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Message-ID: <4547A6D7.5090309@comcast.net>
Date: Tue, 31 Oct 2006 14:41:11 -0500
From: John Richard Moser <nigelenki@...cast.net>
To: "Rafael J. Wysocki" <rjw@...k.pl>
CC: Alistair John Strachan <s0348365@....ed.ac.uk>,
Luca Tettamanti <kronos.it@...il.com>,
linux-kernel@...r.kernel.org
Subject: Re: Suspend to disk: do we HAVE to use swap?
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Rafael J. Wysocki wrote:
> On Tuesday, 31 October 2006 20:05, Alistair John Strachan wrote:
>> On Tuesday 31 October 2006 17:40, Luca Tettamanti wrote:
>>> Alistair John Strachan <s0348365@....ed.ac.uk> ha scritto:
>>>> On Tuesday 31 October 2006 06:16, Rafael J. Wysocki wrote:
>>>> [snip]
>>>>
>>>>> However, we already have code that allows us to use swap files for the
>>>>> suspend and turning a regular file into a swap file is as easy as
>>>>> running 'mkswap' and 'swapon' on it.
>>>> How is this feature enabled? I don't see it in 2.6.19-rc4.
>>> Swap files have been supported for ages. suspend-to-swapfile is very
>>> new, you need a -mm kernel and userspace suspend from CVS:
>>> http://suspend.sf.net
>> I know, I use swap files, and not a partition. This has prevented me from
>> using suspend to disk "for ages". ;-)
>>
>> Is userspace suspend REQUIRED for this feature?
>
> No, but unfortunately one piece is still missing: You'll need to figure out
> where your swap file's header is located.
>
> However, if you apply the attached patch the kernel will tell you where it is
> (after you do 'swapon' grep dmesg for 'swap' and use the value in the
> 'offset' field).
Nobody has answered this one yet: Once you 'swapon' doesn't the kernel
have (require?) the swap file opened writable? Simple mode:
IS THIS NOT EXTREMELY DANGEROUS?
>
> Please read Documentation/power/swsusp-and-swap-files.txt before you begin.
>
> Greetings,
> Rafael
>
>
>
>
> ------------------------------------------------------------------------
>
> ---
> mm/swapfile.c | 15 ++++++++++-----
> 1 file changed, 10 insertions(+), 5 deletions(-)
>
> Index: linux-2.6.18-rc6-mm2/mm/swapfile.c
> ===================================================================
> --- linux-2.6.18-rc6-mm2.orig/mm/swapfile.c
> +++ linux-2.6.18-rc6-mm2/mm/swapfile.c
> @@ -1047,7 +1047,8 @@ add_swap_extent(struct swap_info_struct
> * This is extremely effective. The average number of iterations in
> * map_swap_page() has been measured at about 0.3 per page. - akpm.
> */
> -static int setup_swap_extents(struct swap_info_struct *sis, sector_t *span)
> +static int setup_swap_extents(struct swap_info_struct *sis, sector_t *span,
> + sector_t *start)
> {
> struct inode *inode;
> unsigned blocks_per_page;
> @@ -1060,6 +1061,7 @@ static int setup_swap_extents(struct swa
> int nr_extents = 0;
> int ret;
>
> + *start = 0;
> inode = sis->swap_file->f_mapping->host;
> if (S_ISBLK(inode->i_mode)) {
> ret = add_swap_extent(sis, 0, sis->max, 0);
> @@ -1114,6 +1116,8 @@ static int setup_swap_extents(struct swa
> lowest_block = first_block;
> if (first_block > highest_block)
> highest_block = first_block;
> + } else {
> + *start = first_block;
> }
>
> /*
> @@ -1407,7 +1411,7 @@ asmlinkage long sys_swapon(const char __
> int swap_header_version;
> unsigned int nr_good_pages = 0;
> int nr_extents = 0;
> - sector_t span;
> + sector_t span, start;
> unsigned long maxpages = 1;
> int swapfilesize;
> unsigned short *swap_map;
> @@ -1608,7 +1612,7 @@ asmlinkage long sys_swapon(const char __
> p->swap_map[0] = SWAP_MAP_BAD;
> p->max = maxpages;
> p->pages = nr_good_pages;
> - nr_extents = setup_swap_extents(p, &span);
> + nr_extents = setup_swap_extents(p, &span, &start);
> if (nr_extents < 0) {
> error = nr_extents;
> goto bad_swap;
> @@ -1628,9 +1632,10 @@ asmlinkage long sys_swapon(const char __
> total_swap_pages += nr_good_pages;
>
> printk(KERN_INFO "Adding %uk swap on %s. "
> - "Priority:%d extents:%d across:%lluk\n",
> + "Priority:%d extents:%d across:%lluk offset:%llu\n",
> nr_good_pages<<(PAGE_SHIFT-10), name, p->prio,
> - nr_extents, (unsigned long long)span<<(PAGE_SHIFT-10));
> + nr_extents, (unsigned long long)span<<(PAGE_SHIFT-10),
> + (unsigned long long)start);
>
> /* insert swap space into swap_list: */
> prev = -1;
- --
We will enslave their women, eat their children and rape their
cattle!
-- Bosc, Evil alien overlord from the fifth dimension
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