linux-kernel - Re: [PATCH v4 3/3] fs, xfs: introduce MAP_DIRECT for creating block-map-sealed file ranges

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Date:   Tue, 15 Aug 2017 14:42:50 +0200
From:   Jan Kara <jack@...e.cz>
To:     Dan Williams <dan.j.williams@...el.com>
Cc:     darrick.wong@...cle.com, Jan Kara <jack@...e.cz>,
        linux-nvdimm@...ts.01.org, linux-api@...r.kernel.org,
        Dave Chinner <david@...morbit.com>,
        linux-kernel@...r.kernel.org, linux-xfs@...r.kernel.org,
        linux-mm@...ck.org, Jeff Moyer <jmoyer@...hat.com>,
        Alexander Viro <viro@...iv.linux.org.uk>, luto@...nel.org,
        linux-fsdevel@...r.kernel.org,
        Ross Zwisler <ross.zwisler@...ux.intel.com>,
        Christoph Hellwig <hch@....de>
Subject: Re: [PATCH v4 3/3] fs, xfs: introduce MAP_DIRECT for creating
 block-map-sealed file ranges

On Mon 14-08-17 23:12:22, Dan Williams wrote:
> diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
> index ff151814a02d..73fdc0ada9ee 100644
> --- a/include/linux/mm_types.h
> +++ b/include/linux/mm_types.h
> @@ -306,6 +306,7 @@ struct vm_area_struct {
>  	struct mm_struct *vm_mm;	/* The address space we belong to. */
>  	pgprot_t vm_page_prot;		/* Access permissions of this VMA. */
>  	unsigned long vm_flags;		/* Flags, see mm.h. */
> +	unsigned long fs_flags;		/* fs flags, see MAP_DIRECT etc */
>  
>  	/*
>  	 * For areas with an address space and backing store,

Ah, OK, here are VMA flags I was missing in the previous patch :) But why
did you create separate fs_flags field for this? on 64-bit archs there's
still space in vm_flags and frankly I don't see why we should separate
MAP_DIRECT or MAP_SYNC from other flags? After all a difference in these
flags must also prevent VMA merging (which you forgot to handle I think)
and they need to be copied on split (which happens by chance even now).

								Honza
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR