linux-kernel - Re: [PATCH 1/3] Add flag to identify block swap devices

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Message-ID: <AANLkTilt8st_RJryMPJ7aqqi5T04xOjBH8_mZbanSprs@mail.gmail.com>
Date:	Mon, 17 May 2010 12:35:20 -0700
From:	Hugh Dickins <hughd@...gle.com>
To:	Minchan Kim <minchan.kim@...il.com>
Cc:	Nitin Gupta <ngupta@...are.org>, Greg KH <greg@...ah.com>,
	Pekka Enberg <penberg@...helsinki.fi>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Nigel Cunningham <nigel@...onice.net>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Cyp <cyp561@...il.com>, driverdev <devel@...verdev.osuosl.org>,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/3] Add flag to identify block swap devices

On Mon, May 17, 2010 at 4:50 AM, Minchan Kim <minchan.kim@...il.com> wrote:
> On Mon, May 17, 2010 at 2:32 PM, Nitin Gupta <ngupta@...are.org> wrote:
>> Added SWP_BLKDEV flag to distinguish block and regular file backed
>> swap devices. We could also check if a swap is entire block device,
>> rather than a file, by:
>> S_ISBLK(swap_info_struct->swap_file->f_mapping->host->i_mode)
>> but, I think, simply checking this flag is more convenient.
>>
>> Signed-off-by: Nitin Gupta <ngupta@...are.org>
> Reviewed-by: Minchan Kim <minchan.kim@...il.com>
>
> We can enhance swap_show by the flag as further patch.

You mean, make swap_show() decide partition or file by SWP_BLKDEV
instead of its own test?

Actually, I'd prefer we don't embed SWP_BLKDEV further, because it's
a bit of a hack and not really necessary.  What ought to happen (though
perhaps it's silly to be expending code over an imaginary case) is a
map_swap_entry() call to convert the swap offset to physical page
within partition - no-op in the partition case, but correcting the file case.

But I wouldn't want to write that patch without testing it,
which I won't be doing for a while.

Hugh
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