linux-kernel - Re: [PATCH] PM / Hiberante : optimize swsusp

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Date:	Sat, 11 Apr 2015 02:20:16 +0200
From:	"Rafael J. Wysocki" <rjw@...ysocki.net>
To:	"Yeon, JeHyeon (Tom)" <Tom.Yeon@...driver.com>
Cc:	"pavel@....cz" <pavel@....cz>, "jroedel@...e.de" <jroedel@...e.de>,
	"BROWN, A LEONARD" <len.brown@...el.com>,
	"linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"Tom(JeHyeon) Yeon" <tomyeon750415lkml@...il.com>
Subject: Re: [PATCH] PM / Hiberante : optimize swsusp_free()

On Wednesday, March 25, 2015 01:49:36 AM Yeon, JeHyeon wrote:
> From 6cb5fffc41911a29212be52d4ce7e481f5077ccf Mon Sep 17 00:00:00 2001
> From: "Tom(JeHyeon) Yeon" <tom.yeon@...driver.com>
> Date: Thu, 19 Mar 2015 17:10:45 +0900
> Subject: [PATCH] PM / Hiberante : optimize swsusp_free()
> 
> Our team developed the snapshot booting.
> Fisrt of all, make a snapshot image, compress it and finally save it
> in the storage(like mmc).
> When the system is booting next time, bootloader read it from mmc,
> decompress it and jump to the kernel.
> In this circumstance, mili seconds is very important.
> So, I prepared this patch, but not applied because I missed the time
> to apply it.
> 
> And, I came across to find commit fdd64ed.
> It's very similar to the patch I prepared.

So the part of the changelog above this line is not really relevant.

But the below is OK.

> I think do { ... } while (fb_pfn != fr_pfn) operation is very similar
> to my patch. but, it takes a little more time to iterate.
> So suggest to iterate one of two maps and check whether the other map
> has the same pfn, finally free the page.
> 
> Signed-off-by: Tom(JeHyeon) Yeon <tom.yeon@...driver.com>

As for the patch itself ->

> ---
>  kernel/power/snapshot.c |   43 ++++++++++---------------------------------
>  1 file changed, 10 insertions(+), 33 deletions(-)
> 
> diff --git a/kernel/power/snapshot.c b/kernel/power/snapshot.c
> index c24d5a2..a1ad801 100644
> --- a/kernel/power/snapshot.c
> +++ b/kernel/power/snapshot.c
> @@ -726,14 +726,6 @@ static void memory_bm_clear_bit(struct memory_bitmap *bm, unsigned long pfn)
>  	clear_bit(bit, addr);
>  }
>  
> -static void memory_bm_clear_current(struct memory_bitmap *bm)
> -{
> -	int bit;
> -
> -	bit = max(bm->cur.node_bit - 1, 0);
> -	clear_bit(bit, bm->cur.node->data);
> -}
> -
>  static int memory_bm_test_bit(struct memory_bitmap *bm, unsigned long pfn)
>  {
>  	void *addr;
> @@ -1342,36 +1334,21 @@ static struct memory_bitmap copy_bm;
>  
>  void swsusp_free(void)
>  {
> -	unsigned long fb_pfn, fr_pfn;
> +	unsigned long pfn;
>  
>  	if (!forbidden_pages_map || !free_pages_map)
>  		goto out;
>  
>  	memory_bm_position_reset(forbidden_pages_map);
> -	memory_bm_position_reset(free_pages_map);
> -
> -loop:
> -	fr_pfn = memory_bm_next_pfn(free_pages_map);
> -	fb_pfn = memory_bm_next_pfn(forbidden_pages_map);
> -
> -	/*
> -	 * Find the next bit set in both bitmaps. This is guaranteed to
> -	 * terminate when fb_pfn == fr_pfn == BM_END_OF_MAP.
> -	 */
> -	do {
> -		if (fb_pfn < fr_pfn)
> -			fb_pfn = memory_bm_next_pfn(forbidden_pages_map);
> -		if (fr_pfn < fb_pfn)
> -			fr_pfn = memory_bm_next_pfn(free_pages_map);
> -	} while (fb_pfn != fr_pfn);
> -
> -	if (fr_pfn != BM_END_OF_MAP && pfn_valid(fr_pfn)) {
> -		struct page *page = pfn_to_page(fr_pfn);
> -
> -		memory_bm_clear_current(forbidden_pages_map);
> -		memory_bm_clear_current(free_pages_map);
> -		__free_page(page);
> -		goto loop;
> +	for ( ; ; ) {
> +		pfn  = memory_bm_next_pfn(forbidden_pages_map);
> +		if (BM_END_OF_MAP == pfn)

-> First, the usual way of writing such things is

		if (pfn == BM_END_OF_MAP)

(ie. the variable on the left-hand side of the operator).

Second, don't you need to do the pfn_valid() check here too?

> +			break;
> +		if (memory_bm_test_bit(free_pages_map, pfn)) {
> +			memory_bm_clear_bit(forbidden_pages_map, pfn);
> +			memory_bm_clear_bit(free_pages_map, pfn);
> +			__free_page(pfn_to_page(pfn));
> +		}
>  	}
>  
>  out:


-- 
I speak only for myself.
Rafael J. Wysocki, Intel Open Source Technology Center.
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