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