RE: [Patch v2 04/15] CIFS: Add support for direct pages in wdata

[Long Li <longli@microsoft.com>]

> Subject: Re: [Patch v2 04/15] CIFS: Add support for direct pages in wdata
> 
> On 5/30/2018 3:47 PM, Long Li wrote:
> > From: Long Li <longli@microsoft.com>
> >
> > Add a function to allocate wdata without allocating pages for data
> > transfer. This gives the caller an option to pass a number of pages
> > that point to the data buffer to write to.
> >
> > wdata is reponsible for free those pages after it's done.
> 
> Same comment as for the earlier patch. "Caller" is responsible for "freeing"
> those pages? Confusing, as worded.
> 
> >
> > Signed-off-by: Long Li <longli@microsoft.com>
> > ---
> >   fs/cifs/cifsglob.h  |  2 +-
> >   fs/cifs/cifsproto.h |  2 ++
> >   fs/cifs/cifssmb.c   | 17 ++++++++++++++---
> >   3 files changed, 17 insertions(+), 4 deletions(-)
> >
> > diff --git a/fs/cifs/cifsglob.h b/fs/cifs/cifsglob.h index
> > 56864a87..7f62c98 100644
> > --- a/fs/cifs/cifsglob.h
> > +++ b/fs/cifs/cifsglob.h
> > @@ -1205,7 +1205,7 @@ struct cifs_writedata {
> >   	unsigned int			tailsz;
> >   	unsigned int			credits;
> >   	unsigned int			nr_pages;
> > -	struct page			*pages[];
> > +	struct page			**pages;
> 
> Also same comment as for earlier patch, these are syntactically equivalent
> and maybe not needed to change.
> 
> >   };
> >
> >   /*
> > diff --git a/fs/cifs/cifsproto.h b/fs/cifs/cifsproto.h index
> > 1f27d8e..7933c5f 100644
> > --- a/fs/cifs/cifsproto.h
> > +++ b/fs/cifs/cifsproto.h
> > @@ -533,6 +533,8 @@ int cifs_async_writev(struct cifs_writedata *wdata,
> >   void cifs_writev_complete(struct work_struct *work);
> >   struct cifs_writedata *cifs_writedata_alloc(unsigned int nr_pages,
> >   						work_func_t complete);
> > +struct cifs_writedata *cifs_writedata_direct_alloc(struct page **pages,
> > +						work_func_t complete);
> >   void cifs_writedata_release(struct kref *refcount);
> >   int cifs_query_mf_symlink(unsigned int xid, struct cifs_tcon *tcon,
> >   			  struct cifs_sb_info *cifs_sb,
> > diff --git a/fs/cifs/cifssmb.c b/fs/cifs/cifssmb.c index
> > c8e4278..5aca336 100644
> > --- a/fs/cifs/cifssmb.c
> > +++ b/fs/cifs/cifssmb.c
> > @@ -1952,6 +1952,7 @@ cifs_writedata_release(struct kref *refcount)
> >   	if (wdata->cfile)
> >   		cifsFileInfo_put(wdata->cfile);
> >
> > +	kvfree(wdata->pages);
> >   	kfree(wdata);
> >   }
> >
> > @@ -2075,12 +2076,22 @@ cifs_writev_complete(struct work_struct
> *work)
> >   struct cifs_writedata *
> >   cifs_writedata_alloc(unsigned int nr_pages, work_func_t complete)
> >   {
> > +	struct page **pages =
> > +		kzalloc(sizeof(struct page *) * nr_pages, GFP_NOFS);
> 
> Why do you do a GFP_NOFS here but GFP_KERNEL in the earlier patch?

This is for the I/O write path. The earlier patch is for I/O read path. This code preserves the behavior from the buffer I/O code.

The write path is possibly used when memory is under pressure, so it's better not to call FS (and CIFS) that may result in a loop.

> 
> > +	if (pages)
> > +		return cifs_writedata_direct_alloc(pages, complete);
> > +
> > +	return NULL;
> > +}
> > +
> > +struct cifs_writedata *
> > +cifs_writedata_direct_alloc(struct page **pages, work_func_t
> > +complete) {
> >   	struct cifs_writedata *wdata;
> >
> > -	/* writedata + number of page pointers */
> > -	wdata = kzalloc(sizeof(*wdata) +
> > -			sizeof(struct page *) * nr_pages, GFP_NOFS);
> > +	wdata = kzalloc(sizeof(*wdata), GFP_NOFS);
> >   	if (wdata != NULL) {
> > +		wdata->pages = pages;
> >   		kref_init(&wdata->refcount);
> >   		INIT_LIST_HEAD(&wdata->list);
> >   		init_completion(&wdata->done);
> >
> --
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