Re: [RFC] pnfs: Add per-LD-info to nfs_pageio_descriptor

[Benny Halevy <bhalevy@tonian.com>]

On 2011-08-29 20:22, Boaz Harrosh wrote:
> 
> What do you guys think? would it be acceptable to add a per-layout
> private-data to nfs_pageio_descriptor?
> 
> In obj-LD we have bunch of constrains on the size of the IO that
> involves some 64bit divisions, and math. These calculations are only
> needed to be preformed once when the offset of the first page is
> known. Then a simple wb_bytes can cache the results for subsequent
> calls. (And cannot be calculated before we know the IO's offset)
> 
> Also I might want to allocate the io_state earlier at the insert
> of the first page instead of at the actual call to write/read_pagelist,
> again, for the same reason above.
> 
> Today we get by because at the very end, if some constraints hit
> and not the full IO was preformed then we only set r/wdata->res.count
> to less then what was requested and these pages that are outside of
> the IOed range get to be read/written as part of a future request. But
> this is sub-optimal because that is done only at read/write_done time.
> By then the contiguous pages were already submitted to requests and
> the few left-over pages get submitted as their own request. This causes
> a seeky, unaligned and additional small IOs which, if calculated for at
> coalesce time, would be spared. With the up coming raid5/6 code this
> can cost dearly. (A single simple large contiguous IO becomes bunch of
> read-modify-write IOs)
> 
> I can see that also at filelayout_pg_test there are two 64bit divisions
> preformed on every page insert which could be optimized to a simple
> compare.
> 
> [BTW: Perhaps change the .write/read_pagelist() API to directly receive
>  the nfs_pageio_descriptor and avoid all the duplication of types and
>  members copy
> ]
> 
> I'm making pg_ld_private as a "long" because a long is good for a pointer
> as well as an integer.

I really prefer it to be a void * rather than long for the same reason
just as used in practically every other place.

Benny

> 
> Signed-off-by: Boaz Harrosh <bharrosh@panasas.com>
> 
> ---
> diff --git a/include/linux/nfs_page.h b/include/linux/nfs_page.h
> index e2791a2..c86bae5 100644
> --- a/include/linux/nfs_page.h
> +++ b/include/linux/nfs_page.h
> @@ -77,6 +77,7 @@ struct nfs_pageio_descriptor {
>  	int			pg_error;
>  	const struct rpc_call_ops *pg_rpc_callops;
>  	struct pnfs_layout_segment *pg_lseg;
> +	long pg_ld_private;
>  };
>  
>  #define NFS_WBACK_BUSY(req)	(test_bit(PG_BUSY,&(req)->wb_flags))
> --
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