007-10-17 at 12:24 -0400, Trond Myklebust wrote: > > > On Wed, 2007-10-17 at 17:57 +0200, Peter Zijlstra wrote: > > > > On Wed, 2007-10-17 at 11:47 -0400, Trond Myklebust wrote: > > > > > On Wed, 2007-10-17 at 11:45 -0400, Trond Myklebust wrote: > > > > > > On Wed, 2007-10-17 at 17:30 +0200, Peter Zijlstra wrote: > > > > > > > > > > > > > The thing is, swapper_space just calls ->writepage() and expects the > > > > > > > page to be written out. So either the a_ops usage of swapper_space is > > > > > > > deviant or NFS' is. > > > > > > > > > > > > Could somebody please document WTF writepage() is supposed to do, and > > > > > > WTF page_mkwrite() is for? > > > > > > > > > > > > I thought that page_mkwrite() was supposed to finally allow us to deal > > > > > > with dirty pages in a clean manner: the caller gets to tell the > > > > > > filesystem that it wants the entire page written out, and then dirties > > > > > > the page. What is the point if the VM then expects to be able to > > > > > > circumvent this? > > > > > > > > > > Put differently: > > > > > * _who_ is dirtying the page when the swapper is trying to write > > > > > the page out? > > > > > * why are they not calling either page_mkwrite() or > > > > > commit_write()? > > > > > > > > I'm writing anonymous pages (I'm the crazy person doing swap over NFS). > > > > And anonymous is dirty by default. > > > > > > I'd really prefer to _know_ that these writes are coming from the > > > swapper. That makes it possible to give them a correct credential and > > > open context. > > > > > > Could you perhaps funnel them through a new a_op->swap_out() and default > > > back to ->writepage() for those filesystems that don't define it? > > > > Sure, will do that. > > OTOH these pages will have PageSwapCache() and IS_SWAPFILE(inode) will > be true, so ->writepage() can already know. Do you still prefer > ->swap_out() ?
I think it is cleaner. PageSwapCache() is currently internal to the mm layer, and doesn't need to be exported here. Then there is the issue of overloading ->writepage(), which I don't like at all: it muddies the semantics.
As for IS_SWAPFILE(), it would be nice to get rid of that one day...
Cheers Trond
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