RE: [PATCH-v2 3/3] pnfsblock: call blk_plug functions for direct IO

[<tao.peng@xxxxxxx>]

> -----Original Message-----
> From: Myklebust, Trond [mailto:Trond.Myklebust@xxxxxxxxxx]
> Sent: Friday, June 01, 2012 5:22 AM
> To: Peng Tao
> Cc: linux-nfs@xxxxxxxxxxxxxxx; bharrosh@xxxxxxxxxxx; Peng, Tao
> Subject: Re: [PATCH-v2 3/3] pnfsblock: call blk_plug functions for direct IO
> 
> On Tue, 2012-05-29 at 12:38 +0800, Peng Tao wrote:
> > NFS DIO bypasses generic DIO code path. So we need to plug/unplug
> > on our own.
> >
> > Signed-off-by: Peng Tao <tao.peng@xxxxxxx>
> > ---
> >  fs/nfs/blocklayout/blocklayout.c |   47 +++++++++++++++++++++++++++++++++++++-
> >  1 files changed, 46 insertions(+), 1 deletions(-)
> >
> > diff --git a/fs/nfs/blocklayout/blocklayout.c b/fs/nfs/blocklayout/blocklayout.c
> > index bab432f..b48b08b 100644
> > --- a/fs/nfs/blocklayout/blocklayout.c
> > +++ b/fs/nfs/blocklayout/blocklayout.c
> > @@ -251,6 +251,7 @@ bl_read_pagelist(struct nfs_read_data *rdata)
> >
> >  	dprintk("%s enter nr_pages %u offset %lld count %u\n", __func__,
> >  	       rdata->pages.npages, f_offset, (unsigned int)rdata->args.count);
> > +	BUG_ON(header->dreq && header->layout_private == NULL);
> >
> >  	if (!bl_check_alignment(f_offset, rdata->args.count, PAGE_CACHE_MASK))
> >  		goto use_mds;
> > @@ -320,9 +321,17 @@ out:
> >  	bl_put_extent(cow_read);
> >  	bl_submit_bio(READ, bio);
> >  	put_parallel(par);
> > +	if (header->dreq && !header->moreio) {
> > +		blk_finish_plug((struct blk_plug *)header->layout_private);
> > +		kfree(header->layout_private);
> 
> Wait... Why can't this just go in the block-specific ->pg_doio()
> callback? Why does it need to go to your
> read_pagelist()/write_pagelist()?
> 
You are right. It can be moved to .pg_doio. The DIO alignment check should be moved there as well and then we can avoid allocating unnecessary nfs_read/write_data. It also eliminates the change in struct nfs_pgio_header.

Thanks,
Tao

> > +	}
> >  	return PNFS_ATTEMPTED;
> >
> > - use_mds:
> > +use_mds:
> > +	if (header->dreq) {
> > +		blk_finish_plug((struct blk_plug *)header->layout_private);
> > +		kfree(header->layout_private);
> > +	}
> >  	dprintk("Giving up and using normal NFS\n");
> >  	return PNFS_NOT_ATTEMPTED;
> >  }
> > @@ -575,6 +584,8 @@ bl_write_pagelist(struct nfs_write_data *wdata, int sync)
> >  	unsigned long blkmask = PAGE_CACHE_MASK;
> >
> >  	dprintk("%s enter, %Zu@%lld\n", __func__, count, offset);
> > +	BUG_ON(header->dreq && header->layout_private == NULL);
> > +
> >  	/* Check for alignment first */
> >  	if (header->dreq)
> >  		blkmask = NFS_SERVER(header->inode)->pnfs_blksize - 1;
> > @@ -740,8 +751,16 @@ out:
> >  	bl_put_extent(be);
> >  	bl_submit_bio(WRITE, bio);
> >  	put_parallel(par);
> > +	if (header->dreq && !header->moreio) {
> > +		blk_finish_plug((struct blk_plug *)header->layout_private);
> > +		kfree(header->layout_private);
> > +	}
> >  	return PNFS_ATTEMPTED;
> >  out_mds:
> > +	if (header->dreq) {
> > +		blk_finish_plug((struct blk_plug *)header->layout_private);
> > +		kfree(header->layout_private);
> > +	}
> >  	bl_put_extent(be);
> >  	kfree(par);
> >  	return PNFS_NOT_ATTEMPTED;
> > @@ -1017,15 +1036,30 @@ bl_clear_layoutdriver(struct nfs_server *server)
> >  static void
> >  bl_pg_init_read(struct nfs_pageio_descriptor *pgio, struct nfs_page *req)
> >  {
> > +	BUG_ON(pgio->pg_layout_private != NULL);
> > +
> >  	if (!bl_check_alignment(req->wb_offset, req->wb_bytes, PAGE_CACHE_MASK))
> >  		nfs_pageio_reset_read_mds(pgio);
> >  	else
> >  		pnfs_generic_pg_init_read(pgio, req);
> > +
> > +	if (pgio->pg_dreq && pgio->pg_lseg) {
> > +		struct blk_plug *plug;
> > +		/* Freed in bl_read_pagelist */
> > +		plug = kmalloc(sizeof(struct blk_plug), GFP_KERNEL);
> > +		if (plug != NULL) {
> > +			blk_start_plug(plug);
> > +			pgio->pg_layout_private = plug;
> > +		} else
> > +			nfs_pageio_reset_read_mds(pgio);
> > +	}
> >  }
> >
> >  static void
> >  bl_pg_init_write(struct nfs_pageio_descriptor *pgio, struct nfs_page *req)
> >  {
> > +	BUG_ON(pgio->pg_layout_private != NULL);
> > +
> >  	if (pgio->pg_dreq) {
> >  		/* Direct write should be blksize aligned */
> >  		unsigned blkmask = NFS_SERVER(pgio->pg_inode)->pnfs_blksize - 1;
> > @@ -1038,6 +1072,17 @@ bl_pg_init_write(struct nfs_pageio_descriptor *pgio, struct nfs_page *req)
> >  		nfs_pageio_reset_write_mds(pgio);
> >  	else
> >  		pnfs_generic_pg_init_write(pgio, req);
> > +
> > +	if (pgio->pg_dreq && pgio->pg_lseg) {
> > +		struct blk_plug *plug;
> > +		/* Freed in bl_write_pagelist */
> > +		plug = kmalloc(sizeof(struct blk_plug), GFP_NOFS);
> > +		if (plug != NULL) {
> > +			blk_start_plug(plug);
> > +			pgio->pg_layout_private = plug;
> > +		} else
> > +			nfs_pageio_reset_write_mds(pgio);
> > +	}
> >  }
> >
> >  static const struct nfs_pageio_ops bl_pg_read_ops = {
> 
> --
> Trond Myklebust
> Linux NFS client maintainer
> 
> NetApp
> Trond.Myklebust@xxxxxxxxxx
> www.netapp.com

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